Periodic Table And Periodicity In The Properties Of Elements Topic A Periodic Table Synopsis:
WBBSE Class 10 Periodic Table Overview
Dobereiner’s Law of Triads: In 1817, German scientist Dobereiner first attempted to arrange the elements on the basis of their atomic weights. According to his Law of Triads, if three elements having similar properties are arranged in increasing order of their atomic weights, the atomic weight of the middie element in the triad is found to be the average of the atomic weights of the remaining two elements.
Newland’s Law of Octaves: When the known elements are arranged in increasing order of their atomic weights, the eighth element, starting from a given one, will show resemblance in physical and chemical properties with the first element. This is known as Newland’s Law of Octaves (1861).
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Mendeleev’s Periodic Law: In 1869, Mendeleev put forward the periodic law through which he established the relationship between atomic weight of an element to its physical and chemical properties.
The statement of the law was given as:
1. The physical and chemical properties of the elements are periodic functions of their atomic weights.
2. Almost at the same time, German scientist Lothar Meyer came to the same conclusion by observing that physical properties of the elements are changing periodically with their atomic weights.
Wbbse Class 10 Physical Science Solutions
Periodic Table: On the basis of his periodic law, Mendeleev constructed a table by arranging the elements in increasing order of their atomic weights. This table is known as Mendeleev’s periodic table.
Modem Periodic Law: In 1913, British scientist Moseley while observing the effects of X-rays on metals, concluded that atomic number is a more accurate and fundamental property of an element than its atomic weight. Accordingly, Mendeleev’s periodic law was modified. This modified form is known as the modern periodic law which states.
The physical and chemical properties of the elements are the periodic functions of their atomic number. In the periodic table, the horizontal rows of elements are called periods and the vertical columns of elements are called groups. The modified version of Mendeleev’s periodic table has 7 periods and 9 groups.
Wbbse Class 10 Periodic Table Of Elements
Long form of periodic table or Modern periodic table: The periodic table constructed on the basis of the electronic configuration of elements is known as long form of periodic table or the modern periodic table. It is also known as Bohr’s periodic table. It consists of 7 periods and 18 groups.
Elements of different groups are given some special names depending on their properties. For example:
| Group | Name | Example |
| Group 1 elements | Alkali metals | Li, Na. K, Rb |
| Group 2 elements | Alkaline earth metals | Be, Mg, Ca, Sr |
| Group 11 elements | Coinage metals | Cu, Ag, Au |
| Group 15 elements | Pnictogens | N, P, As, Sb |
| Group 16 elements | Chalcogens | 0, S, Se, Te |
| Group 17 elements | Halogens | F, Cl, Br, 1 |
| Group 18 elements | Noble gases | He, Ne, Ar, Kr |
The position of hydrogen in the periodic table is controversial. It shows certain properties that resemble the properties of both group-1 (alkali metals) as well as group- 17 elements (halogens). For these reasons, it can be placed in group 1 as well as in group- 17. Due to this peculiar nature of hydrogen, it is often called the rogue element’.
Periodic Table And Periodicity In The Properties Of Elements Topic A Periodic Table Short And Long Answer Type Questions:
Question 1. State Dobereiner’s law of Triads’? Why was the law discarded?
Answer:
Dobereiner’s law of Triads’:
If the elements of a triad i.e., a group of three elements having similar chemical properties, are arranged in increasing order of their atomic weights, then the atomic weight of the middle element is found to be equal or almost equal to the average of atomic weights of the other two elements.
Example: Li (7), Na (23) and K (39) have similar chemical properties and thus forms a triad. The average of atomic weights of Li and K = 7+39/2 = 23, which is the atomic weight of Na.
The law failed to arrange most of the elements known till then. It was only applicable for few elements. For these reasons, the law was discarded.
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Question 2. State Mendeleev’s periodic law. What was the basis of Mendeleev’s periodic law?
Answer:
Mendeleev’s periodic law:
1. The physical and chemical properties of the elements are periodic functions of their atomic weights.
2. Mendeleev examined the relationships between the atomic masses of the elements and their physical and chemical properties such as boiling point, melting point, density, atomic mass, the formula of hydrides and oxides of the elements etc. He observed that the physical and chemical properties of the elements change and periodically repeat with the change in atomic masses.
3. Based on these observations, he arranged the elements in the order of increasing atomic masses and formulated the periodic law.
Question 3. Evaluate the contribution of Lothar Meyer in the periodic classification of elements.
Answer:
The contribution of Lothar Meyer in the periodic classification of elements:
German scientist Lothar Meyer (1870) worked extensively on the relationship between physical properties of elements (such as atomic volume, melting point, boiling point etc.) and their atomic weights. He also stated a periodic law which was quite similar to what Mendeleev had proposed.
Wbbse Class 10 Physical Science Solutions
The work of both Mendeleev and Lothar Meyer are acknowledged towards periodic classification of elements. However, Mendeleev got greater recognition in this field as he put forward the theory much earlier than Lothar Meyer. However, the contribution of Lothar Meyer towards the concept of periodicity and periodic classification of elements cannot be neglected.
Wbbse Class 10 Periodic Table Of Elements
Question 4. What do you mean by period and group and groups were present in Mendeleev’s periodic table published in 1871?
Answer: The horizontal arrays of periodic table are termed as periods and the vertical arrays are termed as groups of the periodic table. There were 7 periods (1, 2, 3,…, 7) and 8 groups (1-8) in the periodic table published in 1871.
Question 5. How many elements were mentioned in the main version of Mendeleev’s periodic table published in 1871? Which element was absent in the table and why?
Answer:
1. 63 elements were mentioned in Mendeleev’s periodic table published in 1871.
2. Group ‘0’ (zero) was absent in Mendeleev’s periodic table (1871) as inert gases were not discovered at that time.
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Question 6. Why were subgroups needed in Mendeleev’s periodic tab?
Answer: In Mendeleev’s periodic table it was found that except for group ‘0’ (zero) and group 8, several elements of different properties are placed in the same group. Each of the groups except 0 and 8 is divided into two subgroups designated as ‘A’ and ‘B’. Properties of the elements of subgroups A and B are altogether different, except their valencies.
However, elements of the same subgroup exhibit more or less similar properties. E.g., the alkali metals of Group l-A are closely alike. But Group IA metals differ remarkably from the coinage metals of Group IB, although they have a common valency of 1.
Question 7. The atomic mass of argon (39.94) is greater than that of potassium (39.1), yet potassium was placed after Argon in Mendeleev’s periodic table—explain why.
Answer: Mendeleev’s main objective was to place elements with similar properties in the same class. That is why these two elements were placed in the group where their properties resemble with other elements although their atomic masses indicate just the reverse places in the periodic table.
Understanding Physical and Chemical Properties of Elements
Question 8. How was Mendeleev’s periodic table useful in the periodic classification of elements? Explain with an example.
Answer: The elements present in the same group of the periodic table show similarity in properties.
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1. So, if the property of one element in a specific group is known we can get an idea about the properties of the other elements present in the group.
2. If we know the properties of sodium of group- IA, the properties of other elements of that group namely potassium, rubidium and caesium can easily be evaluated.
Question 9. How was Mendeleev’s periodic table helpful in describing the structure and electronic configuration of different elements?
Answer: The elements present in the same subgroup of a group in Mendeleev’s periodic table have similar physical and chemical properties. Again, it is known that elements with similar properties have similar electronic configurations of their outermost orbits.
Thus, it can easily be correlated that elements of the same group have similar electronic configuration. Therefore, we can get an idea about the electronic configuration of other elements of a definite group, if the electronic configuration of any one element of the group is known. Similarly, from the knowledge of electronic configuration, we get an idea about the structure of atom.
Question 10. Discuss the limitations of Mendeleev’s periodic table.
Answer:
The limitations of Mendeleev’s periodic table:
Though Mendeleev was almost successful in arranging the elements on the basis of their properties in his periodic table, the periodic table had some serious drawbacks such as:
1. In some cases, in order to place the elements having similar properties in the same group, Mendeleev placed some elements with higher atomic weight before elements having lower atomic weight.
2. The position of hydrogen in Mendeleev’s periodic table was controversial.
3. In some cases, Mendeleev put elements having similar properties in different groups while elements having different properties in the same group.
4. Though the atomic weights of different isotopes are different, they were not given different positions in the periodic table.
Question 11. Mention the observation and inference of Moseley’s experiment on X-ray spectra.
Answer: In 1913, scientist Moseley made extensive research on the X-rays produced when cathode rays are bombarded on plates (target or anticathode) made of different metals.
Observation:
1. He observed that the X-rays produced due to collision of cathode rays with different metals have different frequencies. However, for a definite metal, the frequency of produced X-rays is constant.
2. He also observed when the square root of the frequencies of radiated X-rays was plotted against the atomic numbers of the elements (metals) used as anticathode, a straight line was obtained. However, no such straight line was obtained when atomic masses of the elements were plotted against the square root of the frequencies.
Inference: From the experiment, Moseley inferred that the properties of elements are a function of their atomic numbers and not their atomic masses.
Question 12. Write down the modified or modern periodic law. Mention the total number of periods and groups in the modern edition of Mendeleev’s periodic table.
Answer: The physical and chemical properties of the elements are a periodic function of their atomic numbers. There are 7 periods (1-7) and 9 groups (1, 8 and 0) in the modern edition of Mendeleev’s periodic table.
Question 13. Write down some differences between period and group in the periodic table.
Answer:
Differences between period and group in the periodic table are as follows:
| Period | Croup |
| 1. A period is a horizontal row of the periodic table. | 1. A group is a vertical column of the periodic table. |
| 2. There are 7 periods in the long form of the periodic table. | 2. There are 18 groups in the long form of the periodic table. |
| 3. The elements in a period differ in physical and chemical properties. | 3. The elements in each group have some similar properties but not entirely identical properties. |
| 4. Number of electronic shells remains the same for all elements in a period. | 4. Number of electronic shells increases gradually from top to bottom in a group. |
Periodic Trends in Chemical Properties
Question 14. The chemical properties of all the elements in the same period are not the same, but the chemical properties of the elements in the same group are similar— explain.
Answer: The chemical properties of the elements depend on the atomic number and hence on the electronic configuration of the atoms. Since the atomic number and electronic configuration of the elements in a particular period are different, their chemical properties are also different.
On the other hand, although the atomic numbers of different elements belonging to the same group are different, the electronic configurations of the outermost shell are similar. That is why their chemical properties are also similar to each other.
Question 15. Why are the elements arranged in increasing order of their atomic number in the long form of the periodic table, instead of their increasing atomic weight?
Answer: In 1913-14, British scientist Moseley, on the basis of his experiments on X-ray spectra of different atoms, explained that atomic number is a more fundamental property of an element than its atomic weight. It controls the physical and chemical properties of the elements. Again, after the discovery of isotopes, it was well-known that an element may contain atoms of different atomic weights. Thus, it was proved that atomic weight does not control the properties of an element. So, in the long form of the periodic table, elements are arranged in increasing order of their atomic number instead of atomic weight.
Question 16. Mention the differences between modern version of Mendeleev’s periodic table and the long form of the periodic table.
Answer:
The major differences between modern version of Mendeleev’s periodic table and long form of periodic table are:
| The modern version of Mendeleev’s periodic table | The long form of the periodic table |
| 1. In the modern version of Mendeleev’s periodic table, the elements are arranged on the basis of atomic number. | 1. In the long form of the periodic table, the elements are arranged on the basis of the electronic configuration of the atoms. |
| 2. In Mendeleev’s periodic table, there were 7 periods and 9 groups and each group from 1 to 7 was divided into A and B subgroups. | 2. In the long form of the periodic table, there are 7 periods and 18 groups and no group is divided into subgroups. |
Question 17. Which period is termed as the shortest period? Mention the groups where the elements of the shortest period reside.
Answer: The 1st period of the periodic table is termed as the shortest period. It contains only two elements. Among the two elements of the 1st period, Hydrogen belongs to group 1 and helium belongs to group 18 of the periodic table.
Question 18. What are the first and second short periods of the periodic table? Mention the total number of elements in each of these periods. What are the first and last elements in each of these periods and mention the corresponding groups to which they belong?
Answer: Second and third periods of the periodic table are termed as first and second short periods respectively. There are 8 elements in each of the short periods.
| Period | Name of the element | Group in which it is placed |
| First short period | Lithium (first element) Neon (last element) | Group 1 Group 18 |
| Second short period | Sodium (first element) Argon (last element) | Group 1 Group 18 |
Question 19. What is meant by ‘representative elements’?
Answer:
‘Representative elements’:
The elements of the 2nd and 3rd periods are abundant in nature. Apart from this, the elements of a certain group in these periods show much resemblance in properties in regular intervals. So, these elements are collectively called ‘typical or representative elements’.
[Apart from these elements, 8 elements from 4th period: K(19), Ca(20) and Ga(31) to Kr(36), 8 elements from 5th period: Rb(37), Sr(38) and ln(49) to Xe(54), 8 elements from 6th period: Cs(55), Ba(56) and Th(81) to Rn(86) and Two elements from 7th period: Fr(87) and Ra(88) are also known as representative elements.]
Question 20. What are alkali metals and alkaline earth metals? Why are they called so?
Answer:
Alkali metals
The elements present in group-IA or group-1 of the periodic table, i.e., lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs) and francium (Fr) are collectively called alkali metals. The oxides, hydroxides and carbonates of these metals are strongly alkaline in nature. So, they are called alkali metals.
Alkaline earth metals
The elements present in group-2A or group-2 of the periodic table, i.e., beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra) are collectively called alkaline earth metals.
Compounds of these elements are abundantly found in the earth’s crust and their oxides, hydroxides and carbonates are alkaline in nature. So, they are called alkaline earth metals.
Question 21. Write down the characteristics of alkali metals.
Answer:
Characteristics of alkali metals are:
1. Alkali metals are highly electropositive and they have a tendency to form cations by losing electrons from their valence shell.
2. Because of high reactivity these elements do not occur freely in nature.
3. Valence shell of alkali metals contains 1 electron and thus alkali metals are monovalent.
4. Oxides and hydroxides of alkali metals are strong bases and alkalies respectively.
5. Alkali metals form metallic hydroxides and hydrogen in reaction with water.
6. Alkali metals are good reducing agents. Ascending order of reducing the power of alkali metals is — Li < Na < K < Rb < Cs.
Question 22. Write down the alkaline earth metals.
Answer:
Characteristics of alkaline earth metals are:
1. Alkaline earth metals are highly electropositive and have a tendency to form cations by losing electrons from valence shell.
2. Because of high reactivity, these elements do not occur freely in nature. ‘
3. There are 2 electrons in the outermost shell of the alkaline earth metals and thus they are bivalent.
4. They are strong reducing agent. Ascending order of reducing power of alkaline earth metals is — Be < Mg < Ca < Sr < Ba .
5. Alkaline earth metals are present in, earth crust as oxides.
6. Alkaline earth metals form hydrogen and alkalies in reaction with water under suitable conditions.
& \mathrm{Ca}+2 \mathrm{H}_2 \mathrm{O} \frac{\text { room }}{\text { temperature }} \mathrm{Ca}(\mathrm{OH})_2+\mathrm{H}_2 \uparrow \\
& \mathrm{Mg}+2 \mathrm{H}_2 \mathrm{O} \longrightarrow \mathrm{Mg}(\mathrm{OH})_2+\mathrm{H}_2 \uparrow
\end{aligned}\)
Question 23. What are bridge elements? Why are they called so?
Answer:
Bridge elements:
1. The inert gases (He, Ne, Ar, Kr, Xe and Rn) present in group-0 or group-18 of the periodic table are known as bridge elements.
2. These elements act as a bridge between strong electronegative halogens of group-17 and strong electropositive alkali metals of group-1 of the next period. So, these elements are called bridge elements.
Question 24. What are transition elements?
Answer:
Transition elements:
The elements from scandium (Sc) to copper (Cu) in the fourth period, yttrium (Y) to silver in the 5th period, lanthanum (La) and hafnium (Hf) to gold (Au) in the 6th period are known as transition elements due to some specific characteristics in their electronic configurations.
Significance of Valence Electrons in Periodicity
Question 25. Write down some characteristics or properties of transition elements.
Answer:
Some characteristics or properties of transition elements
1. Except for mercury (Hg), all transition elements are solid metals.
2. Transition elements generally exhibit variable oxidation states and valencies.
3. They can form both ionic and covalent compounds.
4. Transition elements exhibit a very distinctive property of forming coloured coordination complexes.
5. A number of transition metals such as Cr, Mn, Fe, Co, Ni, Cu etc. and their compounds are used as catalysts.
6. Many transition metals form alloys.
Question 26. Which elements are known as pnictogens? Why are they named so?
Answer: The elements of group V.B. of Mendeleev’s periodic table or group 15 of the long form of the periodic table are known as pnictogens. E.g., nitrogen (N), phosphorous (P), arsenic (As), antimony (Sb), and bismuth (Bi).
The word pnictogen is derived from the Greek word pnicogens meaning ‘suffocating’ or ‘to choke’. The first member of group 15 is nitrogen which is a suffocating gas. That is why members of this group are known as pnictogens.
Question 27. What are chalcogens? Why are they called so?
Answer:
Chalcogens:
1. The elements of group 16 of the periodic table namely O, S, Se, Te and Po are collectively known as chalcogens.
2. The term ‘chalcogen’ means the producer of ores. Most of the metals are found as their oxide or sulphide ores in the earth’s crust. So, these elements are known as chalcogens.
Question 28. What are metalloids? Give example.
Answer:
Metalloids:
There are some elements which have certain characteristics common to both metals and nonmetals. These are called metalloids.
Examples of metalloids are arsenic(As ), antimony (Sb), and bismuth (Bi).
Question 29. What are trans-uranium elements? Mention two important characteristics of these elements?
Answer:
Trans-uranium elements
The elements placed after uranium (92U) in the 7th period of periodic table are known as transuranium elements.
1. All trans-uranium elements are radioactive.
2. All these elements are artificially synthesised.
Question 30. Isotopes of an element have not been given separate places in the periodic table— this is one of the major drawbacks of Mendeleev’s periodic table. Explain.
Answer: In Mendeleev’s periodic table, the elements were arranged in increasing order of their atomic weights. However, the isotopes of an element have different atomic weights. But, Mendeleev placed all the isotopes of an element in the same group and same period which violates the basic rule of periodic classification. So, it can be considered as a major drawback of Mendeleev’s periodic table.
But in modern periodic table, the elements are arranged in increasing order of their atomic numbers. As all the isotopes of an element have the same atomic number, they should be positioned in the same place in the periodic table according to modern periodic law. Hence, this is no longer a drawback in modern periodic table.
Question 31. Discuss three advantages of modern periodic table over Mendeleev’s periodic table.
Answer:
Three advantages of long form of periodic table over Mendeleev’s periodic table are discussed below:
1. In Mendeleev’s periodic table the elements were arranged in increasing order of their atomic weights and later in increasing order of their atomic numbers. But in long form of periodic table, the elements are arranged on the basis of their electronic configurations.
Elements having same electronic configuration in their outermost shell are placed in the same group. As the chemical properties are related to the electronic configuration of the outermost shell, the periodicity of properties of the elements are described more effectively in long form of the periodic table.
2. In Mendeleev’s periodic table, each group except group 8 and group 0, was divided into subgroups. But the elements of different subgroups of a definite group are not very similar in terms of their properties. In the modern periodic table, the concept of subgroups has been eliminated. Elements of different subgroups have been placed in completely different groups. Which is more scientific.
3. In Mendeleev’s periodic table, each period of group 8 had three elements, namely, (Fe, Co, Ni), (Ru, Rh, Pd) and (Os, Ir, Pt). This defied the basic rule of periodic classification. In the long form of periodic table, these elements are placed in different groups.
Question 32. Which elements are halogens? Why are these named so?
Answer:
1. Elements of Gr-17 in the modern periodic table i.e. F, Cl, Br, I, At etc. are termed as halogens.
2. The name ‘halogen’ means ‘salt-producing’. Several salts can be formed by the reaction of metal with these elements. Salts containing F, Cl or I have been found in seawater. That is why these elements are termed as halogens. Some salts of halogen are—NaCI (common salt), CaF2, NaBr, Kl etc.
Question 33. Write down the characteristics of halogen elements.
Answer:
Characteristics of halogen elements are:
1. Halogens are highly reactive and hence cannot be obtained in a free state in nature. Halogens forms halides with metals and nonmetals.
2. Among halogens, fluorine and chlorine are gaseous, bromine is liquid and iodine is solid. Astatine is the only radioactive halogen.
3. Halogens are highly electronegative (except Iodine). Descending order of electronegativity: F > Cl > Br > I.
4. Number of electrons in the valence shell of halogen elements is 7 and thushalogens are monovalent.
5. Halogens are non-metals and diatomic molecules.
6. Halogen elements are a strong oxidising agents. Descending order of oxidising power or halogens is— F > Cl > Br > I.
Question 34. Which elements form the noble gas family? Among noble gases which one is most chemically active?
Answer:
1. The Group zero of modified Mendeleev’s periodic table or Gr-18 of the long form of periodic table are designated as noble gases, e.g. He, Ne, Ar, Kr, Xe and Rn.
2. Among the noble gases (or inert gases) Xenon (Xe) is the most chemically reactive. State the differences in properties between alkali metals and halogens.
Question 35. State the differences in properties between alkali metals and halogens.
Answer:
The major differences in properties between alkali metals and halogens are as follows:
| Property | Alkali metals | Halogens |
| Physical state | Soft solid substances can be cut into pieces with a knife. | The diatomic molecule can be solid, liquid or gas. |
| Conductance | Good conductor of heat and electricity. | Do not conduct heat or electricity. |
| Ionisation energy | In a period, the alkali metal has the least ionisation energy. | In a period, the halogen has the| highest ionisation energy. |
| Electronegativity | The alkali metal is the least electronegative in a particular period. | The halogen is the most electronegative in a particular period. |
| Oxidising and reducing property | Strong reducing agents. | Strong oxidizing agents. |
| Property | Alkali metals | Halogens |
| Reaction with acids | React violently with acid to produce hydrogen. | Generally do not react with acids. |
| Formation of compounds | Form, ionic compounds with non-metals. | Form ionic compounds with metals and covalent compounds with non-metals. |
Question 36. Write down the differences between representative elements and transition elements.
Answer:
Differences between and transition elements representative elements are as follows:
| Representative elements | Transition elements |
| 1. The elements present in groups 12 and groups 13-17 are known as representative elements. | 1. The elements present in group 312 in the long form of the periodic table are known as transition elements. |
| 2. Most of the representative elements show single valency. | 2. Transition elements show multiple valencies. |
| 3. The compounds of representative elements are usually colourless. | 3. Most of the compounds formed by the transition elements are coloured. |
| 4. Representative elements consist of some metals, nonmetals and metalloids. | 4. All transition elements are metallic in nature. |
Question 37. Why is hydrogen called an element?
Answer:
While arranging the elements in increasing order of their atomic weights, Mendeleev observed that hydrogen shows similarity with both alkali metals of group-1A as well as with halogens of group-8B. So, hydrogen was placed in both group 1A and group 7B. Mendeleev faced difficulty in ascertaining a definite position for hydrogen and so he named it a ‘rogue element’.
Examples of Periodic Properties: Atomic Radius and Ionization Energy
Question 38. Write down Some similarities between hydrogen and alkali metals.
Answer:
Some similarities between hydrogen and alkali metals
1. Like the alkali metals of Gr-1, hydrogen shows mono-valency, high reactivity and electropositive character.
2. Both hydrogen and alkali metals are reducing in nature.
3. Both hydrogen and alkali metals have strong affinity for non-metals.
4. Hydrogen forms H2O with oxygen. Like hydrogen, alkali metals also form oxides e.g. Na20, K20 etc.
5. Like halogens, hydrogen reacts with halogens to form halide compounds.
Question 39. Write down some similarities in properties of hydrogen and halogen elements.
Answer:
Some similarities in properties of hydrogen and halogen elements:
1. Like halogens, hydrogen is diatomic, has high ionisation energy and non-metallic character.
2. Like hydrogen, halogens are mostly univalent.
3. Hydrogen combines with metals to form hydrides while halogens combine with metals to form halides.
4. Halogens may be obtained at the anode by electrolysis of molten metallic halides.
Question 40. Mention some limitations of long form of periodic table.
Answer:
Some limitations of long form of periodic table:
The long form of the periodic table successfully eliminated a number of drawbacks of Mendeleev’s periodic table. However, the long form to has a few limitations. Which are discussed below—
1. Even in long form of periodic table, the position of hydrogen is still controversial. Hydrogen cannot be placed in a definite group.
2. Depending on the electronic configuration, He should have been placed in group 2. But it is placed in group 18 with other noble gases.
3. Like Mendeleev’s periodic table, the lanthanides and actinides are placed separately in two different rows below the main periodic table. The elements could not be placed in individual groups in the periodic table.
Question 41. Mention the differences in the properties of alkali metals and hydrogen.
Answer:
The differences in properties of alkali metals and hydrogen are—
| Alkali metals | Hydrogen |
| 1. Most alkali metals are usually solid at room temperature. | 1. Hydrogen is gaseous at room temperature. |
| 2. Alkali metals are monoatomic. | 2. Hydrogen molecules are diatomic. |
| 3. Alkali metals are electropositive metals. | 3. Hydrogen is an electropositive non-metal. |
| 4. Alkali metals always form cations, e.g., Na⊕, and K⊕. | 4. Hydrogen can form both cation (H⊕), and anion (HΘ). |
| 5. Oxides of alkali metals are basic in nature. | 5. Oxide of hydrogen (H2O) is neutral in nature. |
Periodic Table And Periodicity In The Properties Of Elements Topic A Periodic Table Very Short Answer Type Questions Choose The Correct Answer:
Question 1. Which of the following sets of elements does not form a triad?
1. Ca, Sr, Ba
2. Li, Na, K
3. O, S, Se
4. Cl, Br, I
Answer: 3. O, S, Se
Question 2. The number of elements in the longest period and the incomplete period are respectively
1. 28,32
2. 32,28
3. 32,32
4. 18,28
Answer: 2. 32,28
Question 3. The elements that found no place in the original periodic table constructed by Mendeleev were
1. Transition metals
2. Alkali metals
3. Noble gases
4. Halogens
Answer: 3. Noble gases
Question 4. In Mendeleev’s periodic table, the arrangement of elements in the order of their increasing atomic weights was not maintained for which pair of elements?
1. C&N
2. S&Cl
3. K&Ar
4. K&Ca
Answer: 3. K&Ar
Question 5. The group having no subgroups in Mendeleev’s periodic table is
1. Group 2
2. Group 8
3. group 7
4. group 5
Answer: 2. Group 8
Question 6. Which group in Mendeleev’s period table contains more than one element in the same position?
1. Group 2
2. Group 3
3. Group 0
4. Group 8
Answer: 4. Group 8
Question 7. The number of elements in each position under group 8 is
1. 4
2. 5
3. 3
4. 2
Answer: 3. 3
Question 8. The pair of elements belonging to pnictogens is
1. N, P
2. P, O
3. F, Cl
4. Na, K
Answer: 1. N, P
Question 9. Moseley observed that the frequency (v) of X-rays produced when metal plates are bombarded with cathode rays is related to atomic number of elements (Z) as
1. v∝Z
2. √v∝ Z
3. v2∝Z
4. v = Z
Answer: 2. √v∝ Z
Question 10. The number of groups in the long form of the periodic table is
1. 9
2. 12
3. 13
4. 20
Answer: 3. 13
Question 11. In long form of periodic table, the elements are arranged on the basis of their
1. Atomic mass
2. Atomic number
3. Electronic configuration
4. Number of neutrons
Answer: 3. Electronic configuration
Question 12. In long form of periodic table, the alkali metals are placed in group
1. 1
2. 2
3. 3
4. 4
Answer: 1. 1
Question 13. In long form of periodic table, the alkaline earth metals are placed in group
1. 1
2. 2
3. 3
4. None of these
Answer: 2. 2
Question 14. In long form of periodic table, the halogens are placed in group
1. 15
2. 16
3. 17
4. 18
Answer: 3. 17
Question 15. In long form of periodic table, the coinage metals are placed in group
1. 11
2. 15
3. 17
4. 1
Answer: 1. 11
Question 16. In long form of periodic table, the chalcogens are placed in group
1. 16
2. 17
3. 13
4. 1
Answer: 4. 1
Question 17. Which of the following is a chalcogen?
1. Se
2. B
3. C
4. Ne
Answer: 1. Se
Question 18. In long form of periodic table, the noble gases are placed in group
1. 17
2. 18
3. 16
4. 15
Answer: 2. 18
Question 19. An example of a transition metal is
1. Ca
2. Mg
3. Fe
4. Al
Answer: 3. Fe
Question 20. In Mendeleev’s periodic table hydrogen can be placed
1. With halogens or with alkali metals
2. With chalcogens or with alkaline earth metals
3. With pnictogens or with coinage metals
4. With pnictogens or with alkaline earth metals
Answer: 1. With halogens or with alkali metals
Question 21. Which of the following is a coinage metal?
1. Iron
2. Silver
3. Aluminium
4. Nickel
Answer: 2. Silver
Question 22. A trans-uranium element is
1. Np
2. Ce
3. Lu
4. La
Answer: 1. Np
Question 23. The outermost shell of second period elements is
1. K-shell
2. L-shell
3. M-shell
4. N-shell
Answer: 2. L-shell
Question 24. Which of the following pair is not correct?
1. Coinage metal : Cu
2. Halogen: I
3. Alkaline earth metal: Fe
4. Inert element : Ne
Answer: 3. Alkaline earth metal: Fe
Question 25. Which one of the following is an alkali earth metal?
1. Rb
2. Ba
3. Sb
4. F
Answer: 2. Ba
Question 26. Total number of elements in the sixth period of modern long form of periodic table is
1. 2
2. 8
3. 18
4. 32
Answer: 4. 32
Question 27. Group 15 elements are called
1. Chalcogen
2. Pnictogan
3. Halogen
4. Aerogen
Answer: 2. Pnictogan
Question 28. To which group of the periodic table does 13X27 belong?
1. 14
2. 13
3. 15
4. 16
Answer: 2. 13
Question 29. Which of the following is not an alkali metal?
1. Rb
2. Cs
3. Ca
4. Na
Answer: 3. Ca
Question 30. Atomic number is more fundamental property of an element than atomic mass— the scientist who proved it is
1. Moseley
2. Lothar Meyer
3. Mendeleev
4. Dalton
Answer: 1. Moseley
Question 31. Which one is an alkali metal?
1. K
2. Mg
3. F
4. Ne
Answer: 1. K
Question 32. Which one of the following is not a transition element?
1. Fe
2. Co
3. Ca
4. Cr
Answer: 3. Ca
Question 33. Ca is
1. An alkali metal
2. An alkaline earth metal
3. Halogen
4. Inert element
Answer: 2. An alkaline earth metal
Question 34. Which one of the following is not a coinage metal?
1. Cu
2. Ag
3. Au
4. Fe
Answer: 4. Fe
Question 35. Number of rare earth elements is
1. 8
2. 12
3. 16
4. 14
Answer: 4. 14
Question 36. Which of the following elements represent the same period?
1. Li, Na, K
2. F, Cl, Al
3. Li, Mg, Ca
4. Cu, Ni, Zn
Answer: 4. Cu, Ni, Zn
Periodic Table And Periodicity In The Properties Of Elements Topic A Periodic Table Answer In Brief:
Question 1. The atomic weight of sodium is the average of the atomic weight of lithium and potassium. What can be inferred from this using the law of triads?
Answer: Using the law of triads, it can be inferred that the chemical properties of lithium, sodium and potassium are similar.
Question 2. Three elements A, B, and C obey Dobereiner’s law of triads. If the atomic weights of A and C are respectively 7 and 39, then find the atomic weight of B.
Answer: According to law of triads, the atomic weight of the middle element of the triad is the average of the atomic weights of the first and third elements.
Hence, atomic weight of B atomic weight of A + atomic weight of B = \(\frac{\text { atomic weight of } A+\text { atomic weight of } B}{2}\) =\(\frac{7+39}{2}\) = 23
Question 3. Newland’s law of octave is not applicable for which type of elements?
Answer: Newland’s law of octave is not applicable for heavy elements.
Question 4. On which basis did Mendeleev arrange the elements in the period table?
Answer: Mendeleev arranged the elements in the periodic table in increasing order of their atomic weights.
Question 5. How many groups in Mendeleev’s periodic table were divided into subgroups A & B?
Answer: In Mendeleev’s periodic table, seven (7) groups were divided into subgroups A & B.
Question 6. Which groups in Mendeleev’s periodic table (corrected version) do not contain any subgroup?
Answer: Zero (0) and Eighth (8) group.
Question 7. How many more elements are there in the second period than the first period of Mendeleev’s periodic table?
Answer: There are 6 more elements present in the 2nd period than the 1st period of Mendeleev’s periodic table.
Question 8. The initial form of Mendeleev’s periodic table does not contain noble gases. Why?
Answer: At the time when Mendeleev first published the periodic table, noble gases were not discovered yet. So, the noble gases did not find any place in the initial form of Mendeleev’s periodic table.
Question 9. What is the position of noble gases in modern version of Mendeleev’s periodic table?
Answer: In modern version of Mendeleev’s periodic table, the noble gases are placed in the ‘zero’ (0) group.
Question 10. The atomic masses of some elements were erroneous when Mendeleev constructed the periodic table. Why?
Answer: Valencies of the elements were incorrectly measured. These inaccurate valencies of elements were responsible for the erroneous values of atomic masses of some elements.
Question 11. Which element was predicted as eka-silicon by Mendeleev?
Answer: The element predicted by Mendeleev as eka-silicon is now known as germanium.
Question 12. Which element was predicted by Mendeleev as eka-aluminium?
Answer: Gallium was predicted by Mendeleev as eka-aluminium.
Question 13. What similarity is observed between Na and Cu regarding their positions in the periodic table?
Answer: Both Na and Cu were placed in group 1. Na was in group 1A and Cu was in group 1B.
Question 14. Which is the most electropositive nonradioactive alkali metal?
Answer: Caesium (Cs) is the most electropositive nonradioactive alkali metal.
Question 15. Which alkali metal is radioactive?
Answer: Francium (Fr) is a radioactive alkali metal.
Question 16. Name an alkali metal which is a liquid at 30°C.
Answer: Caesium is a liquid at 30°C
Question 17. Which alkaline earth metal is the heaviest?
Answer: Radium is the heaviest alkaline earth metal.
Question 18. Which alkaline earth metal is the lightest?
Answer: Beryllium is the lightest alkaline earth metal.
Applications of Periodic Table in Chemistry
Question 19. Which is the radioactive halogen?
Answer: The radioactive halogen is astatine (At).
Question 20. Which is the lightest halogen?
Answer: Fluorine is the lightest halogen.
Question 21. Name a halogen that shows reducing property.
Answer: Iodine shows reducing property.
Question 22. Which group in the periodic table contains elements in all the three states, namely solid, liquid and gas?
Answer: Group 17 (group-8B) of the periodic table contains elements in all the three states. Fluorine and chlorine are gases, bromine is liquid and iodine is solid at normal temperatures.
Question 23. Which property is similar in all transuranium elements?
Answer: All the trans-uranium elements are radioactive elements.
Question 24. Mention the period in which all the elements are radioactive.
Answer: The elements of the 7th period are all radioactive.
Question 25. Name a radioactive noble gas.
Answer: A radioactive noble gas is radon.
Question 26. What are pnictogens?
Answer: The elements of group 15 in the long form of periodic table are known as pnictogens.
Question 27. Name the noble gas present in 2nd period of the periodic table.
Answer: Neon (Ne) is the noble gas present in 2nd period of the periodic table.
Question 28. Mention the series to Which U belongs.
Answer: Uranium (U) belongs to actinide series.
Question 29. Which period of the periodic table is known as very short period? To which groups do the elements of this period belong?
Answer: The first period of the periodic table is known as very short period. The period consists of two elements— hydrogen and helium. Hydrogen is placed in group-1A (group-1 in the long form of the periodic table). Helium belongs to group 0 (group 18 in the long form of periodic table).
Question 30. What are inert gases? Which one of them is chemically most active?
Answer: The six elements, helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon belonging to group-0 (group-18) of the periodic table are known as inert gases. Xenon is the most reactive among all the inert gases.
Question 31. What are coinage metals?
Answer: Three metals namely, copper (Cu), silver (Ag) and gold (Au) were used to make coins in ancient times as well as in medieval period. So, these metals are also known as coinage metals.
Question 32. How many periods are termed as longest period and mention the periods?
Answer: Two periods of the long form of periodic table are termed as longest periods. They are 6th period and seventh period.
Question 33. How many elements are there in each of the longest periods of the periodic table?
Answer: 32 elements.
Question 34. Mention the position of isotopes of elements in the periodic table.
Answer: Isotopes reside in the same group with the corresponding elements.
Question 35. Which period contains all of the three types of element viz. metals, non-metals and metalloids?
Answer: Fourth period.
Question 36. Why do elements of a particular group resemble in properties? Or, Why do Na and K resemble in properties?
Answer: Due to the presence of a similar type of electron configuration in the valence shell, they show resemblance in properties.
Question 37. Name an alkali metal.
Answer: Example of an alkali metal is sodium (Na).
Question 38. Which gas is produced in reaction with water and alkali metals?
Answer: Hydrogen gas.
Question 39. In which group of the modern periodic table do the alkaline earth metals reside?
Answer: Group 2.
Question 40. Name the halogen element which belongs to the same period where sulphur resides.
Answer: Chlorine (Cl).
Question 41. Name the liquid non-metal.
Answer: Bromine (Br).
Question 42. Which halogen element forms rapidly in reaction with water?
Answer: Fluorine (F).
Question 43. Which group of the modern periodic table belongs to the inert gases?
Answer: Group 18.
Question 44. Name the inert gas of the first period of the periodic table.
Answer: Helium (He).
Question 45. Name the inert gas residing at the 2nd period of the long form of periodic table.
Answer: Neon (Ne).
Question 46. State whether the transition elements are metals or non-metals.
Answer: Transition elements are metals.
Question 47. Which transition element is a liquid metal?
Answer: Mercury (Hg).
Question 48. Give example of noble metal.
Answer: Platinum (Pt)
Question 49. Elements of which group of the periodic table is termed as chalcogens?
Answer: Group-16 elements are termed as chalcogens.
Question 50. Mention the group of the rare earth elements in the periodic table.
Answer: Rare earth elements are present in the 3rd group of the modern periodic table.
Question 51. Name the lanthanide element of lowest atomic number.
Answer: Cerium (Ce) of atomic number 58.
Question 52. Mention two elements of the periodic table which are formed in laboratory.
Answer: Neptunium (Np, Atomic no: 93) and nobelium (No, atomic no: 102)
Question 53. Hydrogen and alkali metals form similar type of oxides. Mention a difference between those oxides.
Answer: Oxide of hydrogen ( H2O) is a neutral oxide while oxides of alkali metals are basic oxides for e.g. Na2O, K2O etc.
Question 54. How many elements are there in shortest period of the periodic table?
Answer: 2
Periodic Table And Periodicity In The Properties Of Elements Topic A Periodic Table Fill In The Blanks:
Question 1. Cl,_____ and I are members of a triad.
Answer: Br
Question 2. Noble gases are placed at extreme _______ of the periodic table.
Answer: Right
Question 3. In the modern periodic table, the elements are arranged on the basis of their ______ instead of ______
Answer: Atomic Numbers, and Atomic weights
Question 4. Moseley from his X-ray experiment came to the conclusion that ______ is the fundamental property of elements.
Answer: Atomic number
Question 5. The _______ period of periodic table is an incomplete period.
Answer: 7th
Question 6. The elements in zero group are chemical ______
Answer: Inert
Question 7. Hydrogen shows similar properties with ________ as well as ______
Answer: Alkali metals, halogens
Question 8. Trans-uranium elements start from the element with atomic number ______
Answer: 93
Question 9. There is no _______in the long form of periodic table.
Answer: Subgroup
Question 10. The elements of A and B subgroups in a given group of Mendeleev’s periodic table show no similarity except in their _______
Answer: Valances
Question 11. The elements sodium, potassium etc., are called alkali metals because the _____ and _______ of these elements are strong bases.
Answer: Oxides, hydroxides
Question 12. Among the halogens, _________ is liquid at normal temperature.
Answer: Bromine
Question 13. The elements Mg, Ca etc., are called alkaline earth metals because these elements are found in the earth’s crust as _______ and their hydroxides are ________ in nature.
Answer: Oxides, Alkaline
Question 14. Apart from ______ all other transition elements are solid metals.
Answer: Mercury
Question 15. There was no mention of _________ in Mendeleev’s old periodic table.
Answer: Inert gases
Question 16. According to the modern form of Mendeleev’s periodic table, halogens belong to the _______ group.
Answer: 7B
Question 17. There are _______ groups in the long form of periodic table.
Answer: 18
Question 18. The number of elements in each of the 2nd and 3rd periods of the long form of periodic table is ________
Answer: 8
Question 19. __________ is a radioactive halogen.
Answer: Astatine
Question 20. Gold, platinum and silver are examples of ______ metal.
Answer: Noble
Periodic Table And Periodicity In The Properties Of Elements Topic A Periodic Table State Whether True Or False:
Question 1. Atomic weight of Na is the average of the atomic weights of Li and K.
Answer: True
Question 2. The law of octaves was found to be satisfactory in case of light elements.
Answer: True
Question 3. The physical and chemical properties of the elements are the periodic functions of their atomic weights.
Answer: False
Question 4. The elements after uranium are called transition elements.
Answer: False
Question 5. Except H, all other elements in group 1 are reactive metals.
Answer: True
Question 6. The initial form of Mendeleev’s periodic table does not contain noble gases.
Answer: True
Question 7. Beryllium is the lightest metal among the alkaline earth metals.
Answer: True
Question 8. All the group-17 elements in the periodic table exist in a gaseous state at normal temperature.
Answer: False
Question 9. Cu, Ag and Au are known as coinage petals.
Answer: True
Question 10. Zn is a transition element.
Answer: False
Question 11. Ne (neon) is the most electronegative element.
Answer: False
Question 12. Law of Triads was given by scientist Lothar Meyer.
Answer: False
Question 13. There was no subgroup in group 8 of Mendeleev’s periodic table.
Answer: True
Question 14. In group 6B of Mendeleev’s periodic table elements of all three states viz. solid, liquid, and gas is present.
Answer: False
Question 15. Halogens are members of Group zero (0) of the modern periodic table.
Answer: False
Question 16. Halogen means sea-salt producer.
Answer: True
Question 17. A number of transition elements in the 4th period is 10.
Answer: True
Periodic Table and Periodicity in the Properties of Elements Topic B Chemical Periodicity Of Elements Synopsis:
1. Periodic property: The physical and chemical properties which show regular change while moving across a period from left to right and on going down a group from top to bottom are called periodic properties. Atomic radii, ionisation energy, electronegativity, oxidising and reducing properties etc., are periodic properties.
2. The variation of some physical and chemical properties of elements in a periodic table are as follows:
| Property | Variation across a period | Variation down a group |
| Atomic radii | Decreases in moving from | Increases in moving from top to bottom |
| Ionisation energy | Increases in moving from left to right | Decreases in moving from top to bottom |
| Electronegativity | Increases in moving from left to right | Decreases in moving from top to bottom |
| Oxidizing power | Increases in moving from left to right | Decreases in moving from top to bottom |
| Reducing power | Decreases in moving from left to right | Increases in moving from top to bottom |
Periodic Table and Periodicity in the Properties of Elements Topic B Chemical Periodicity Of Elements Short And Long Answer Type Questions:
Question 1. What is meant by ‘periodic properties’?
Answer:
‘Periodic properties’:
With the increase in atomic number, physical and chemical properties of the elements belonging to different periods in the periodic table show a gradual change and as we move along a period, the change is systemic and periodic.
Similarly, the elements present in a group show the periodic variation of similar properties with the increase in atomic number down the group. The physical and chemical properties of elements which show regular and periodic change across a period and down a group are known as periodic properties. Atomic radius, ionisation energy, electronegativity, oxidising and reducing properties etc., are some of the common periodic properties.
Question 2. Define atomic radius.
Answer:
Atomic radius:
The distance from the centre of the nucleus to the outermost shell containing the electrons is called the atomic radius.
Since it is not possible to isolate a single atom for the measurement of its radius, atomic radius is expressed as covalent radius, metallic radius and van der Waal’s radius.
Question 3. Define covalent radius. If the inter-nuclear distance of the two atoms in a hydrogen molecule is 0.74A, then find its covalent radius.
Answer:
Covalent radius
1. When two similar atoms are connected to each other by a single bond, one-half of the distance between their nuclei is called the covalent radius.
2. If the internuclear distance of the two atoms in a hydrogen molecule is 0.74 A, the covalent radius of hydrogen will be = 0.74/2 A = 0.37 A.
Question 4. How does atomic radius of the elements change from left to right in a period? Give reason.
Answer:
1. While moving from left to right across a period in the periodic table, the atomic radii or sizes of the atoms progressively decrease.
2. The principal quantum shell remains unchanged In the same period. So, the differentiating electrons enter the same shell. But due to an increase in the number of protons the value of +ve charge of the nucleus is increased. So attractive force of the nucleus for electrons in the outermost shell also increases which in turn gradually decreases the atomic radii.
Question 5. How does the atomic radius change down a group In the periodic table? Give reason.
Answer:
1. On moving down in any group of the periodic table, the atomic sizes rather the atomic radii of the elements increase.
2. On moving down a group, a new electronic shell is added to each succeeding element, though the number of electrons in the outermost shell remains the same. This tends to increase the atomic size.
At the same time, increase in nuclear charge with an increase in atomic number tends to decrease the atomic size. But the effect of the addition of a new electronic shell is so large that it outweighs the contractive effect of the increased nuclear charge. Hence, there occurs a gradual increase in atomic radii on moving down a group in the periodic table.
Question 6. (1) Arrange In decreasing order of atomic size—O, C, F, Li.
(2) Arrange in increasing order of atomic size—Br, F, I, Cl. lYz+VA
Answer:
(1)Given elements are members of the 2nd period of the periodic table. We know, across a period, atomic radius decreases from left to right. As a result, atomic size also decreases in the same fashion. So, the decreasing order of atomic size is Li > C > O > F.
(2)Given elements belong to Gr-17 of the long form of periodic table. We know, down the group atomic radius as well as atomic size gradually increases. So, the increasing order of atomic size is F < Cl < Br < I.
Common Mistakes in Understanding Periodic Trends
Question 7. What is the first ionisation energy of an element? Arrange the following elements in the increasing order of their first ionisation energy B, C, N, O and F.
Answer:
First ionisation energy of an element
The minimum amount of energy required to remove the most loosely bound electron from the outermost shell of an isolated gaseous atom of an element in its ground state to form a mono-positive ion is called the first ionisation energy of the element.
The ionisation energy of the given elements increases as— B<C<0<N<F.
Question 8. How does ionisation energy of elements change along a period and down a group in the periodic table?
Answer:
Variation along a period: On moving along a period from left to right, the ionisation energy of the elements generally increases, though some elements show exceptions to this trend. In a given period, the alkali metals present at the extreme left have the least ionisation energy while the noble gases at the extreme right have the highest ionisation energy.
Variation down a group: The ionisation energy of elements gradually decreases on moving down a group in the periodic table.
Question 9. (1)On which factors does the ionisation energy of an element depend?
(2) Why ionisation potentials of inert elements and alkali metals are very high and very low respectively?
Answer:
1. Factors influencing ionisation energy are:
(1)Atomic size: Ionisation energy decreases as the atomic size increases and vice-versa.
(2)Magnitude of nuclear charge: Ionisation energy increases with an increase in nuclear charge and vice-versa.
(3)Effect of the electronic configuration of the outermost shell: Ionisation energy increases with an increase in the stability of the electronic configuration.
2. Very high values of ionisation energies of inert gases are due to their highly stable electronic configuration. To remove an electron from this highly stable outer shell, a higher amount of energy is required making their ionisation energy so high.
On the other hand, alkali metals contain only one electron in their valence shell. By the removal of this electron, they can attain the stable electronic configuration of nearest inert gas. This is why the removal of an electron from alkali metals require a lower amount of energy making their ionisation energies low.
Question 10. Will ionisation energies of isotopes of an element be equal to each other? Explain.
Answer: Although the number of neutrons in the isotopes of an element are different, the number of electrons are same. As a consequence, electronic configurations are also the same. That is why the ionisation energies of these isotopes become equal to each other.
Question 11. Define electronegativity. Name the most electronegative and the least electronegative elements.
Answer:
Electronegativity:
Scientist Pauling defined electronegativity of an element as the tendency of an atom of the element to attract the bonded pair of electrons towards itself when it is covalently bonded to another atom, the most electronegative element is fluorine (F) and the least electronegative element is caesium (Cs).
Question 12. How does the electronegativity of the elements change across a period on moving from left to right? Explain with reasons.
Answer: On moving from left to right across a period the nuclear charge of the elements increases and atomic size decreases. As a result, the nuclear force of attraction on the bonded electron pair increases.
Hence, on moving from left to right the electronegativity of elements gradually increases. The alkali metal of a particular period located at the extreme left of the period is the least electronegative while the halogen in group 17 located at the right is the most electronegative element.
Question 13. How does the electronegativity of elements change on moving down a group? Arrange the following elements in the increasing order of their electronegativity. F, Br, Cl, I.
Answer: On moving down a group, the atomic size of the elements increases. As a result, the nuclear force of attraction on the outermost electrons decreases even though the nuclear charge increases. Hence, on moving down a group electronegativity of the elements gradually decreases.
The increasing order of electronegativity of the given elements: I < Br < Cl < F
Question 14. (1) Arrange the following elements in order of electronegativity—P, Cl, Si, S.
(2)Order of electronegativity of halogens— K Br < Cl < F. Explain.
(3)Name the elements with the highest and lowest electronegativity.
Answer:
(1)Given elements belong to the 3rd period in the periodic table, we know across a period from left to right electronegativity gradually increases. Therefore the increasing order of electronegativity of the given elements- Si < P < S < Cl.
(2)Halogens belong to group 17 of the periodic table. Now down a- group, electronegativity gradually decreases from top to bottom. Therefore we have the increasing order of electronegativity as given—I < Br < Cl < P.
(3) Fluorine (F) is the most electronegative element and Caesium (Cs) is the least electronegative element.
Question 15. Discuss how the oxidising and reducing power of elements change across a period and down a group in the periodic table.
Answer:
Variation across a period: On moving from left to right across a period, the atomic number as well as a number of protons gradually increases by one unit. At the same time, number of electrons also increases in the same outermost subshell. So, on moving from left to right nuclear attractive force on the outermost electrons gradually increases and the tendency to lose the electrons decreases.
At the same time, the tendency to accept electrons increases. As a result, the elements at the left part of the periodic table show a greater tendency to release electrons while the elements at the right part of the periodic table show a greater tendency to accept electrons. Hence, on moving from left to right across a period, the reducing power of the elements decreases whereas oxidising power increases. Alkali metals in group-1 of each period are the strongest reducing agents while the halogens in group-17 of each period are the strongest oxidising agents.
Vauation down a group: On moving down a group, atomic size of the elements increases and hence attractive force between the nucleus and the outermost electrons decreases. So, on moving down a group, the tendency of the elements to lose electrons increases. Hence, on moving down a group, reducing power of elements increases whereas oxidising power decreases.
Question 16. Discuss the variation of oxidising and reducing properties of the elements across a period. Arrange the following elements as per the given direction
(1)Na, Al, Si, Mg, P, Cl, S (decreasing order of reducing power).
(2)I, Cl, F, Br (increasing order of oxidising power).
Answer: On moving from left to right across a period, the oxidising power of the elements gradually increases while the reducing power gradually decreases.
(1)Decreasing order of reducing the power of the given elements: Na > Mg>AI>Si > P > S > Cl
(2)Increasing order of oxidising power of the non-radioactive halogen is: I < Br < Cl < F
Question 17. Arrange the elements of group-1A and group-2A in the correct order with respect to the following properties—
(1)Atomic size,
(2)Ionisation energy or ionisation potential,
(3) Reducing power.
Answer: For group-1A elements,
(1)Increasing order of atomic size: H < Li < Na < K < Rb < Cs < Fr
(2)Decreasing order of ionisation energy: H > Li > Na > K > Rb > Cs > Fr
(3)Increasing order of reducing power: H < Li < Na < K < Rb < Cs < Fr
For group-2A element,
(1)Increasing order of atomic size: Be < Mg < Ca < Sr < Ba < Ra
(2)Decreasing order of ionisation energy: Be > Mg > Ca > Sr > Br > Ra
(3)Increasing order of reducing power: Be < Mg < Ca < Sr < Ba < Ra
Question 18. Arrange the halogens in the correct order with respect to the following properties
(1) Atomic size,
(2) Ionisation energy or ionisation potential,
(3) Oxidising power.
Answer: Increasing order of atomic size: F < Cl < Br < I < At
Decreasing order of ionisation energy: F > Cl > Br > I > At
Decreasing order of oxidising power: F > Cl > Br > I > At.
Question 19. Some elements of a definite -period are given in the order in which they appear in the periodic table-Li, Be, B, C, Q, F, Me
1. State the period to which the elements belong.
2. Which element of that period is absent here? Mention its position.
3. Which element among these shows III catenation?
4. Arrange F, Be and N in increasing order of electronegativity.
5. Which element among these is a halogen?
6. Which one is an alkaline earth metal?
Answer:
1. All these elements belong to 2nd period.
2. The element absent here is nitrogen. In the periodic table, it is present between C and 0.
3. C shows catenation property.
4. Increasing order of electronegativity— Be < N < F.
5. F is a halogen.
6. Be is an alkaline earth metal.
Question 20. The names of the elements of a group in the periodic table are as follows: (1) boron, (2) aluminium, (3) gallium, (4) indium, (5) thallium. Answer the following questions:
1. Which of these elements shows the maximum metallic character?
2. Which element has the highest electronegativity?
3. If the electronic configuration of aluminium is K.= 2, L = 8, M = 3, then how many valence electrons are there in thallium?
4. The atomic number of boron is 5. Write the formula of the compound formed when boron reacts with chlorine.
5. Which of these elements has the least ionisation energy?
6. How many valence electrons are there in the elements present at the right side of this group?
Answer: The answers are given below:
1. The maximum metallic character is shown by thallium.
2. Boron has the highest electronegativity.
3. Thallium also has 3 valence electrons.
4. The formula of the compound formed when boron reacts with chlorine is BCI3.
5. Thallium has the least ionisation energy.
6. There are 4 valence electrons in the elements present at the right side of this group.
Question 21. The atomic number of three elements &V>B and C are (Z-2), Zand (Z+l) respectively. B is an inert gas. 0 Which of these elements is the most electronegative?
1. Which element has the highest ionisation energy?
2. State the nature of the compound formed by A and C and write its formula.
Answer: The atomic number of B is Z and it is an inert gas. Therefore, it has 8 electrons in its outermost shell. Hence, element A (atomic number -I- 2) has (8 – 2) = 6 electrons in its valence shell and element C (atomic number = Z+1) has 1 electron in its valence shell, i.e., C is an alkali metal. Therefore, we can conclude that
1. A is the most electronegative element.
2. B is an inert gas. Hence, it possesses the highest ionisation energy.
3. The number of electrons in the valence shell of A is 6. Hence, its valency is 8-6 = 2. Similarly, the valency of C is 1 as it has one electron in its outermost shell
Therefore, the formula of the compound formed between A and C will be C2A. C is an alkali metal and A is an electronegative element. Hence, the nature of the compound formed by A and C will be electrovalent or ionic.
Question 22. The atomic number of the elements A, B and C are respectively 3,11 and 19.
1. State the position of these elements in Mendeleev’s periodic table as well as the long form of the periodic table.
2. Which one is the most reducing in nature?
3. State whether B will form a covalent or an ionic compound with chlorine.
Answer:
1. The position of the elements in the periodic table is given below:
| Element | Electronic configuration | Position in Mendeleev’s periodic table | Position in long form of the periodic table | |||||
| K | L | M | N | Period | Croup | Period | Group | |
| 3A | 2 | 1 | 2nd | IA | 2nd | 1 | ||
| 11B | 2 | 8 | 1 | 3rd | IA | 3rd | 1 | |
| 19C | 2 | 8 | 8 | 4th | IA | 4th | 1 | |
2. C is the strongest reducing agent.
3. The number of valence electrons in B is 1. Hence, it is an alkali metal. On the other hand, chlorine is a strongly electronegative element and a non-metal. So, B will form an ionic compound with chlorine.
Question 23. Mention the position of the following elements in the long form of the modern periodic table, 11Na, 9F,13AI
Answer:
| Element | Electronic configuration | Position in the long form of the periodic table | |||
| K | L | M | Period | Group | |
| 11Na | 2 | 8 | 1 | 3 | 1 |
| 13AI | 2 | 8 | 3 | 3 | 13 |
| 9F | 2 | 7 | 2 | 17 | |
Question 24. Assume the symbol of two elements are A and B and their atomic numbers are 7 and 20 respectively. Predict their positions in Mendeleev’s periodic table.
Answer:
| Element | Electronic configuration | Position in Mendeleev’s periodic table | ||||
| K | L | M | N | Period | Group | |
| A(7) | 2 | 5 | 2 | 5B | ||
| B(20) | 2 | 8 | 8 | 2 | 4 | 2A |
Question 25. Among Cl (17), Na (11), Mg (12), Ca (20), S (16) and F (9)
1. Which metallic elements belong to Group 2?
2. Which non-metallic elements belong to 3rd period of Mendeleev’s periodic table?
Answer:
| Element | Atomic No. | Electronic configuration | Position in the periodic table | Metal or nonmetal | ||||
| K | L | W | N | Period | Group | |||
| Cl | 17 | 2 | 8 | 7 | 3 | 7B | non-metal | |
| Na | 11 | 2 | 8 | 1 | 3 | 1A | metal | |
| Mg | 12 | 2 | 8 | 2 | 3 | 2A | metal | |
| Ca | 20 | 2 | 8 | 8 | 2 | 4 | 2A | metal |
| S | 16 | 2 | 8 | 6 | 3 | 6B | non-metal | |
| F | 9 | 2 | 7 | 2 | 6B | non-metal | ||
1. Mg (12) and Ca are the metals which belong to group 2 in Mendeleev’s periodic table.
2. S (16) and Cl (17) are the non-metals which belong to the 3rd period of Mendeleev’s periodic table.
Question 26. The number of electrons and neutrons in an atom of an element are 17 and 18 respectively. Predict .the position of the element in the Mendeleevas periodic table.
Answer: Number of electrons = 17
Electronic configuration =2,8,7
The elements will belong to 3rd period and Group 8 B in Mendeleev’s periodic table.
Question 27. If the electronic configuration of an element is 2, 8, 8, 1, then answer the following questions
1. Write down the number of periods and groups.
2. Write down the electronic configuration of another element of this group.
Answer:
1. The element belongs to the 4th period and group- 1 in the long form of modern periodic table.
2. Electronic configuration of another element of group-1 is 2, 8,1.
Question 28. A, B, and C are three different elements. B is an inert gas. Their atomic numbers are (Z -1), Z and (Z+l) respectively
1. Except B which one is a non-metal?
2. Which one is definitely a metal?
3. Predict the group-wise position of ‘A’ in the periodic table and the valency of A.
Answer:
1. ‘A’ is definitely a non-metal.
2. ‘C’ is definitely metal.
3. Element ‘A’ belongs to Group 7B in Mendeleev’s periodic table or Group 17 in the long form of the periodic table. Being an element of Gr 17, the valency of A is 1.
Question 29. The atomic numbers of the three elements A, B, and C are 6,8, and 10 respectively. C is an inert gas.
1. Which one is most electronegative?
2. Atomic size is least for which element?
3. In which group does element B reside?
Answer:
The electronic configuration of 6A is K(2), L(A).
The electronic configuration of 8B is K(2), L(6).
Electronic configuration of 10C is K(2),L(8).
1. It is obvious from the electronic configuration that element B is the most electronegative.
2. Atomic size is least for the element B.
3. The element B belongs to the Gr-16 of the modern periodic table. It is a member of the 2nd period.
WBBSE Class 10 Revision Notes on Periodicity
Question 30. The number of electrons in the outermost shell of elements X and Y are 2 and 7 respectively.
1. In which group of periodic table should the elements be placed?
2. Which one is an oxidising agent and which one is a reducing agent in case of forming compounds?
Answer:
1. ‘X’ should be placed in Gr-2 of the modern periodic table as the number of electrons in the valence shell is 2.
‘T’ should be placed in Gr-17 of the modern periodic table as the number of electrons, in the valence shell is 7.
2. ‘Y’ will act as an oxidising agent as it has a tendency to accept electrons.’X’ will act as reducing agent as it has a tendency to lose electrons.
Question 31. The atomic numbers of three elements A, B and C are 9, 10 and 11 respectively.
1. Which element among these is the most electronegative?
2. Metallic character is the highest for which one?
3. What will be the nature of the compound formed by the combination of A and C?
Answer:
| Element | Atomic No. | Electronic configuration | Position in the periodic table | ||||
| K | L | M | N | Period | Group | ||
| A | 9 | 2 | 7 | 2 | 17 | ||
| B | 10 | 2 | 8 | 2 | 18 | ||
| C | 11 | 2 | 8 | 1 | 3 | 1 | |
1. ‘A’ is a most electronegative element.
2. ‘C’ has the highest metallic character.
3. The compound formed by the combination of A and C will be ionic in nature.
Question 32. The atomic numbers of three elements A, B, and C are 3,11 and 19 respectively.
1. Mention the group where the elements are placed in Mendeleev’s periodic table.
2. Metallic character is the highest for which one?
3. What is the nature of the compound formed in the reaction of B and Cl2?
Answer:
| Element | Atomic No. | Electronic configuration | Position in Mendeleev’s table | ||||
| K | L | M | N | Period | Group | ||
| A | 3 | 2 | 1 | 2 | IA | ||
| B | 11 | 2 | 8 | 1 | 3 | IA | |
| C | 19 | 2 | 8 | 8 | 1 | 4 | IA |
1. The elements belong to Gr-1A of Mendeleev’s periodic table.
2. Element ‘C has the highest metallic character.
3. The compound formed by the reaction of B and Cl2 will be ionic in nature.
Question 33. The atomic numbers of the four elements A, B, C, and D are 3, 9/11 and 17 respectively. Which one is the most electropositive element and which one is the most electronegative element?
Answer:
| Element | Atomic No | Electronic configuration | Position in the periodic table | |||
| K | L | M | Period | Group | ||
| A | 3 | 2 | 1 | 2 | 1 | |
| B | 9 | 2 | 7 | 2 | 17 | |
| C | 11 | 2 | 8 | 1 | 3 | 1 |
| D | 17 | 2 | 8 | 7 | 3 | 17 |
‘C’ is the most electropositive and ‘B’ is the most electronegative element among these elements.
Question 34. The atomic numbers of Elements A, B, C and D are 3, 9,11 and 19 respectively.
1. Which one has the highest reducing property? ‘
2. Electronegativity of which one is the highest?
Answer:
| Element | Atomic No. | Electronic configuration | Position in the periodic table | ||||
| K | L | M | N | Period | Group | ||
| A | 3 | 2 | 1 | 2 | 1 | ||
| B | 9 | 2 | 7 | 2 | 17 | ||
| C | 11 | 2 | 8 | 1 | 3 | 1 | |
| D | 19 | 2 | 8 | 8 | 1 | 1 | |
1. Reducing the property of D is the highest.
2. Electronegativity of B is the highest.
Periodic Table and Periodicity in the Properties of Elements Topic B Chemical Periodicity Of Elements Very Short Answer Type Questions Choose The Correct Answer:
Question 1. Moving across a period from left to right, the atomic radii of elements
1. Gradually increases
2. Gradually decreases
3. Remains unchanged
4. Initially increases then decreases
Answer: 2. Gradually decreases
Question 2. On going down a group, the atomic radii of elements
1. Gradually decreases
2. Gradually increases
3. Remains unchanged
4. Initially increases then decreases
Answer: 2. Gradually increases
Question 3. In a given period, with decreasing atomic size of elements, the ionisation energy
1. Increases
2. Decreases
3. Remains unchanged
4. Either increases or decreases
Answer: 1. Increases
Question 4. In a given period, with an increase in nuclear charge of the atom of an element, the ionisation energy
1. Decreases
2. Increases
3. Remains unchanged
4. Either increases or decreases
Answer: 2. Increases
Question 5. The unit of electronegativity is
1. eV
2. erg
3. dyne
4. It is a unitless quantity
Answer: 4. It is a unitless quantity
Question 6. In a given period, the electronegativity is minimum for the elements of
1. Group-1
2. Group-2
3. Group-14
4. Group-17
Answer: 1. Group-1
Question 7. In a given period, the electronegativity is maximum for the elements of the group
1. 16
2. 17
3. 18
4. 14
Answer: 2. 17
Question 8. In a given period, with an increase in the atomic size of an element, its electronegativity will
1. Increase
2. Decrease
3. Increases or decrease
4. Remain unchanged
Answer: 2. Decrease
Question 9. For the elements of 2nd period, the correct order of atomic radii is
1. B > C > N > 0
2. B > N > C > 0
3. B > 0 > N > C
4. N > 0 > B > C
Answer: 1. B > C > N > 0
Question 10. The correct order of atomic radii for alkali metals is
1. Na < Rb < K < Cs
2. Na < K < Rb < Cs
3. K < Na < Cs < Rb
4. Na < Cs < K < Rb
Answer: 2. Na < K < Rb < Cs
Question 11. The least electronegative non-radioactive element is
1. Na
2. K
3. Rb
4. Cs
Answer: 4. Cs
Question 12. For the elements of 2nd period, the correct order of ionisation energy is
1. B < C < N >0
2. B < C < O < N
3. C < B < N > 0
4. N > C < B < 0
Answer: 1. B < C < N >0
Question 13. The correct order of ionisation energy for group-1 elements is
1. Li > K < Rb > Na
2. Li > Na > Rb > K
3. Li > Na > K > Rb
4. Na < Li > Rb > K
Answer: 3. Li > Na > K > Rb
Question 14. The correct order of electronegativity for the following element is
1. Li < Be < C < B
2. Li <Be < B < C
3. Li < B > Be > C
4. Be > Li < B < C
Answer: 2. Li <Be < B < C
Question 15. The correct order of reducing power of the elements in 3rd period is
1. Al < Si > P > S
2. Al > Si > S > P
3. Al > Si > P > S
4. Si < Al > S < P
Answer: 3. Al > Si > P > S
Question 16. The correct order of oxidising power of the halogens is
1. F > Br > Cl > I
2. Cl > F > Br > 1
3. Cl < F < Br < I
4. F > Cl > Br > I
Answer: 4. F > Cl > Br > I
Question 17. Most electronegative element is
1. 0
2. CL
3. F
4. Ne
Answer: 3. F
Question 18. Which one is more electronegative?
1. Na
2. K
3. Rb
4. Cs
Answer: 1. Na
Question 19. Which one of the following has the highest reducing ability?
1. K
2. Na
3. Li
4. Cs
Answer: 4. Cs
Question 20. Which halogen element has the least electronegativity?
1. F
2. Cl
3. Br
4. I
Answer: 4. I
Question 21. Which one is not a periodic property?
1. Oxidising property
2. Reducing property
3. Radioactivity
4. Atomic radius
Answer: 3. Radioactivity
Question 22. Which one of the following has the highest atomic radius?
1. K
2. H
3. Li
4. Na
Answer: 1. K
Question 23. The most oxidising element in second period of the periodic table is
1. F
2. Cl
3. Be
4. O
Answer: 1. F
Question 24. Which of the following alkali metals has the highest atomic radius?
1. Li
2. Na
3. Rb
4. Cs
Answer: 4. Cs
Question 25. Which of the following indicates the atomic number of a Gr-!A element?
1. 13
2. 17
3. 11
4. 10
Answer: 3. 11
Question 26. Which one of the following has the least electronegativity?
1. Ca
2. Mg
3. Sr
4. Ba
Answer: 4. Ba
Question 27. The correct order of reducing power is
1. Na < Al < Si < Mg
2. Na < Mg < Al < Si
3. Si < Al < Na < Mg
4. Si < Al < Mg < Na
Answer: 4. Si < Al < Mg < Na
Periodic Table and Periodicity in the Properties of Elements Topic B Chemical Periodicity Of Elements Answer In Brief:
Question 1. What is meant by ‘periodicity of elements’?
Answer:
‘Periodicity of elements’:
The recurrence of properties of the elements at definite intervals when arranged in increasing order of their atomic numbers is called the periodicity of elements.
Question 2. In the case of the 4th period, after how many elements are properties repeated?
Answer: After 18 elements, in the 19th element properties are repeated.
Question 3. What is meant by the term ‘atomic radius? Classify atomic radius.
Answer:
Atomic radius
It is the distance between the centre of the nucleus and the outermost orbit of an atom. Atomic radius is classified as:
1. Covalent radius,
2. Metallic radius and
3. Van der Waals’ radius.
Word Problems Related to Periodic Properties
Question 4. Define metallic radius.
Answer:
Metallic radius:
Half of the distance between the nuclei of two adjacent metal atoms in a metallic crystal is called the metallic radius.
Question 5. What is van der Waals’ radius?
Answer:
Van der Waals’ radius
Half of the distance between the nuclei of two non-bonded neighbouring atoms of two adjacent molecules of the same substance in solid state is known as van der Waals’ radius.
Question 6. Arrange van der Waals’ radius, metallic radius and covalent radius in decreasing order of their values.
Answer: The decreasing order of the three atomic radii is as follows: van der Waals’ radius > metallic radius > covalent radius.
Question 7. The elements of which group in a given period of the periodic table have the largest atomic radii?
Answer: The elements of group 1 in a given period of the periodic table have the largest atomic radii.
Question 8. Whose atomic radius is smaller—Li or F?
Answer: Atomic radius of F is smaller.
Question 9. Which of the following has the smaller atom — Mg and Al?
Answer: Atoms of Al are smaller than that of Mg.
Question 10. Arrange Be, Na, Ar, S in order of atomic radius.
Answer: Ar > Na > S > Be .
Question 11. Arrange Al, Mg, Cl, Na, P, S and Si in decreasing order of their atomic radii.
Answer: Decreasing order of atomic radii: Nai > Mg > Al > Si > P > S > Cl.
Question 12. How does ionisation energy change across a period?
Answer: From left to right, across a period, the ionisation energy of elements gradually increases.
Question 13. The elements of which group in a given period of the periodic table have the lowest ionisation energy?
Answer: The elements of group 1 in a given period of the periodic table have the lowest ionisation energy.
Question 14. Name the element with highest ionisation energy.
Answer: Helium (He)’.
Question 15. Name the element with the lowest ionisation energy.
Answer: Caesium.
Question 16. Arrange the following elements in increasing order of ionisation energy—Li, Rb, K and Na.
Answer: Rb < K < Na < Li.
Question 17. What is the relation between atomic radii and electronegativity of the elements in a period?
Answer: Smaller the atomic radii of elements in a period, greater will be the electronegativity.
Question 18. Arrange F, Cl, Br and I in decreasing order of electronegativity.
Answer: Decreasing order of electronegativity: F > Cl > Br > I.
Question 19. How does the electronegativity of the Gr-1 elements change from top to bottom?
Answer: From top to bottom of group 1, electronegativity gradually decreases.
Question 20. Mention the position of the most electronegative element in the periodic table.
Answer: The most electronegative element F belongs to the 2nd period and Gr-17 in the periodic table.
Question 21. Arrange Na, Mg, Al, Cl and P is increasing order of electronegativity.
Answer: Na < Mg < Al < P < Cl.
Question 22. Arrange the following elements in increasing order of electronegativity—Na, O, N, F.
Answer: Na < N < 0 < F.
Question 23. Arrange Li, Be, B, N in decreasing order of electronegativity.
Answer: N > B > Be > Li.
Question 24. What is the relation between ionisation energy and electronegativity?
Answer: The ionisation energy of an element increases with the increase in electronegativity.
Question 25. What is the relation between ionisation energy and the reducing property of an element?
Answer: Lower the ionisation energy of an element, the stronger will be its reducing power.
Question 26. What is the relation between electronegativity and oxidising property of an element?
Answer: Higher the electronegativity of an element, the stronger will be its oxidising power.
Question 27. An element A is positioned in group 13 of the periodic table. What is the formula of its chloride?
Answer: The valency of all elements of group 13 is 3. Hence, the formula of the chloride of element A will be ACI3.
Question 28. Which elements among the halogens exhibit highest and lowest metallic property?
Answer: Among the halogens, iodine exhibits highest metallic properties while fluorine exhibits the lowest metallic properties.
Question 29. Arrange Si, Mg, P, Al, Na, S and Cl in increasing order of their oxidising power.
Answer: Increasing order of oxidising power: Na < Mg < Al < Si < P < S < Cl.
Question 30. Arrange Na/ K, Rb and Cs in increasing order of electro-positivity.
Answer: Increasing order of electro-positivity: Na < K < Rb < Cs.
Question 31. Elements of which group in the periodic table has the highest oxidising power?
Answer: Elements of group 17 of the periodic table have the highest oxidising power among the elements of the corresponding period.
Question 32. Name the strongest oxidising agent of 2nd period.
Answer: Fluorine (F) is the strongest oxidising agent of 2nd period.
Question 33. Name the element with highest reducing ability of Gr-1 in the long form of the periodic table.
Answer: Lithium (Li).
Question 34. Arrange the halogens in increasing order of reducing power.
Answer: F < Cl < Br < I.
Question 35. Arrange in decreasing order of reducing property—K, Na, Li, Rb.
Answer: Rb < K < Na> Li.
Question 36. Arrange Cl, Br, I, F in increasing order of oxidising property.
Answer: I < Br < Cl < F.
Question 37. Arrange in decreasing order of oxidising property—Al, O, F, Cl.
Answer: F > O > Cl > Al.
Question 38. Among Na, K, O and N which one is the strongest oxidising agent and strongest reducing agent?
Answer: Strongest oxidising agent is O and strongest reducing agent is K.
Question 39. Give an example of a halogen that has reducing property.
Answer: Iodine.
Question 40. Arrange the following elements in increasing order of metallic character- 11 Na, K, Rb, Cs and 0 Br, F, Cl, I.
Answer: Na < K < Rb < Cs and 0 F < Cl < Br < I
Question 41. Arrange the following in increasing order of metallic character—Mg, Na, Al, S, Si, Cl, P.
Answer: Cl < S < P < Si < Al < Mg < Na.
Periodic Table and Periodicity in the Properties of Elements Topic B Chemical Periodicity Of Elements Fill In The Blanks:
Question 1. _________is not a periodic property of elements.
Answer: Radioactivity
Question 2. In a given period the ______ have the smallest atomic radii.
Answer: Halogens
Question 3. The atomic radii of noble gases in a given period is ________ than the atomic radii of halogen atoms.
Answer: Greater
Question 4. The minimum energy required to remove the most loosely bound electron in the outermost orbit of the atom of an element is known as ________ energy of the element.
Answer: Ionisation
Question 5. The electronegativity of elements is measured in ______ scale.
Answer: Pauling
Question 6. The element _________ is the strongest oxidising agent.
Answer: Fluorine
Question 7. The higher the _________ of an element, the stronger will be its oxidising power.
Answer: Electronegativity
Question 8. Noble gases being ________ their covalent radii cannot be measured.
Answer: Mono-atomic
Question 9. The greater the tendency of an element to accept an electron greater will be its property and the greater the tendency of an element to release an electron, the greater will be its _______ property.
Answer: Oxidising, reducing
Question 10. The atomic radius of Al is ________ than SI.
Answer: Greater
Question 11. The ionisation potential of oxygen is _______ than that of nitrogen.
Answer: Less
Question 12. The ________ power of Na is less than that of Si.
Answer: Oxidising
Question 13. The reducing power of caesium is _______ than that of rubidium.
Answer: More
Question 14. The magnetic property of elements is not a ________ property.
Answer: Periodic
Question 15. Across a period from left to right atomic radius of elements gradually _______
Answer: Decreases
Question 16. Among all elements, atomic radius is the least in the case of _______
Answer: Hydrogen
Question 17. Among Al, S, Si and P, element with the highest electronegativity is _________
Answer: S
Question 18. The most reactive non-metal is _______
Answer: Fluorine
Periodic Table and Periodicity in the Properties of Elements Topic B Chemical Periodicity Of Elements State Whether True Or False:
Question 1. A covalent radius is always greater than a metallic radius.
Answer: False
Question 2. The correct order of atomic size is— F < Cl < Br < I < At
Answer: False
Question 3. The greater the size of an atom of an element, the greater will be its electronegativity.
Answer: False
Question 4. In the measurement of the electronegativity of different elements by the Pauling scale, the electronegativity of hydrogen is taken as 2.1.
Answer: True
Question 5. The increasing order of electropositivity is Na < K < Rb < Cs
Answer: True
Question 6. Mendeleev emphasized mainly on chemical and physical properties of elements while constructing the periodic table.
Answer: True
Question 7. Down a group atomic size of an element gradually decreases.
Answer: False
Question 8. Ionisation energy decreases with an increase in atomic size.
Answer: True
Question 9. Down a group metallic character decreases and oxidising power increases.
Answer: False
Question 10. Across a period, from left to right oxidising property decreases.
Answer: False
Question 11. Halogen elements are strong reducing agents.
Answer: False
Question 12. Order of reducing power— F > Cl > Br > I.
Answer: False
Question 13. If the number of electrons in the valence shell is 3, then the position of element in the long form of periodic table will be in group 13.
Answer: True
Periodic Table and Periodicity in the Properties of Elements Miscellaneous Type Questions Match The Columns:
Question 1.
| Column A | Column B |
| Transition element | 1. He |
| Coinage metal | 2. H2 |
| Inert gas | 3. Fe |
| Rogue element | 4. Ag |
Answer:
Transition element: 3. Fe
Coinage metal: 4. Ag
Inert gas: 1. He
Rogue element: 2. H2
Question 2.
| Column A | Column B |
| Alkaline earth metal | 1. Te |
| Chalcogen | 2. Rb |
| Representative element | 3. Xe |
| Bridge element | 4. Ra |
Answer:
Alkaline earth metal: 4. Ra
Chalcogen: 1. Te
Representative element: 2. Rb
Bridge element: 3. Xe
Question 3.
| Column A | Column B |
| Highest electronegativity | 1. Fe |
| Highest reducing power among group-1 elements | 2. F |
| Variable oxidation state | 3. He |
| Highest ionisation energy | 4. Cs |
Answer:
Highest electronegativity: 2. F
Highest reducing power among group-1 elements: 4. Cs
Variable oxidation state: 1. Fe
Highest ionisation energy: 3. He
WBBSE Solutions for Class 10 Physical Science and Environment
- Chapter 1 Environmental Concern
- Chapter 2 Behaviour of Gases
- Chapter 3 Chemical Calculations
- Chapter 4 Phenomena of Heat
- Chapter 5 Light
- Chapter 6 Current Electricity
- Chapter 7 Atomic Nucleus
- Chapter 8 Physical and Chemical Properties of Elements