Ionic and Covalent Bonds Topic A Electronic Concept of Valency, Ionic Bonding, and Properties of Ionic Compounds Synopsis
WBBSE Class 10 Ionic and Covalent Bonds Overview
Chemical bond
The force of attraction which holds two of more constituents (atoms, ions, etc.) together in different chemical species is known as a chemical bond. It is formed either by losing or gaining electrons or by sharing pairs of electrons.
Octet rule: To attain chemical stability, an atom tends to acquire stable electronic configuration of the nearest noble gas, i.e., tends to attain 8 electrons in its outermost shell either by gaining or losing electrons or by sharing pairs of electrons. This tendency to acquire 8 electrons in the outermost shell of the atoms is called octet rule. There are many compounds where the constituent atoms do not follow the octet rule.
Wbbse Class 10 Physical Science Notes
Duplet rule: The elements near helium (H, Li, Be ) in the periodic table try to attain the stable electronic configuration of He by gaining, losing or sharing electrons in their outermost shells. This tendency to acquire 2 electrons in the outermost shell of atoms is called duplet rule.
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Electrovalency: To achieve stable electronic configuration of the nearest noble gas, some atoms completely give up one or more electrons from their outermost shell to form stable cations while some other atoms gain these electrons to form stable anions.
These two oppositely charged ions then combine together through the electrostatic force of attraction to form chemical compounds. The capacity of the elements for such chemical combination is known as electrovalency or ionic valency.
The bond formed between the atoms due to electrovalence is called an electrovalent bond or ionic bond and the compound formed in this way is called electrovalent or ionic compound.
Characteristics of ionic compounds: Ionic compounds do not exist as discrete molecules. They are solid crystalline substances with high melting and boiling points. They do not conduct electricity in solid state but are good conductors in a molten state or in an aqueous solution. Ionic compounds are soluble in polar solvents and react very fast in solution.
The term ‘molecular mass’ is not applicable for ionic compounds as they do not exist in molecular form. Instead, the formula mass of these compounds is determined. For covalent compounds, both molecular and formula mass are the same.
Wbbse Class 10 Physical Science Notes
In NaCI crystal, a large number of Na+ and Cl– ions remain closely packed by a strong electrostatic force of attraction. This leads to the formation of stable three-dimensional crystal lattices.
Electron structure of NaCI:
Electron structure of CaO:
Electron structure of MgCI:
Examples of electrovalent compounds include calcium oxide, magnesium chloride, sodium fluoride, lithium hydride, etc. In it, the outermost shell of each constituent atom contains one electron.
Ionic and Covalent Bonds Topic A Electronic Concept of Valency, Ionic Bonding, and Properties of Ionic Compounds Short And Long Answer Type Questions
Question 1. Why do atoms of different elements react With each other?
Answer: The electronic configuration of the noble gases are very stable. To attain the electronic configuration of the nearest noble gases, atoms of different elements react with each other.
Question 2. Define chemical bond.
Answer:
Chemical bond:
The force of attraction which holds two or more constituents (atoms, ions etc.) together, different chemical species is .called chemical bond. It is formed either by losing or gaining electrons or by sharing pairs of electrons by atoms.
Wbbse Class 10 Physical Science Solutions
Question 3. What is the octet rule?
Answer:
Octet rule:
To attain chemical stability, an atom tends to acquire stable electronic configuration of the nearest noble gas either by gaining or losing electrons or by sharing pairs of electrons of its outermost shell. This tendency to acquire 8 electrons in the outermost shell of an atom is called the octet rule.
Question 4. state the limitations of octet rule.
Answer:
Octet rule has certain limitations. These are:
1. In some compounds, the central atom has more or less than 8 electrons, yet the molecules are highly stable. The Octet rule fails to explain this.
2. Octet rule is based on the stability and inertness of noble gases. But some noble gases specifically Xe form compounds with oxygen and fluorine.
3. This rule cannot explain the relative stability of different molecules.
Question 5. The octet rule is not always followed in case of ionic compounds. Give examples.
Answer:
The octet rule is not always followed in case of ionic compounds
The stability of ionic compounds cannot be always explained by octet rule. In case of transition metals, it is observed that octet rule is not followed. For example, in FeCl2, Fe2+ ion has 14 electrons in its valence shell, and in FeCI3, the Fe3+ ion has 13 electrons in its valence shell.
In both cases, octet rule is violated. Again, in LiH, h u+ ion and H~ ion have 2 electrons in their valence shells. Hence, octet rule is not valid for all ionic compounds.
Question 6. Show with an example that compounds can be formed without fulfillment of octet of the corresponding ions.
Answer: The stability of all ionic compounds can not be explained with the concept of sharing 8 electrons in the valence shell of the constituting ions, or the octet rule, e.g., in LiH the constituting ions Li⊕ and HΘ both have 2 electrons in their valence shell.
Moreover, in case of elements showing variable electrovalency, especially in transition metals octes rule is not obeyed in many instances. E.g., in FeCl2 or FeCI3, octet rule is not obeyed in Fe2+ and Fe3+.
Question 7. What is duplet rule?
Answer:
Duplet rule:
To attain chemical stability an atom of an element nearer to He (H, Li, Be) tends to acquire stable electronic configuration like He either by gaining or losing electrons or by sharing electron pairs of its outermost shell. This tendency to acquire 2 electrons in the outermost shell of an atom is called duplet rule.
Wbbse Class 10 Physical Science Solutions
Question 8. Which type of chemical bond is formed by complete transfer of electron from one atom to another atom? Explain with an example.
Answer:
1. Ionic bond or electrovalent bond is formed by complete transfer of electron from one atom to another atom.
2. Magnesium (electronic configuration: 2, 8, 2) loses 2 valence electrons to form an Mg2+ ion and attains the stable electronic configuration of nearest inert gas. On the otherhand oxygen (electronic configuration: 2, 6) accepts these two electrons to form O2- ion and attains the stable electronic configuration of the nearest inert gas.
Therefore when Mg and O atoms combine, the former transfers its valence electron to the latter resulting in the formation of Mg2+ and O2- respectively. The two ions are then held together by strong electrostatic forces of attraction to form MgO.
Question 9. Define electrovalency.
Answer:
Electrovalency:
To achieve the stable electronic configuration of nearest noble gas, some atoms give up one or more electrons from the outermost shell completely to form stable cations while some other atoms gain these electrons to form stable anions. These two types of oppositely charged ions combine together through electrostatic force of attraction to form chemical compounds. The capacity of the elements for such chemical combination is known as electrovalency.
Question 10. How is the electrovalency of an atom measured? Explain with example.
Answer:
1. The number of electrons gained or released by an atom during the formation of an ionic compound is measured as the electrovalency of that atom.
2. For example, during formation of NaCl, a Na – atom releases one electron to form a Na+ ion while a Cl – atom accepts that electron and converts it to Cl– ion. Hence, the electrovalency of both sodium and chlorine in NaCl is 1.
Question 11. Ionic bonds are not real bonds- Justify the statement.
Answer:
Ionic bonds are not real bonds:
In covalent compounds, two atoms share one or more pairs of electrons with each other to form bonds having definite directions. But, in electrovalent compounds, the bond between two atoms is formed due to the strong electrostatic force of attraction between the cations and the anions. Here, no electron pair is shared by the involved ions. That is why ionic bonds are not considered as real bond.
Understanding Ionic Bonds: Formation and Properties
Question 12. State two important characteristics of ionic bond.
Answer:
An ionic bond shows the following characteristics:
1. An ionic bond is formed between atoms of an electropositive and an electronegative element.
2. Ionic bond is in fact an electrostatic force of attraction between oppositely charged ions. So, sometimes, it is not considered, as a real bond.
Wbbse Class 10 Physical Science Solutions
Question 13. Write down some properties of ionic compound.
Answer:
Some properties of ionic compound:
1. Ionic compounds form crystals of definite geometrical shape.
2. The melting and boiling points .of ionic compounds are generally very high.
3. Ionic bond is non-directional in nature.
4. Ionic compounds do not exhibit isomerism.
5. Ionic compounds do not conduct electricity in the solid state, but in the molten state or in solution in a suitable solvent (like water) conduct electricity.
6. Ionic compounds generally dissolve in polar solvents.
Question 14. Why any ionic compound possesses high boiling point and melting point?
Answer: In ionic compounds, the oppositely charged ions are held together by strong electrostatic force of attraction. The mutual attraction between large number of oppositely charged ions results in the formation of large crystal lattices. Separation of ions from these crystal lattices requires large amount of energy. Hence, ionic compounds possess high melting and boiling points.
Question 15. Discuss the physical state of ionic compounds.
Answer:
The physical state of ionic compounds:
At normal temperature and pressure all ionic compounds are crystalline solids. This is because the oppositely charged ions are held together by strong electrostatic force of attraction which results in the formation of regular three-dimensional network called crystal lattice. Ionic compounds do not exist as discrete molecules.
Question 16. Why are ionic compounds hard in nature?
Answer: In ionic compounds, large number of oppositely charged ions are held together by strong electrostatic force of attraction which results in the formation of large crystal lattices. The ions remain closely packed in the crystal and the intermolecular space between them is very small. The hardness of an ionic compound is due to the aggregation of large number of ions in a very small space.
Question 17. Ionic compounds conduct electricity in molten state or in aqueous solutions but are non-conductors in the solid state. Explain with reason.
Answer:
Ionic compounds conduct electricity in molten state or in aqueous solutions but are non-conductors in the solid state.
In solid state, the cations and anions in an ionic compound are held together by a strong electrostatic force of attraction. Hence, the ions are immobile and the compound fails to conduct electricity in solid state.
However, when the compound is in a molten state or is dissolved in water, the crystal lattice breaks, and the ions are separated. Due to presence of such mobile ions, ionic compounds conduct electricity in a molten state or in an aqueous solution.
Wbbse Class 10 Physical Science Solutions
Question 18. Discuss with example the solubility of ionic compounds.
Answer: Ionic compounds are generally soluble in polar solvents (such as water), but are insoluble in nonpolar solvents (such as CH2, CCI4, benzene, etc). For example, NaCI is soluble in water but insoluble in benzene.
Question 19. Why does the reactions involving ionic compounds occur at a faster rate?
Answer: Reactions of ionic compounds generally take place in solutions. In solution, the ionic compounds dissociate to form ions that take part in the reaction. Due to the participation of the ions, the reactions occur at a faster rate.
Question 20. Explain why ionic compounds are soluble in polar solvents.
Answer: When an ionic compound is dissolved in a polar solvent, the negatively charged end of the polar solvent attracts the cations present in the crystal lattice of the solid. Similarly the positive end of the solvent attracts the anions.
This attraction by the solvent molecules decreases the force of attraction between cations and anions in the crystal lattice. Hence the dissociated ions are separated and are surrounded by solvent molecules in solution to get stabilised. This is why ionic compounds are soluble in polar solvents.
Question 21. Why are ionic compounds insoluble in non-polar solvents?
Answer: The molecules of a non-polar solvent cannot attract the ions of an ionic compound effectively. Hence, ionic compounds do not generally dissociate in non-polar solvent. That is why ionic compounds are generally insoluble in non-polar solvents.
Question 22. A compound has high boiling and melting point. It does not conduct electricity in solid state but is a good conductor in solution. Which type of bond is present in the compound? What is the nature of the constituent particles of the compound?
Answer:
1. The compound is an ionic or electrovalent compound. So, ionic bond is present in it.
2. The compound is composed of cations and anions.
Question 23. Describe the formation of NaCI.
Answer:
The formation of NaCl
Electronic configuration of Na-atom is K = 2, L = 8, M = 1, and that of chlorine is K= 2, L = 8, M = 7. When sodium reacts with chlorine, 1 electron from the outermost shell of a sodium atom is transferred to a chlorine atom. As a result, Na+ and Cl– ions are formed. These ions combine by the electrostatic force of attraction to from NaCl.
Covalent Bonds Explained with Examples
Question 24. Why the bond of sodium chloride can not be expressed as Na — Cl?
Answer: Na-atom loses its valence electron to form Na+ cation and Cl– atom accepts it to form Cl– anion. Na+and Cl– ions are then held together by strong electrostatic forces of attraction to form the electrovalent compound NaCI. Here no electron pair is formed and this force of attraction has no definite direction. So it can be said that the bond of sodium chloride can not be expressed as Na—Cl.
Question 25. Describe the nature of bond present in CaO.
Answer:
The nature of bond present in CaO:
Electronic configuration of Ca-atom is K= 2, L = 8, M = 8, N = 2 and that of oxygen is K = 2, L = 6 . When calcium reacts with oxygen, Ca-atom releases 2 electrons from its outermost shell to form Ca2+ ion and acquire the stable electronic configuration of the nearest noble gas Ar [K = 2, L = 8, M = 8).
Similarly, oxygen atom accepts those electrons to form O2- ion and attains the electronic configuration of neon [K = 2, L= 8). Ca2+ ions and O2- ions then combine by electrostatic force of attraction to form crystals of CaO. Hence the bond in CaO is ionic.
Wbbse Class 10 Physical Science Solutions
Question 26. Describe the formation of MgCI2.
Answer:
The formation of MgCI2
Electronic configuration of Mg-atom is K = 2, L = 8, M = 2, and that of chlorine is K = 2, L = 8, M = 1. When magnesium reacts with chlorine, an Mg-atom releases 2 electrons from its outermost shell to form an Mg2+ ion and acquire the electronic configuration of the nearest noble gas Ne (K = 2, L = 8).
On the other hand, two Cl-atoms accept one electron each to form two Cl– ions, and each Cl– ion attains the electronic configuration of Ar [K= 2, L = 8, M = 8). Mg2+ ions and two Cl– ions combine by the electrostatic force of attraction to form MgCI2. In the MgCI2 crystal, Mg2+ and Cl– ions are present in 1: 2 ratio.
Question 27. Describe how NaF is formed?
Answer: Electronic configuration of the Na-atom is K-2, L – 8, M = 1, and that of the F-atom is K = 2, L = 7. When Na reacts with F, a Na-atom releases 1 electron from its outermost shell to form a Na+ ion and acquire the electronic configuration of the nearest noble gas Ne {K = 2, L = 8). An F -atom accepts this electron to form F“ ion and attains the electronic configuration of Ne [K = 2, L = 8). These ions combine by the electrostatic force of attraction to form NaF.
Question 28. Describe the nature of bond present in LiH.
Answer:
The nature of bond present in LiH:
Electronic configuration of Li-atom is K= 2, L = 1, and that of hydrogen is K = 1, When Li reacts with H, 1 electron is transferred from the outermost shell of Li to the outermost shell of hydrogen. Due to loss of an electron, Li is converted to Li+ ion while hydrogen becomes H– ion by accepting the electron.
Both of them attain the electronic configuration of their nearest noble gas helium (K = 2). Oppositely charged Li+ and H– ions combine through electrostatic force of attraction to form ionic bond.
Question 29. Three elements X, Y, and 2 have atomic numbers 6, 9, and 12 respectively.
1. Which elements among them will form an anion and cation?
2. Which type of bond will be formed between Y and Z when they chemically combine with each other?
Answer:
Element | X | Y | z |
Atomic number | 6 | 9 | 12 |
Electronic configuration | 2,4 | 2,7 | 2,8,2 |
1. Y has only one electron short of the stable electronic configuration of its nearest noble gas. Hence, it will easily form an anion by accepting an electron. Z has two electrons in its outermost orbit. So, it can easily release these two electrons to form a Z2+ cation.
2. Y is an electronegative element and Z is an electropositive element. Hence, the bond formed between Y and Z will be ionic in nature. The electrovalency of Z is 2 and that of Y is 1. Hence the formula of the compound will be ZY2.
Wbbse Class 10 Physical Science Solutions
Question 30. Complete the following table:
Element | Na | P | C |
Formula of chloride | |||
Nature of bond | |||
The physical state of chloride |
Answer:
Element | Na | P | C |
Formula of chloride | NaCI | PCI3,PCI5 | CCI4 |
Nature of bond | Ionic | Covalent, covalent | Covalent |
The physical state of chloride | Solid | Liquid, liquid | Liquid |
Question 31. Electronic configuration of two elements M and N are 2, 8, 1, and 2,7 respectively. By which type of valency will the atoms combine to form compound? What will be the probable formula of the compound?
Answer:
1. It is obvious from the electronic configurations that element M has a tendency to lose an electron from its valence shell to attain the stable electronic configuration and form M+ cation. On the other hand element, N has the tendency of accepting the electron in its valence shell to attain the stable electronic configuration and form N– anion.
Therefore M+ and N– ions will held together by strong electrostatic force of attraction and form compound by electrovalency.
2. The probable formula of the compound will be MN.
Question 32. Electronic configuration of two elements A and B are K(2) 1(7) and K(2) L(8) M(2) respectively. By which type of valency they will combine to form the compound? What will be the formula of the compound.
Answer:
1. Element B will lose 2 electrons to attain the stable electronic configuration and form a B cation while two atoms of elements A will accept one electron each for attaining the stable electronic configuration and form two A– anions.
These ions will be hold together by strong electrostatic force of attraction to form the compound. Therefore by electrovalency or ionic valency, they will combine to form compound.
2. Formula of the compound will be BA2.
Question 33. Which one between NaCI and CHCL3 will form a white precipitate by reacting with AgNO3?
Answer: NaCI is an ionic compound. Hence it dissociates in aqueous solution to form Na+ and Cl– ions. Due to the presence of free chloride ions in aqueous solution, it reacts with AgNO3 to produce white precipitate of AgCl.
But CHCL3 does not produce chloride ions in aqueous solution. Hence, it will not produce any precipitate when reacted with AgNO3.
Question 34. An element X combines with oxygen to form a compound X2O. If the molten oxide conducts electricity, then
1. In which group of the periodic table does the element X belong to?
2. what will be the nature and formula of the chloride if X combines with chlorine?
Answer: The molten oxide conducts electricity. Hence, the compound X2O is an ionic compound. As O is electronegative, X must be an electropositive element.
1. X should be present in . group IA of Mendeleev’s periodic table.
2. Chlorine is electronegative and X is an electropositive element. Hence, ionic bond will be formed between them. The formula of the compound will be XCI.
Question 35. Sodium is a highly reactive metal which reacts with water violently. Chlorine is also a highly reactive non-metal having strong oxidising property. But the compound NaCI is safely used as common salt. Explain with reason.
Answer: Ions are generally more stable than free atoms. During chemical combination, Na-atom loses one electron to form Na+ ion while Cl – atom easily accepts that electron to form Cl– ion. Both Na+ and Cl– ions have stable electronic configurations of their nearest noble gases.
In case of NaCI, a large number of Na+ and Cl– ions aggregate together to form crystals of NaCI. So, free atoms of sodium and chlorine are not present in NaCI and hence the compound is not as much reactive as free sodium and chlorine atoms. Hence, we can safely use NaCI as common salt.
Question 36. When an aqueous solution of NaCI is added to a solution of AgNO3 the reaction takes place at a very fast rate. Explain why.
Answer: In the reaction between NaCI and AgNO3, AgCI is precipitated out. It is insoluble in water as well as in acid. Both NaCI and AgNO3 are ionic compounds. In aqueous solution, both the compounds completely dissociate into ions. These ions react with each other at a very faster rate in the solution. Hence ionic reactions take place rapidly.
\(\begin{gathered}\mathrm{AgNO}_3(a q) \rightarrow \mathrm{Ag}^{+}(a q)+\mathrm{NO}_3^{-}(a q) \\
\mathrm{NaCl}(a q) \rightarrow \mathrm{Na}^{+}(a q)+\mathrm{Cl}^{-}(a q) \\
\mathrm{NaCl}(a q)+\mathrm{AgNO}_3(a q) \rightarrow \mathrm{AgCl}^2+\mathrm{NaNO}_3(a q)
\end{gathered}\)
Question 37. Atomic number of two elements A and B are respectively 19 and 17. Which type of compound will be formed between A and B? Justify your answer.
Answer: Electronic configuration of A is K =2, L = 8, M = 8, N = 1, and electronic configuration of B is K = 2, Z. = 8, M = 7.
From the electronic configurations, it can easily be understood that A has a strong tendency to release a single electron from its outermost shell to acquire the stable electronic configuration of Ar. Hence A will easily form A+ ion.
On the other hand, B has only one electron short from the stable electronic configuration of the nearest noble gas. So, it will show strong tendency to accept an electron to form B– ion. These ions will bind by electrostatic force of attraction to form an ionic compound AB.
Ionic and Covalent Bonds Topic A Electronic Concept of Valency, Ionic Bonding, and Properties of Ionic Compounds Very Short Answer Type Questions Choose The Correct Answer
Question 1. At normal temperatures, ionic compounds exist as
- Solids
- Liquids
- Gases
- Crystalline solids
Answer: 4. Crystalline solids
Question 2. The solubility of ionic compounds are higher in
- Water
- Alcohol
- Benzene
- Ether
Answer: 1. Water
Question 3. In aqueous solution, the crystals of ionic solid dissociates to release
- Molecules
- Atoms
- Cations
- Both cations and anions
Answer: 4. Both cations and anions
Question 4. Which of the following has the highest boiling point?
- Sugar
- Naphthalene
- Wax
- NaCI
Answer: 4. NaCI
Question 5. Which of the following, though ionic, is insoluble in water?
- CuSO4
- CH3COOH
- NaNO3
- CaCO3
Answer: 4. CaCO3
Question 6. An example of a polar solvent is
- Benzene
- Ether
- Chloroform
- Water
Answer: 4. Water
Question 7. Which of the following is not characteristic of an ionic compound?
- High melting point
- Electrical conductivity in fused state
- Consist of oppositely charged ions
- Constituent ions form crystal lattice fused state
Answer: 4. Constituent ions form crystal lattice fused state
Question 8. The bond formed between the elements of group-1 (except H) and group-17 of the periodic table is
- Ionic
- Covalent
- Coordinate
- Polar covalent
Answer: 1. Ionic
Question 9. The idea of ionic bond was given by
- Dalton
- Lewis
- Kossel
- Avogadro
Answer: 3. Kossel
Question 10. The term ‘formula mass’ is applicable for
- CH4
- CaCl2
- H2O
- CH3COOH
Answer: 2. CaCl2
Question 11. In which of the following compounds, the metal ion has an incomplete octet?
- LiH
- NaCI
- CaO
- MgCI2
Answer: 1. LiH
Question 12. The electrovalency of Fe in ferrous compounds is
- 3
- 1
- 2
- 4
Answer: 3. 2
Question 13. An element has 2 electrons in its outermost shell. Which of following statements is correct for the element?
- The element will form cation
- The element will form anion
- The element is capable of forming both cation and anion
- The element will not form ions
Answer: 1. The element will form cation
Question 14. An element has 6 electrons in its outermost shell. The element will
- Form cation
- Form anion
- Form both cation and anion
- Not form ions
Answer: 2. Form anion
Question 15. Between Na and Na+, which one has a filled octet?
- Na
- Na+
- Both Na and Na+
- None of these
Answer: 2. Na+
Question 16. Which one among O, O– and O2- most stable?
- O
- O–
- O2-
- All are of equal stability
Answer: 3. O2-
Question 17. The electronic configuration of Li+ resembles which of the following noble gas?
- He
- Ne
- Ar
- Kr
Answer: 1. He
Question 18. The electronic theory of valency was proposed by
- Lewis and Kossel
- Born and Haber
- Proust
- Avogadro
Answer: 1. Lewis and Kossel
Question 19. The nature of bond present in a compound consisting of molecules will be
- Ionic
- Electrovalent
- Covalent
- Metallic
Answer: 3. Covalent
Question 20. In liquid state, a compound comprised of molecules
- Is ionic
- Is electrolytic
- Conducts electricity
- Does not conduct electricity
Answer: 4. Does not conduct electricity
Question 21. An ionic compound used in our daily life is
- Common salt
- Water
- Sugar
- Kerosene
Answer: 1. Common salt
Question 22. The atomic number of elements A, B, and C are respectively (Z- 2), Z, and (Z + 1). If B is a noble gas, the formula of compound formed by A and C will be
- CA2
- CA
- C2A3
- C2A
Answer: 4. C2A
Question 23. Which of the following electrovalent compounds is least soluble in water?
- NaCI
- AgCI
- NaBr
- Nal
Answer: 2. AgCI
Question 24. The non-directional bond is
- Covalent bond
- Coordinate bond
- Electrovalent bond
- All of these
Answer: 3. Electrovalent bond
Question 25. Which one of the following does not conduct electricity?
- Molten NaOH
- Molten KOH
- Solid NaCI
- Molten NaCI
Answer: 3. Solid NaCI
Question 26. Which one is an ionic compound?
- HCI
- CH4
- MgCI2
- NH3
Answer: 3. MgCI2
Question 27. If the atomic number of two elements X and Y be 11 and 17 respectively, then the formula of the compound formed with them
- XY
- X2Y
- XY2
- X2Y3
Answer: 1. XY
Question 28. In the compound LiH, both/Li’ and ‘H’ atom have attained the electronic configuration of the inert gas as in
- Ar
- He
- Ne
- Kr
Answer: 2. He
Question 29. The values of electronegativity of A and B are 1.2 and 3.5 respectively. What will be the nature of chemical bond formed between them?
- Covalent
- Coordinate
- Metallic bond
- Ionic bond
Answer: 3. Metallic bond
Question 30. Which of these does not exist in molecular form?
- CO2
- CH4
- NaCl
- SO2
Answer: 3. NaCl
Question 31. Solid form of which compound is made up of ions?
- Sodium chloride
- Hydrogen chloride
- Naphthalene
- Glucose
Answer: 1. Sodium chloride
Ionic and Covalent Bonds Topic A Electronic Concept of Valency, Ionic Bonding, and Properties of Ionic Compounds Answer In Brief
Question 1. What happens when electricity is passed through an aqueous solution of an ionic compound?
Answer: Electrolysis takes place when electricity is passed through an aqueous solution of an ionic compound, resulting in the formation of new substances at the anode and cathode.
Question 2. Mention the nature of force that operates between constituents of an ionic compound and water molecules in an aqueous solution.
Answer: Electrostatic force of attraction operates between constituents of an ionic compound and water molecules in aqueous solution.
Question 3. If an electron is transferred from one atom to another what will be the nature of valency?
Answer: Transfer of an electron from one atom to another result in electrovalency.
Question 4. Between magnesium chloride and naphthalene, which one conducts electricity in a molten state?
Answer: Magnesium chloride, being an ionic compound, conducts electricity in molten state.
Question 5. In MgCI2, the electronic configuration of the constituent ions resembles which noble gases?
Answer: In MgCI2, electronic configuration of magnesium and chlorine ions resembles the electronic configuration of neon and argon respectively.
Differences Between Ionic and Covalent Bonds
Question 6. What are valence electrons?
Answer:
Valence electrons
The electrons present in the outermost shell of an atom of an element takes part in bond formation. These electrons are known as valence electrons.
Question 7. Who discovered noble gases?
Answer: Scientists Ralley and Ramsay discovered noble gases.
Question 8. Find the formula mass of sodium chloride.
Answer: The formula mass of sodium chloride is (23 + 35.5) = 58.5
Question 9. The atomic number of an element is 12. What type of bond will it form with chlorine?
Answer: It will form electrovalent bond with chlorine.
Question 10. The atomic number of an element is 9. What type of bond will it form with sodium?
Answer: It will form ionic bond with sodium.
Question 11. Name the atom with which the electronic configuration of hydride ion is identical.
Answer: The electronic configuration of the hydride ion is identical with that of a helium atom.
Question 12. What is the similarity between O2- ion, and Ne-atom?
Answer: Both O2- ion and Ne-atom contain 10 electrons and hence they have identical electronic configurations, i.e., they are isoelectronic species.
Question 13. Name an electropositive element that forms both ionic as well as covalent compounds.
Answer: Hydrogen forms both ionic as well as covalent compounds.
Question 14. Write the formula of the compound formed between elements X and Y placed in group 2 and group 17 respectively in periodic table.
Answer: The formula of the compound will be XY2.
Question 15. What is an electrovalent bond?
Answer:
Electrovalent bond
The bond formed between the atoms due to electrovalence is called an electrovalent bond or ionic bond.
Question 16. Name an ionic compound in which the electrovalency of both the anion and cation is 3.
Answer: Aluminium nitride (AIN)
Question 17. A metallic element M forms an ionic oxide MO. How many electrons are present in the valence shell of the M- atom?
Answer: The valency of the metal M is 2. Hence it contains 2 electrons in its valence shell.
Question 18. Give example of an ionic compound where the octet rule is not applicable.
Answer: Lithium hydride (LiH).
Question 19. Give example of a stable cation in which octet is not fulfilled.
Answer: Li+.
Question 20. Write down the number of valence electrons of alkali metals and halogens.
Answer: Number of valence electrons in alkali metals and halogens are 1 and 7 respectively.
Question 21. In which type of compound molecule does not exist?
Answer: Ionic compound.
Question 22. How manyelectrons are present in the valence shell of Ca?
Answer: 2 electrons.
Question 23. Which type of chemical bond is present in CaO?
Answer: Ionic bond.
Question 24. Which type of bond is present in CaCl2.
Answer: Ionic bond.
Question 25. Atomic number of an element is 12. which type of compound will be formed by its reaction with chlorine?
Answer: Ionic compound will be formed.
Question 26. Atomic number of an element is 9. Which type of compound will be formed by its reaction with sodium?
Answer: Ionic compound will be formed.
Question 27. Which type of bond will be formed between A (2, 8, 2) and B (2, 8,7)?
Answer: Ionic bond will be formed between A and B.
Ionic and Covalent Bonds Topic A Electronic Concept of Valency, Ionic Bonding, and Properties of Ionic Compounds Fill In The Blanks
Question 1. Ionic compounds are generally ________ and their crystals have a definite _____ shape.
Answer: Solid, geometrical
Question 2. The crystals of ionic compounds are formed by a large number of ______ and ________
Answer: Cations, anions
Question 3. Ionic compounds do not conduct electricity in ______ state.
Answer: Solid
Question 4. Ionic compounds conduct electricity in ________ state or in _______ solution.
Answer: Fused, aqueous
Question 5. Ionic compounds are soluble in _______ Solvents such as ________
Answer: Polar, water
Question 6. Ionic compounds are generally __________ in organic solvents.
Answer: Insoluble
Question 7. An element which forms a cation to achieve the electronic configuration of neon is _______
Answer: Sodium
Question 8. In ______ bonds, the particles are held together by electrostatic force of attraction.
Answer: Ionic
Question 9. An atom gains _______ by either accepting or losing electron(s).
Answer: Stability
Question 10. An ionic bond is formed between a _______ and a _______element.
Answer: Metallic,non-metallic
Question 11. Two elements form ionic bond with each other when the difference in electronegativity between the elements is _______
Answer: High
Question 12. An ionic compound is formed when a stable three-dimensional _______ is formed.
Answer: Crystal
Question 13. Electrovalency of Cu in cupric salts is _______
Answer: 2
Question 14. Greater the magnitude of the _______ energy of an ionic compound, the greater will be the ________ of its crystal.
Answer: Lattice, stability
Question 15. In ionic compounds, the ionisation potential of the element forming cation should be ________
Answer: Low
Question 16. In ionic compounds, the electronegativity of the elementforming anion should be _______
Answer: High
Question 17. In CaO, the charge of calcium ion is _______
Answer: 2+
Question 18. In LiH, the cation is _______ and the anion is ________
Answer: Li+, H–
Question 19. _______ bond is not considered as a real bond.
Answer: Ionic
Question 20. In 1894, Scientist _______ discovered existence of Argon gas.
Answer: Lord Raley
Question 21. Except He, all the inert gases contain ________ electrons in their valence shell.
Answer: 8
Question 22. In _______ compound bond means the electrostatic force of attraction.
Answer: Ionic
Question 23. Ionic bonds are formed between _______ and _______ elements.
Answer: Metalic,non-metallic
Ionic and Covalent Bonds Topic A Electronic Concept of Valency, Ionic Bonding, and Properties of Ionic Compounds State Whether True Or False
Question 1. Li, Be and H obeys the octet rule.
Answer: False
Question 2. Sodium chloride All the inert gas elements are chemically inert.
Answer: False
Question 3. Duplet rule is only applicable to H, Li and Be.
Answer: True
Question 4. In ionic compounds, there is no existence of independent molecules.
Answer: True
Question 5. In electrovalency, atoms complete their octet or duplet by sharing electron pairs.
Answer: False
Question 6. Ionic compounds undergo very fast reactions in solution.
Answer: True
Question 7. Crystal lattice is found in ionic compounds.
Answer: True
Question 8. Molecular mass can be calculated for ionic compounds.
Answer: False
Question 9. BN (boron nitride) is an ionic compound.
Answer: False
Question 10. Ionic bonds are real bonds as they can form crystal lattice.
Answer: False
Question 11. An example of a compound with incomplete octet is BF3.
Answer: True
Question 12. Ionic compounds are hard as the intermolecular spaces between the constituent particles are very small.
Answer: True
Question 13. Formation of ionic bond is favoured by high electron gain enthalpy of the atom that forms the anion.
Answer: True
Question 14. Ionic compounds are good conductors of electricity in solid state as the crystal lattice of ionic compounds contain free electrons.
Answer: False
Question 15. Ionic bonds are directional and hence they can show isomerism.
Answer: False
Question 16. Distilled water can conduct electricity.
Answer: False
Question 17. Individual molecules of ionic compounds do not exist.
Answer: True
Question 18. Isomerism isnotobserved in ioniccompounds.
Answer: True
Question 19. Na and Cl atoms are combined to each other by ionic valency.
Answer: True
Ionic and Covalent Bonds Topic B Covalent Bonding And Properties Of Covalent Compounds Synopsis
Covalency: In order to achieve the stable electronic configuration of the nearest noble gas, equal number of electron(s) from the outermost shells of two atoms form one or more electron pairs which are evenly shared between the two atoms. The capacity of the elements for this type of chemical combination is called covalency. The bond formed between the atoms due to covalency is called a covalent bond and the compound formed in this way is called a covalent compound.
Types of covalent bonds: Covalent bonds of three types. The atoms involved in the formation of covalent bonds may share 1, 2, or 3 electron pairs equally with each other to form a single bond, double bond, and triple bond respectively.
Characteristics of covalent compounds: Covalent compounds exist as discrete molecules. These compounds may be solid, liquid or gas and have low melting and boiling points. They usually do not conduct electricity. Covalent compounds are generally soluble in non-polar solvents and the rate of the reactions involving covalent molecules are very slow.
Lewis-dot diagram is a simple representation of a covalent molecule. Here, each electron is represented by a dot, and each bond is represented by a pair of dots in between the two atoms involved in bond formation. In the Lewis-dot diagram only the bonded electron pairs are shown.
H2, N2, O2, Cl2 etc., are examples of covalent element while NH3, CO2, CH4, HF etc., are examples of covalent compounds. Single bond is present in the molecules of H2, F2, HF, HCI, H2O, NH3, CH4, etc. Molecules like CO2, C2H4, O2, etc., contain double bond while triple bond is present in areN2, C2, H2, etc.
The Lewis-dot diagram of O2 molecule does not agree with the experimental observations regarding the structure of O2. Hence, O2 is not represented by Lewis-dot structure. In fact no such Lewis-dot structure of O2 is possible which can describe the experimental observations.
Ionic and Covalent Bonds Topic B Covalent Bonding And Properties Of Covalent Compounds Short And Long Answer Type Questions
Question 1. What is covalency?
Answer:
Covalency:
In order to achieve the electronic configuration of the nearest noble gas, equal number of electron(s) from the outermost shells of two atoms form one or more electron pairs which are evenly shared by the two atoms. The capacity of the elements for this type of chemical combination is called covalency.
Question 2. What are covalent bonds and covalent compounds?
Answer:
Covalent bonds and covalent compounds
The bond formed between the atoms by the mutual sharing of electron pairs is called covalent bond and the compound containing covalent bonds is called a covalent compound.
Question 3. Classify covalent molecules.
Answer:
Covalent molecules are of two types. These are:
1. Covalent elementary molecules: The atoms of the same element are covalently bonded with each other to form covalent elementary molecules. H2, N2, O2 F2, etc., are examples of this type.
2. Covalent compound molecule: The atoms of different elements are covalently bonded with each other to form covalent compound molecules. NH3, CO2, HCl, and CH4 are examples of this type.
Applications of Ionic and Covalent Bonds in Chemistry
Question 4. How is a covalency covalent molecule?
Answer: During the formation of a covalent molecule, the number of electron pairs formed by an atom of an element is its covalency. For example, in methane (CH4) C-atom forms four electron pairs with 4 hydrogen atoms. Hence, covalency of carbon in methane is 4.
Question 5. Glucose is a solid but methane is a gas though both are covalent compounds. Explain.
Answer:
Glucose is a solid but methane is a gas though both are covalent compounds
The force of attraction between the molecules of a covalent compound is very weak and the attractive force increases with an increase in molecular mass.
The molecular mass of glucose is much higher than that of methane and hence the force of attraction between glucose molecules is stronger than that between methane molecules. Hence, glucose is solid at room temperature but methane Is a gas.
Question 6. Explain why naphthalene is insoluble in water but readily dissolves in benzene.
Answer: Covalent molecules are generally insoluble in polar solvents and soluble in non-polar solvents. Water is a polar solvent while benzene is a nonpolar solvent. Thus, naphthalene being a covalent compound dissolves in benzene but is insoluble in water.
Question 7. An aqueous solution of sodium chloride conducts electricity, but aqueous solution of sugar or glucose does not conduct electricity. Explain why.
Answer:
An aqueous solution of sodium chloride conducts electricity, but aqueous solution of sugar or glucose does not conduct electricity.
Sodium chloride (NaCI) being an ionic compound dissociates in aqueous solution to form Na+ and Cl– ions. These ions are responsible for conducting electricity and hence NaCI is a good conductor of electricity in aqueous solution. On the other hand, sugar or glucose being covalent compound does not dissociate in solution and hence they do not conduct electricity.
Question 8. Though HCI is a covalent compound, its aqueous solution conducts electricity. Why?
Answer:
Though HCI is a covalent compound, its aqueous solution conducts electricity.
The electronegativity of chlorine is greater than that of hydrogen. As a result, the electron pair shared between H and Cl-atom in HCI molecule shifts more towards Cl-atom. Due to this, a partial positive charge develops on H-atom and a partial negative charge develops on Chatom.
Water is also a polar molecule in which H-atom is partially positively charged and O-atom is partially negatively charged. Due to force of attraction between the opposite charges of HCI and water molecules, HCI ionises to form H3O+ and Cl– ions. As a result, of the formation of these ions in solution, HCI conducts electricity.
Question 9. Why are the melting and boiling point of covalent compounds generally low?
Answer: The intermolecular force acting between the molecules of covalent compounds is very weak. Hence, less energy is required to separate the molecules. So, covalent compounds generally have low melting and boiling point.
Question 10. The reactions involving covalent molecules are slow. Explain with reason.
Answer:
The reactions involving covalent molecules are slow.
In covalent molecules, the atoms are bonded by strong covalent bonds. The cleavage of these bonds requires sufficient energy, time and sometimes catalysts. That is why, reactions involving covalent molecules take place slowly. For example— fermentation of glucose to ethanol takes almost 3 days to complete.
Common Misconceptions About Ionic and Covalent Bonds
Question 11. Cl2 molecules are formed but Ne2 molecules do not exist. Explain why.
Answer:
Cl2 molecules are formed but Ne2 molecules do not exist.
Cl-atom has 7 electrons in its outermost shell. Two chlorine atoms contribute one electron each to form a commonly shared pair and in this way, both of them complete their octets.
The sharing of the electron pair results in the formation of Cl2 molecule. On the other hand, Ne-atoms already have filled octet and hence do not show any tendency to combine with each other to form Ne2 molecule.
Question 12. What is polar covalent bond?
Answer:
Polar covalent bond?:
When a covalent bond is formed between two atoms of different elements, due to the difference in electronegativity between the atoms the shared electron pair is attracted more towards the atom with greater electronegativity.
As a result the more electronegative atom becomes partially negatively charged. On the other hand, the less electronegative element develops a partial positive charge. This charge difference between the atoms causes polarity in the covalent bond. This type of bond is called polar covalent bond.
Question 13. Discuss about the electrical conductivity of covalent compound.
Answer:
The electrical conductivity of covalent compound:
Covalent compounds do not possess cations or anions and so cannot usually conduct electricity in the fused or dissolved state. However, some covalent compounds when dissolved in a polar solvent form ions by reacting with the solvent molecules and conducting electricity.
For example, hydrogen chloride dissolves in water and forms hydronium ions and chloride ions by reacting with water molecule. As a consequence aqueous solution of hydrogen chloride can conduct electricity.
\(\mathrm{HCl}+\mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{H}_3 \mathrm{O}^{+}+\mathrm{Cl}^{-}\)
Question 14. Mention which of the following compounds conduct electricity and which can not—Cl2, Al2O3, an aqueous solution of HO, NaBr.
Answer: Al2O3, aqueous solution of HCI and NaBr can conduct electricity and Cl2 can not conduct electricity.
Question 15. Classify the following compound as ionic and covalent compound—CCI4, Na2SO4, CaCI2, CaO, CHCI3, C2H2, NaH, LiH, MgO, NaBry NaCI, Cl2, O2, H2O, KCI, N2, CO2, Na2O, NH3, Mg(NO3)2, K2S, C2H6, HCI, NaF, MgCI2, CH4.
Answer:
Ionic compound: Na2SO4, CaCl2, CaO, NaH, LiH, MgO, NaBr, NaCI, KCI, Na2O, Mg(NO3)2, K2S, NaF, MgCI2.
Covalent compound: CCI4, CHCI3, C2H2, Cl2, O2, H2O, N2, CO2, NH3, C2H6, HCl, CH4.
Question 16. Compare naphthalene and sodium chloride by the following properties—boiling point and solubility in water.
Answer:
Comparison between naphthalene and sodium chloride are:
Property | Naphthalene | Sodium chloride |
Boiling point | Since naphthalene is a covalent compound its boiling point is comparatively low(80.2°C). | Being an ionic compound sodium chloride has a comparatively higher boiling point (801°C). |
Solubility in water | Naphthalene is insoluble in water. | Sodium chloride is soluble in water. |
Question 17. Differentiate between ionic and covalent compounds on the basis of the following properties:
1. Hardness and brittleness and
2. Melting and boiling point.
Answer:
The differences are listed below:
Property | Ionic compound | Covalent compound |
1. Hardness and brittleness | The crystals of ionic compounds are hard and brittle in nature. | Most of the solid covalent compounds are very soft. However, some covalent compounds are able to form giant crystal lattices having a high degree of hardness. |
2. Melting and boiling point | Ionic compounds generally have high melting and boiling point. | Except for some solid covalent compounds ( SiO2 etc.), the melting and boiling point of most covalent compounds are low. |
Question 18. Differentiate between ionic and covalent compounds on the basis of the following properties:
1. Electric conductance and
2. Solubility.
Answer:
The differences are listed below:
Property | Ionic compound | Covalent compound |
1. Electrical conductance | Ionic compounds are non-conductors of electricity in solid state but in aqueous solution or in molten state they conduct electricity. | Pure covalent compounds are usually non-conductors of electricity. (Exception— aqueous solution of HCI conducts electricity). |
2. Solubility | Ionic compounds are generally soluble in polar solvents but insoluble in non-polar solvents. | Covalent compounds are generally soluble in non-polar solvents but insoluble in polar solvents. However, covalent compounds such as HCl, sucrose, glucose, ethanol are soluble in water. |
Question 19. Differentiate between ionic and covalent compounds on the basis of the following properties:
1. Nature of bond and
2. Electrolytic nature.
Answer:
The differences are listed below:
Property | Ionic compound | Covalent compound |
1. Nature of bond | Ionic compounds are formed by the electrostatic force of attraction acting between two oppositely charged ions. There is no existence of discrete molecules. | Covalent compounds are formed by sharing of equal number of electron pairs between the two atoms. Covalent compounds form discrete molecules. |
2. Electrolytic nature | Almost all ionic compounds are electrolytes in a molten state or when dissolved in a suitable solvent. | Most covalent compounds are nonelectrolytes. However, some polar covalent compounds (e.g, HCI) ionise in polar solvents and hence act as electrolytes. |
Question 20. State three important differences between ionic and covalent bond.
Answer:
The three major differences between ionic and covalent bonds are discussed below:
Characteristic | Ionic bond | Covalent bond |
1. Process of bond formation | An ionic bond is formed by transfer of electron(s) from the atom of an electropositive element to the atom of an electronegative element. | The atoms involved in covalent bond formation share equal number of electrons to form electron pair(s) and both of them use these electron pair(s) equally to form a covalent bond. |
2. Difference in electronegativity | The difference in electronegativity of the participating atoms is very high. | The participating atoms have comparable electronegativity. |
3. Nature of bond | It is actually an electrostatic force of attraction. | The force of attraction arises due to sharing of electron pairs is known as a covalent bond. |
Question 21. Explain with an example how the covalent bond is formed according to Lewis’s concept.
Answer:
G.N. Lewis (1916) proposed an electronic model, according to which, when both the atoms taking part in a chemical combination are short of electrons than the stable electronic configuration of the nearest noble gas, they can share their electrons in order to complete their octets (duplet in the case of H) to form a covalent bond.
During formation of a covalent bond, the two combining atoms contribute equal number of electrons for sharing. The shared electrons become a common property of both atoms and are responsible for holding the atoms together. Since such a combination of atoms does not involve the transfer of electrons form one atom to another, the atoms are electrically neutral.
Example: Of the two F-atoms (electronic configuration 2, 7), one electron from each F atoms are shared to form an electron pair. This electron pair is then used by both atom to attain the stable configuration like Ne-atom. (electronic configuration: 2, 8). As a consequence, F2 molecule is formed.
Question 22. Describe the formation of hydrogen molecule using Lewis-dot structure.
Answer:
Formation of hydrogen molecule using Lewis-dot structure
Hydrogen molecule is diatomic. Two hydrogen atoms combine with each other by single bond to form H2 molecule. Hydrogen atom contains a single electron in its K orbit. During the formation of H2 molecule, two hydrogen atoms share 1 electron each to form an electron pair, and this electron pair equally.
As a result, both the atoms attain the electronic configuration of the nearest noble gas He. Due to sharing of an electron pair, a single bond is formed between two H -atoms to form an H2 molecule.
Question 23. Justify the Lewis-dot structure of oxygen.
Answer:
The Lewis-dot structure of oxygen
Two O-atoms combine with each other by forming covalent double bond (O=O) in which both the atoms attain the stable electronic configuration of Ne. But the Lewis-dot structure of oxygen molecule fails, to explain all the experimental observations regarding the structure of O2 molecule.
Actually, no such Lewisdot structure of O2 molecule can describe all the properties of oxygen.
Question 24. Describe the formation of F2 molecule with the help of Lewis-dot diagram. Or, Describe the formation of homonuclear diatomic molecule.
Answer:
The formation of F2 molecule with the help of Lewis-dot diagram
Two F-atoms combine chemically by forming a single covalent bond to form an F2 molecule. An F -atom contains 2 electrons in its K orbit and in its L orbit. During the formation of F2 molecule, each F-atom shares one electron from its valence shell equally with the other to form an electron pair. As a result, both the atoms attain the stable electronic configuration of the nearest noble gas Ne. This results in the formation of stable F2 molecule.
Question 25. Explain how an HF molecule is formed with the help of Lewis-dot diagram.
Answer: HF molecule is formed by the chemical combination of an H-atom and an F-atom. H-atom has 1 electron in its valence shell. On the other hand, F-atom has 7 electrons in its valence shell.
During chemical combination, an H-atom and an F-atom share one electron each from their valence shell to form an electron pair which is equally shared between them. As a result, both the atoms attain the stable electronic configuration of their nearest noble gases. This results in the formation of HF molecule.
Question 26. Explain how an HCI molecule is formed with the help of Lewis-dot diagram. Or, Describe the formation of a heteronuclear diatomic molecule.
Answer: An HCI molecule is formed by the chemical combination of an H-atom and a Cl-atom. H-atom has 1 electron in its valence shell. On the other hand, Cl-atom has 7 electrons in its valence shell.
During chemical combination, an H-atom and a Cl-atom share one electron each from their valence shell to form an electron pair which is equally shared between them. As a result, both the atoms attain the stable electronic configuration of their nearest noble gases. This results in the formation of HCI molecule.
Question 27. Describe the formation of molecule with the help of Lewis-dot diagram.
Answer:
The formation of molecule with the help of Lewis-dot diagram:
In H2O molecule, an O-atom is covalently bonded to two H-atoms. H-atom has 1 electron in its valence shell. On the other hand, O-atom has 6 electrons in its valence shell. During chemical combination, an oxygen atom shares its two valence electrons to separately pair with each electron of the two H-atoms.
As a result, O-atom attains the stable electronic configuration of Ne and both the hydrogen atoms attain the electronic configuration of He. Thus, two single bonds are formed between O-atom and two H-atoms. The other two pairs of electrons in the valence shell of oxygen atom do not take part in bond formation and remain as lone pairs of electrons.
Question 28. Describe the formation of NH3 molecule with the heip of Lewis-tlot diagram.
Answer:
The formation of NH3 molecule with the heip of Lewis-tlot diagra
In NH3 molecule, N-atom is covalently bonded with three H-atoms. H-atom has 1 electron in its valence shell. On the other hand, N-atom has 5 electrons in its valence shell. During chemical combination, a nitrogen atom shares its three valence electrons to separately pair with each electron of the three H-atoms.
As a result, N-atom attains the stable electronic configuration of Ne and all the three hydrogen atoms attain stable electronic configuration of He. Thus, three single bonds are formed between N-atom and three H-atoms. One pair of electron in the valence shell of nitrogen does not take part in bond formation and remains as lone pair of electron.
Question 29. Describe the formation of CH4 molecule with the help of Lewis-dot diagram.
Answer:
The formation of CH4 molecule with the help of Lewis-dot diagram:
In a CH4 molecule, a C-atom (2,4) is covalently bonded with four H-atoms. H-atom has 1 electron in its valence shell. On the other hand, C-atom has 4 electrons in its valence shell. During the chemical combination, a carbon atom shares its four valence electrons to separately pair with each electron of the four H-atoms.
As a result, C- atom attains the stable electronic configuration of Ne and all the four hydrogen atoms attain the electronic configuration of He and become stable. Thus, four single bonds are formed between C- atom and four H-atoms. This results in the formation of CH4 molecule.
Question 30. Describe how a CO2 molecule is formed with the help of Lewis-dot diagram.
Wbbse Class 10 Properties Of Covalent Compounds
Answer: During the formation of CO2 molecule, two electrons out of the 4 valence electrons of C-atom are shared with 2 valence electrons of an oxygen atom.
As a result, a double bond is formed between C-atom and its O-atom. C-atoms uses its remaining two valence electrons to form a double bond with another O-atom similarly. Thus, in a CO2 molecule the C-atom forms two double bonds with two oxygen atoms.
Question 31. Describe the formation of a C2H4 molecule with the help of Lewis-dot diagram.
C2h4 Covalent Bond Diagram
Answer:
The formation of a C2H4 molecule with the help of Lewis-dot diagram
Ethylene molecule is formed by the combination of two C-atoms with four H-atoms. Each of the two C-atoms share two valence electron pairs with each other to form a double bond (C — C). Each of the C-atoms uses its two remaining valence electrons to form two single bonds with two hydrogen atoms. Thus, the molecule contains four C—H bonds apartfrom a C = C bond.
Question 32. Describe the formation of a N2 molecule with the help of Lewis-dot diagram.
Answer:
The formation of a N2 molecule with the help of Lewis-dot diagram
During the formation of N2 molecule by the combination of two N-atoms (2,5), each N-atom shares its three valence electrons with three valence electrons of the other N-atom. Thus, three electron pairs are formed, which are equally shared by both N -atoms. Due to sharing of three electron pairs, a triple bond is formed between two N-atoms, and N2 molecule is formed.
C2h4 Covalent Bond Diagram
Question 33. Describe how a C2H2 molecule is formed with the help of Lewis-dot diagram.
Answer: An acetylene molecule is formed by the combination of two C-atoms with two H-atoms. Each of the two C-atoms share three electron pairs with each other to form a triple covalent bond (C = C). Each of the C-atoms uses its remaining valence electron to form single bond with a hydrogen atom, Thus, C2H2 molecule contains two C—H bonds apart from a C=-C bond.
Question 34. Draw the Lewis dot structure of CCI4.
Answer:
Lewis dot structure of CCI4
Question 35. Through what sort of chemical bonding does chloride combines with sodium and hydrogen to form sodium chloride and hydrogen chloride- respectively? Draw corresponding electron dot structure in both cases.
Wbbse Class 10 Properties Of Covalent Compounds
Answer: Chlorine combines with sodium through ionic bonding or electrovalent bonding and with hydrogen through covalent bonding. Electron dot structure of sodium chloride Electron dot structure of hydrogen chloride:
Electron dot structure of hydrogen chloride:
Question 36. Atomic number of the elements X, Y, and Z are respectively 9, 10, and 11.
1. Which one of them will form ionic bond only and which one will form both ionic and covalent bonds? Answer bn the basis of electronic configuration only.
2. Draw the Lewis-dot diagram of the compounds formed by the combination of these elements.
Answer:
1. Electronic configuration of X is K = 2, L = 7 . The electronic configuration of Y is AT = 2, L = 8. The electronic configuration of Z is K= 2, L = 8, and M = 1.
C2h4 Covalent Bond Diagram
X has 7 electrons in its outermost orbit. So, it will form both ionic and covalent bonds. The complete octet of Vindicates that it is chemically inert. Z has only 1 electron in its outermost shell. Hence, it can form ionic bonds only.
2. Atoms of X and Z will combine with each other to form a compound ZX.
Two atoms of element X combine with each other to form X2 molecule.
Visual Representation of Ionic and Covalent Bonding
Question 37. Number of valence electrons in the atoms of the elements A, B, C, and D are respectively 1, 4, 6, and 7. Form two ionic and two covalent compounds with these elements and draw their structures.
Answer:
Element | A | B | C | D |
Number of valence electrons | 1 | 4 | 6 | 7 |
Ionic compounds formed from these elements are:
Covalent compounds formed from the these elements are:
Question 38. Atomic numbers of elements A, B and C are 3,11, and 19 respectively. Which type of compound, ionic or covalent, will be formed by the reaction of B with chlorine?
Answer:
Element | Atomic No. | Electronic configuration | |||
A | 3 | 2 | 1 | ||
B | 11 | 2 | 8 | 1 | |
C | 19 | 2 | 8 | 8 | 1 |
The atom of element B contains 1 electron in its valence shell which may be donated to attain the stable electronic configuration. On the other hand Cl (electronic configuration: 2, 8, 7) atom has the tendency to accept electron to attain the stable electronic configuration.
Hence atom of B will lose 1 electron to form the B⊕ ion and ClΘ ion. These two ions will hold together, to form BCI, by a strong electrostatic force of attraction. Hence ionic compound will be formed by the reaction of B with chlorine.
Question 39. Atomic number of the element X is 7. If two atom of X combines to form molecule, then which type of bond-ionic or covalent will be formed? Draw the electron dot structure of the molecule.
Answer: Electronic configuration of X is 2, 5. Each of the two combining atoms of X will contribute 3 electrons form their valence shell to form 3 common shared pair of electron and in this way both of them complete their octets. Hence covalent triple bond will be formed during the formation of X2 molecule.
Question 40. Assume symbols of two elements are A and B and their atomic numbers are 7 and 20 respectively. If two atom of A combine to form a molecule then which type of bonding occurs during bond formation. Draw the electron dot structure of the molecule.
Answer:
1. During the formation of molecule of A by the combination of two atoms of it will combine through covalent bonding.
2. Electronic configuration of A is 2, 5.
Now electron dot structure of the molecule A2.
Ionic and Covalent Bonds Topic B Covalent Bonding And Properties Of Covalent Compounds Very Short Answer Type Questions Choose The Correct Answer
Question 1. With respect to covalent compounds, the melting points of ionic compounds are generally
- Lower
- Higher
- Equal
- Lower or higher
Answer: 2. Higher
Question 2. Which of the following is insoluble in water?
- MgCI2
- Na2SO4
- CHCI3
- HCL
Answer: 3. CHCI3
Wbbse Class 10 Properties Of Covalent Compounds
Question 3. A covalent compound used in our daily life is
- Washing soda
- Alum
- Water
- Chalk
Answer: 3. Water
Question 4. Both ionic and covalent bonds can not be formed by
- H
- O
- Na
- Cl
Answer: 3. Na
Question 5. Which of the following compounds form both ionic and covalent bonds?
- NH3
- CCI4
- CO2
- CaCO3
Answer: 4. CaCO3
Physical Science Class 10 West Bengal Board
Question 6. Which of the following, though covalent, but possesses high melting point?
- C2H6
- SiO2
- C4H10
- CO2
Answer: 2. SiO2
Question 7. The concept of covalent bonding was given by
- Lewis
- Arrhenius
- Kelvin
- Avogadro
Answer: 1. Lewis
Question 8. The Lewis structure does not justify the experimental result for
- N2
- NH3
- CH4
- O2
Answer: 4. O2
Question 9. A double bond is present in
- H2O
- NH3
- CO2
- CH4
Answer: 3. CO2
Physical Science Class 10 West Bengal Board
Question 10. A triple bond is present in’
- H2
- O2
- N2
- F2
Answer: 3. N2
Question 11. Elements forming covalent bonds are placed in periodic table at the
- Extreme left
- Extreme right
- Middle of the table
- The bottom
Answer: 2. Extreme right
Question 12. Maximum number of covalent bonds that can be formed between two atoms is
- 1
- 2
- 3
- 4
Answer: 3. 3
Question 13. In which of the following compounds, the central atom has an expanded octet?
- CH4
- PCI5
- NH3
- NCl3
Answer: 2. PCI5
Question 14. In which of the following compounds, the central atom has an incomplete octet?
- HCN
- BF3
- CO2
- H2O
Answer: 2. BF3
Physical Science Class 10 West Bengal Board
Question 15. Covalent bond is not formed between
- C&CI
- B&F
- Cl & Cl
- Na & F
Answer: 4. Na & F
Question 16. A triple bond is absent in
- C2H2
- N2
- HCN
- C2H4
Answer: 4. C2H4
Question 17. The nature of the bonds in HCI(g) .
- Covalent
- Ionic
- Coordinate
- Ionic and covalent
Answer: 1. Covalent
Wbbse Class 10 Properties Of Covalent Compounds
Question 18. In which of the following compounds ionic, covalent and coordinate—all the three types of bond are present?
- KCI
- H2O
- NH4CI
- NaCN
Answer: 3. NH4CI
Question 19. Which of the following combines with hydrogen to form covalent compounds?
- Ca
- Na
- C
- Li
Answer: 3. C
Question 20. Which of the following is a covalent compound?
- CaO
- MgO
- NaCI
- CH4
Answer: 4. CH4
Question 21. Which of the following compound central atom contains lone pair of electron?
- CH4
- NH3
- C2H2
- C2H4
Answer: 2. NH3
Physical Science Class 10 West Bengal Board
Question 22. A compound with covalent triple bond is
- H2O
- CO2
- C2H2
- CH4
Answer: 3. C2H2
Question 23. Compound containing covalent double bond is
- OF2
- N2
- C2H4
- C2H2
Answer: 3. C2H4
Wbbse Class 10 Properties Of Covalent Compounds
Question 24. Which one of the following does not conduct electricity in molten state or in solution?
- NaCI
- NaF
- CCI4
- KCI
Answer: 3. CCI4
Question 25. True bond can be found in
- Ionic bond
- Covalent bond
- Nuclear bond
- None of these
Answer: 2. Covalent bond
Question 26. Number of covalent bonds in nitrogen molecule is
- 1
- 2
- 3
- 4
Answer: 3. 3
Physical Science Class 10 West Bengal Board
Question 27. In which of the following compound covalent bonds are present?
- Hydrogen chloride
- Sodium chloride
- Lithium hydroxide
- Calcium oxide
Answer: 1. Hydrogen chloride
Ionic and Covalent Bonds Topic B Covalent Bonding And Properties Of Covalent Compounds Answer In Brief
Question 1. Name a non-polar solvent.
Answer: Benzene is a non-polar solvent.
Question 2. Between water and benzene, which one dissolves kerosene?
Answer: Kerosene, a covalent organic substance, dissolves in a non-polar solvent like benzene.
Question 3. Name a crystalline substance that contains covalent bonds.
Answer: Diamond is a crystalline solid in which C-C covalent bonds are present.
Question 4. Name a covalent solid whose hardness is more than any ionic compound.
Answer: Diamond, a covalent compound, is the hardest substance. Its hardness is more than any ionic compound.
Question 5. How many lone pairs of electrons are present in nitrogen molecules?
Answer: Nitrogen molecule contains two lone pairs of electrons (N = N).
Wbbse Class 10 Properties Of Covalent Compounds
Question 6. Define crystal lattice.
Answer:
Crystal lattice
A crystal lattice is defined as a regular three-dimensional network of constituent particles (atoms, molecules, or ions) of the crystal.
Physical Science Class 10 West Bengal Board
Question 7. The atomic number of an element is 6. What type of bond will it form with the element having atomic number 17?
Answer: Both elements are non-metals. So, they will form covalent bonds.
Physical Science Class 10 West Bengal Board
Question 8. Name an electronegative element that forms both ionic and covalent compounds.
Answer: Chlorine forms both ionic and covalent compounds.
Question 9. What happens when crystals of sugar are heated?
Answer: When crystals of sugar are heated, it releases molecules of water and black particles of carbon are left behind as residue.
Word Problems Involving Ionic and Covalent Bonds
Question 10. Name a non-volatile covalent compound.
Answer: Sugar or cane sugar (C12H22O11) is a nonvolatile covalent compound.
Question 11. Give example of a solid and a liquid covalent compound.
Answer: A solid covalent compound is a glucose (C6H12O6) and a liquid covalent compound is water (H2O).
Question 12. Between water and ethanol, which one is more volatile?
Answer: Ethanol is more volatile than water.
Question 13. Is it possible to differentiate between solid naphthalene and solid common salt on the basis of their electrical conductivity?
Answer: In solid state, both naphthalene and common salt are bad conductors of electricity. Hence, it is not possible to differentiate between them on the basis of their electrical conductivity.
Physical Science Class 10 West Bengal Board
Question 14. How many covalent bonds can be formed between two atoms?
Answer: Two atoms can form a maximum of 3 covalent bonds between them.
Question 15. Show the structure of C2H2 by dash formula.
Answer: H—C=C—H.
Physical Science Class 10 West Bengal Board
Question 16. Give an example of a single bonded covalent molecule which is liquid at normal temperature.
Answer: Water is a single bonded covalent molecule which is liquid at normal temperature.
Question 17. Name a gaseous hydrocarbon that contains only single bonds.
Answer: Methane (CH4) is a gaseous hydrocarbon that contains only single bonds.
Wbbse Class 10 Properties Of Covalent Compounds
Question 18. Name a gaseous hydrocarbon that contains double bond.
Answer: Ethylene (C2H4) is a gaseous hydrocarbon that contains a double bond.
Question 19. Give an example of a molecule which contains an atom having a lone pair of electrons.
Answer: In ammonia (NH3) molecule, the nitrogen atom contains a lone pair of electrons.
Question 20. The electronic configuration of N-atom is 2(K), 5(L). How many electrons in the valence shell of nitrogen do not take part in the formation of N2 molecule?
Answer: 2 electrons from each N-atom do not take part in the formation of N2 molecule.
Question 21. Name a gaseous covalent compound which ionises in aqueous solution and conducts electricity.
Answer: Hydrogen chloride (HCI) is a gaseous covalent compound which ionises in an aqueous solution and conducts electricity.
Question 22. What is Lewis-dot diagram?
Answer:
Lewis-dot diagram
Lewis-dot diagram is a simple representation of a covalent molecule. Here, each electron is represented by a dot, and each bond is represented by a pair of dots in between two atoms involved in bond formation.
Physical Science Class 10 West Bengal Board
Question 23. What is the linear formula of covalent compounds?
Answer: Linear formula of a covalent compound is a simple representation in which each covalent bond is represented by a line or dash between the atoms involved in bond formation.
Question 24. How many types of covalent bonding are there?
Answer: There are three types of covalent bond single bond, double bond, and triple bond.
Question 25. Isomerism can be found in which type of compound?
Answer: Covalent compound.
Wbbse Class 10 Properties Of Covalent Compounds
Question 26. Give example of a solid covalent which is good conductor of electricity.
Answer: Graphite.
Question 27. Give example of a single bonded covalent compound which is liquid at room temperature.
Answer: Water.
Question 28. Give example of two covalent compounds whose boiling and melting points are very high.
Answer: Boron carbide ( B4C) and Silica ( SiO2).
Question 29. Which one between ionic or covalent compounds are generally electrolytes?
Answer: Ionic compounds are generally electrolytes.
Question 30. Which type of chemical bond is present in hydrogen chloride molecule?
Answre: Covalent bonds are present in pure hydrogen chloride molecule.
Question 31. Draw the Lewis dot structure of F2 molecule.
Answer:
Question 32. Which type of bond is present in HF?
Answer: Covalent bonding is present in HF.
Question 33. By which type of bonding do carbon and hydrogen atoms combine to form methane?
Answer: Covalent single bond.
Ionic and Covalent Bonds Topic B Covalent Bonding And Properties Of Covalent Compounds Fill In The Blanks
Question 1. An example of a solid covalent crystalline compound is ______
Answer: Sugar
Question 2. The total number of valence electrons in the atoms of the molecule of HCN is _______
Answer: 10
Question 3. Ethanol is _______ in water.
Answer: Soluble
Question 4. Chloroform and water are _______ each other.
Answer: Immiscible
Question 5. An aqueous solution of glucose is a _______ of electricity.
Answer: Non-conductor
Wbbse Class 10 Properties Of Covalent Compounds
Question 6. _______is a covalent substance that conducts electricity in a solid state.
Answer: Graphite
Question 7. Only _______ electrons are shown in the Lewis-dot diagram.
Answer: Bonded
Question 8. ______ is an example of a covalent compound which is widely used as a solvent.
Answer: Water
Question 9. Sugar does not ______ in aqueous solution.
Answer: Ionise
Question 10. Covalent bonds are formed due to the formation of _______
Answer: Electron-pairs
Question 11. The covalent bond in HCI is _______ in nature.
Answer: Polar
Question 12. The number of lone pairs of electrons in O atom of H2O molecule is _______
Answer: 2
Question 13. _________ is a covalent compound in which all the 4 bonds are identical.
Answer: Methane
Question 14. The number of bond pairs of electrons in CO2 is _______
Answer: 4
Wbbse Class 10 Properties Of Covalent Compounds
Question 15. Among CH4, C2H4 and C2H2, triple bond is present in _______
Answer: C2H2
Question 16. Covalent bond has a definite _______
Answer: Direction
Question 17. In NH3 molecule, N-atom has ______ lone pair of electrons.
Answer: 1
Question 18. The structure of covalent compounds are represented by ______ diagram.
Answer: Lewis-dot
Question 19. The number of single bonds present in C2H4 is a _______
Answer: 4
Question 20. Number of covalent bonds present i nitrogen molecule is _____
Answer: Three
Ionic and Covalent Bonds Topic B Covalent Bonding And Properties Of Covalent Compounds State Whether True Or False
Question 1. Lewis-dot diagram cannot explain’ the experimental observation regarding the structure of O2.
Answer: True
Question 2. Boiling and melting point of covalent compounds are high due to strong force of attraction between the covalent molecules.
Answer: False
Question 3. van der Waal’s force of attraction between two covalent molecules increases as the molecular mass increases.
Answer: True
Question 4. A coordinate bond can be found in H3O+ ion.
Answer: True
Question 5. Covalent compounds can exist as discrete molecules.
Answer: True
Question 6. Covalent compounds can be soft solid at normal temperature.
Answer: True
Question 7. Some transition metal elements can form four bonds between two atoms.
Answer: True
Question 8. Formula mass and molecular mass are not the same for covalent compounds.
Answer: False
Question 9. NaH is a covalent compound.
Answer: False
Question 10. Aqueous solution glucose can conduct electricity.
Answer: False
Question 11. Carbon tetrachloride is a polar solvent.
Answer: False
Question 12. Maximum two covalent bonds can be formed between two atoms.
Answer: False
Question 13. There are 5 covalent bonds present in ethyne molecule.
Answer: True
Ionic and Covalent Bonds Miscellaneous Type Questions Match The Columns
Question 1.
Column A | Column B |
CaCO3 | 1. Ionic and soluble in water |
NaCI | 2. Contains coordinate bond |
NH4+ | 3. Covalent but conducts electricity in solution |
HCI | 4. Ionic but insoluble in water |
Answer:
CaCO3: 4. Ionic but insoluble in water:
NaCI: 1. Ionic and soluble in water
NH4+: 2. Contains coordinate bond
HCI: 3. Covalent but conducts electricity in solution
Question 2.
Column A | Column B |
The Duplet rule is applicable for | 1. Na |
Electrovalency | 2. Be |
Both ionic and covalent bonds are not formed by | 3. PCI5 |
Expanded octet | 4. Electrostatic force of attraction |
Answer:
The Duplet rule is applicable for: 2. Be
Electrovalency: 4. Electrostatic force of attraction
Both ionic and covalent bonds are not formed by: 1. Na
Expanded octet: 3. PCI5
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