WBBSE Solutions for Class 9 Physical Science Chapter 4 Matter Nuclear Force

Chapter 4 Matter Nuclear Force Synopsis

Isotopes: Atoms of same elements with the same atomic number but different mass number are called isotopes,

Example: \({ }_1 H^1\) (protium), \({ }_1 H^2\) (deuterium), \({ }_1 H^3\) (tritium).

Properties Of Isotopes: The chemical properties of the isotopes of an element are identical, but the physical properties which depend on the atomic masses are different.

Uses Of Isotopes:

1. The age of the earth, antiques, fossils, old plants can be. determined with the help of radioactive \({ }_6 C^14\) isotope.
2. Radioactive isotopes like \({ }_15 P^32\), \({ }_27 Co^60\), \({ }_53 I^131\) etc., are used in the treatment of cancer, goitre, tumors.
3. Various isotopes are used in the agricultural field and also used for determining the mechanism of various chemical reactions.

Isobars: Atoms which have the same mass number but different atomic numbers are called isobars.

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Example: \({ }_18 Ar^40\) and \({ }_20 Ca^40\) (tritium).

Properties Of Isobars: Isobars have different physical and chemical properties.

Isotones: Atoms which have the same number of neutrons but different number of protons are called isotones.

Example: \({ }_1 H^3\), \({ }_2 He^4\) and \({ }_6 C^14\), \({ }_7 N^15\), \({ }_8 O^16\) etc.

Properties Of Isotones: Physical and chemical properties of isotones are different.

Nuclear Force: It is a strong attractive force acting between the nucleons present in an atomic nucleus and it holds the nucleons together. It is created by the continuous exchange of meson particles between one proton and one neutron.

Rules For Distribution Of Electrons In Different Orbits:

1. Maximum number of electrons in a stationary orbit =2n², where n is the principal quantum number.
2. Maximum number of electrons in the outermost shell of an atom is 8.
3. Electrons do not enter to a higher orbit keeping a lower orbit completely empty.

Electronic Configurations Of Some Elements

Chapter 4 Matter Nuclear Force Short And Long Answer Type Questions

Question 1. Define isotope with example.

Answer:

Isotope:-

Isotopes (Greek: iso = same, topos = place) are defined as the atoms of the same element having the same atomic number but different mass number due to the presence of different number of neutrons in the nucleus.

Examples:

There are 3 isotopes of hydrogen – protium or ordinary hydrogen (\({ }_1^1 \mathrm{H}\)), deuterium (\({ }_1^2 \mathrm{H}\)) and tritium (\({ }_1^3 \mathrm{H}\)).

There are 3 isotopes of carbon- \({ }_6^{12} \mathrm{C}\), \({ }_6^{13} \mathrm{C}\) and \({ }_6^{14} \mathrm{C}\).

Question 2. Define isobars with example.

Answer:

Isobars:-

Isobars are atoms of different elements having the same mass number but different atomic numbers.

Example: \({ }_{20}^{40} \mathrm{Ca} \text { and }{ }_{18}^{40} \mathrm{Ar}\) are isobars. They have the same mass number (40) but their atomic numbers are different.

Question 3. Define isotones with example.

Answer:

Isotones:-

Isotones are the atoms of different elements having the same number of neutrons but different atomic numbers and mass numbers.

Example: \({ }_6^{14} \mathrm{C},{ }_7^{15} N,{ }_8^{16} \mathrm{O}\) are isotones as they have the same number of neutrons (8) but different atomic numbers and mass I numbers.

Question 4. The constituents of two nuclei are as follows

Find The Relation Between A And B.

Answer:

The atomic number of both the atoms A and B is 17.

Mass number of A = number of protons + number of neutrons = 17 + 18 = 35

Mass number of B = number of protons + number of neutrons = 17 + 20 = 37

Hence, A and B are the isotopes of a particular element.

Question 5. Why do isotopes of the same element possess identical chemical properties?

Answer:

Chemical properties of an element depend on its atomic number and the electronic configuration of the element. Isotopes of the same element may have different number of neutrons, but they possess the same number of protons and also have identical electronic configuration.

Thus, isotopes of the same element have identical chemical properties.

Question 6. Write three differences between isotopes and isobars.

Answer:

Differences Between Isotopes And Isobars Are:-

Question 7. What are the different characteristic features of isotopes?

Answer:

Characteristic Features Of Isotopes Are:-

1. The isotopes of an element have the same number of electrons and identical electronic configuration. Hence, they possess identical chemical properties.
2. The atomic masses of isotopes are different. Hence, the physical properties related to mass such as density, melting point, boiling point, rate of diffusion etc., are different for different isotopes.
3. Due to different nuclear structures, different isotopes may have different nuclear properties. For example, \({ }_6^{12} C\) isotope of carbon is non-radioactive while \({ }_6^{14} C\) isotope of carbon is radioactive.

Question 8. What are the different characteristic features of isobars?

Answer:

Different Characteristic Features Of Isobars Are:-

1. Isobars are atoms of different elements.
2. They have different atomic numbers.
3. They have the same mass number.
4. They have different physical and chemical properties.
5. Isobars have different number of protons, neutrons as well as electrons.

Question 9. Can different nuclides be possible for an element?

Answer:

Different Nuclides Are Possible For A Particular Element:-

A nuclide is an atomic species characterised by the specific constitution of its nucleus i.e., by its atomic number and mass number. For different isotopes of an element although mass numbers are different but atomic numbers remain same. In this way different nuclides are possible for a particular element. For example, three nuclides for the three possible isotopes of C are \({ }_6^{12} \mathrm{C},{ }_6^{13} \mathrm{C} \text {, }\) \({ }_6^{14} C\).

Question 10. Which of the following are isotones? \({ }_6^{14} C,{ }_7^{14} N,{ }_9^{19} F,{ }_8^{16} O\)

Answer:

Isotones Have The Same Number Of Neutrons:-

Number of neutrons in \({ }_6^{14} \mathrm{C}\) = 14 – 6 = 8

Number of neutrons in \({ }_7^{14} \mathrm{N}\) = 14 – 7 = 7

Number of neutrons in \({ }_9^{19} \mathrm{C}\)= 19 – 9 = 10

Number of neutrons in \({ }_8^{16} \mathrm{O}\) = 16 – 8 = 8

Hence, \({ }_8^{16} \mathrm{O} \text { and }{ }_6^{14} \mathrm{C}\) are isotones.

Question 11. Describe the structure of nucleus of hydrogen isotopes.

Answer:

The Structure Of Nucleus Of Hydrogen Isotopes:-

Three isotopes of hydrogen are protium (\({ }_1^{1} \mathrm{H}\)), deuterium (\({ }_1^{2} \mathrm{H}\)) and tritium (\({ }_1^{3} \mathrm{H}\)).

Protium nucleus contains one proton but no neutron. Deuterium nucleus consists of one proton and one neutron and tritium nucleus contains one proton and two neutrons.

Question 12. Find the number of protons and neutrons in the nuclide \({ }_6^{13} \mathrm{A}\) and write the electronic configuration of the atom. What is the difference between the nuclides \({ }_6^{13} \mathrm{A}\) and \({ }_6^{12} \mathrm{A}\)? Is their chemical property identical?

Answer:

In the nuclide \({ }_6^{13} \mathrm{A}\), number of protons = atomic number = 6.

Number of neutrons = mass number – atomic number = 13 – 6 = 7 .

Number of electrons in the atom = number of protons = 6.

So, the electronic configuration of the atom will be K=2, L = 4.

There are 6 protons and 7 neutrons in the nuclide \({ }_6^{13} \mathrm{A}\). On the other hand, the nuclide \({ }_6^{12} \mathrm{A}\) contains 6 protons and 6 neutrons.

Hence the nuclide \({ }_6^{13} \mathrm{A}\) has 1 neutron more in the nucleus than that in the nuclide \({ }_6^{12} \mathrm{A}\).

Both the nuclides have the same number of protons (they are isotopes). Hence, they will have identical chemical property.

Question 13. What is the relation between F^– , O^2- and Na⁺ ions? Atomic number of F, O and Na are 9, 8 and 11 respectively.

Answer:

Atomic number of F = 9.

Hence, F-atom contains 9 electrons.

Therefore, number of electrons in F² ion = 9 + 1 = 10.

Atomic number of O = 8.

Hence, O-atom contains 8 electrons.

Therefore, number of electrons in O^2- ion = 8 + 2 = 10 .

Atomic number of Na = 11.

Hence, Na-atom contains llelectrons.

Therefore, number of electrons in Na⁺ ion = 11 – 1 = 10 .

All these ions contain the same number of electrons.

These are called isoelectronic species.

Question 14. What is nuclear force? How does this force originate?

Answer:

Nuclear Force:-

The powerful attractive force that acts among the nucleons (protons and neutrons) at a very short range (at a distance of about 1.5 fermi) inside the nucleus is known as nuclear force. It is responsible for holding the nucleons together within the nucleus.

In 1935, scientist Hideki Yukawa proposed ‘meson theory’ to explain the origin of nuclear force. According to this theory, protons and neutrons in the nucleus constantly exchange a small particle called n-meson. Due to the exchange of these meson particles, protons get converted to neutrons and vice-versa.

As a result, the repulsion between protons become insignificant and a strong attractive force is created between the nucleons. This is how the nuclear force originates.

Question 15. Mention the different characteristics of nuclear force.

Answer:

Different Characteristics Of Nuclear Force Are:-

1. Nuclear force is a strong attractive force that holds the nucleons within a close space inside the nucleus.
2. The nature of nuclear force is quite different from that of gravitational force or electrostatic force of attraction.
3. Nuclear force is almost 10⁴⁰ times stronger than gravitational force while it is 100 times stronger than coulombic force.
4. Nuclear force is charge independent. The nature of forces acting between two protons or two neutrons or between a proton and a neutron are identical.
5. This is a very short range force. The force acts within a range of approximately 1 x 10^-15 m within the nucleus. As a result, the force does not exist outside the nucleus.
6. With the help of this force, each nucleon gets attracted only by its nearest neighbouring nucleons.

Question 16. What is Bohr-Bury scheme?

Answer:

Bohr-Bury Scheme:-

1. The Bohr-Bury scheme explains the arrangement of electrons in different orbits around the nucleus. This arrangement is known as electronic configuration. The Bohr-Bury rules regarding electronic configuration of an atom in different orbits are as follows
2. The n -th orbit of an atom accommodates a maximum of 2n² electrons where ‘n’ represents the principal quantum number.
3. The maximum possible number of electrons in the outermost orbit of an atom is 8 irrespective of the principal quantum level.
4. An electron does not occupy a higher energy orbit while a lower energy orbit is left vacant.

Question 17. Is it possible to write the electronic configuration of an atom from the atomic number of the element? Justify your answer.

Answer:

Yes, it is possible to write the electronic configuration of an atom if the atomic number of the element is known.

An atom is electrically neutral and the total positive charge is equal to the total negative charge. Hence, the number of protons in an atom is equal to the number of electrons.

Thus, if atomic number of the element is known, the number of protons as well as number of electrons will be known and hence we can write the electronic configuration of the atom.

Question 18. The atomic number of sodium is 11. Write the electronic configuration of unipositive ion of sodium (Na⁺).

Answer:

The atomic number of sodium is 11. Hence, there are 11 electrons in a sodium atom and its electronic configuration is 2,8,1. Na atom forms Na⁺ ion by releasing an electron from its valence shell. Hence, the electronic configuration of Na⁺ ion is 2,8.

Question 19. Write the electronic configuration of uninegative ion of chlorine (Cl^–).

Answer:

The atomic number of chlorine is 17. Hence, there are 17 electrons in a Cl -atom and its electronic configuration is 2,8,7. Cl-atom forms Cl^– ion by accepting an electron and number of  electrons in its valence shell increases by 1. Thus, the electronic configuration of Cl- ion is 2,8,8.

Question 20. Maximum number of electrons that can be accommodated in M-orbit is 18 but the electronic configuration of potassium (atomic number = 19) cannot be written as 2,8,9. Why?

Answer:

The outermost orbit of an atom cannot actommodate more than 8 electrons. So, M orbit being the outermost orbit can accommodate a maximum of 8 electrons. Thus, the 19th electron of potassium atom enters into N orbit.

Therefore, electronic configuration of potassium atom is 2,8,8,1 and not 2,8,9.

Question 21. The valence shell of an atom is M and it contains 2 electrons. Find the atomic number of the atom and give the name of the element.

Answer:

The valence shell is M and it contains 2 electrons. As the inner orbits are completely filled with electrons, the electronic configuration of the atom is K = 2,L = 8,M = 2 i.e., 2,8,2.

Hence, the number of electrons of the element = number of protons =2 + 8 + 2 = 12.

The atomic number of the element is 12. Hence, the element is magnesium (Mg).

Question 22. How is the chemical reactivity of an element related to its electronic configuration? Explain with example.

Answer:

The chemical reactivity of an element is solely dependent on its electronic configuration.

For example, elements having completely filled outermost orbit are chemically inert.

He (K-2), Ne (K = 2, L = 8), Ar (K = 2, L = 8 . M = 8) have their outermost orbits completely filled with electrons.

Hence, they do not take part in chemical reactions.

Elements having 1, 2, 6 or 7 electrons in their outermost orbit of their atoms are relatively more reactive than other elements. This is why, sodium (K=2, L = 8,M = 1), calcium (K = 2 , L = 8 , M = 8 , N = 2), oxygen (K = 2, L = 6) or chlorine (K = 2, L = 8, M = 7) are chemically very reactive.

Question 23. What happens if the electron of outermost orbit acquires sufficient energy to overcome the attraction of nucleus?

Answer:

If the electron of outermost orbit acquires sufficient energy to overcome the attraction of nucleus, it will move out of the orbit and the atom will be converted to the corresponding cation. The minimum energy required by the outermost electron to overcome the attraction of nucleus is known as the ionisation energy.

Question 24. M³⁺ ion contains 10 electrons and 14 neutrons. Find the atomic number and mass number of the element M. What is the name of the element?

Answer:

The number of electrons in the M³⁺ ion is 10 Here the atom forms a tri-positive ion. So, the number of electrons lost by the atom is 3.

Hence, the number of electrons in M-atom = 10 + 3 = 13.

Therefore, number of protons in M-atom = 13.

So, the atomic number of the element M = 13.

The number of neutrons in M-atom = 14.

Therefore, mass number of the atom = number of protons + number of neutrons = 13 + 14 = 27.

As the atomic number of the element is 13, the element is aluminium (Al).

Quetsion 25. Write the differences between an atom and an ion.

Answer:

The Differences Between An Atom And An Ion Are As Follows:-

Question 26. Number of protons in the nucleus of Ar and Ca are 18 and 20 respectively. Again number of neutrons in those atoms are 22 and 20 respectively. What is the relation between them?

Answer:

Mass number of Ar = 18 + 22 = 40 Mass number of Ca = 20 + 20 = 40

∴  The nuclides are \({ }_{18} \mathrm{Ar}^{40}\) and \({ }_{20} \mathrm{Ca}^{40}\).

The two nuclides have the same mass number but their atomic numbers are different. Hence they are isobars.

Question 27. Write down the differences between isotones and isobars.

Answer:

The Differences Between Isotones And Isobars Are As Follows:-

Question 28. State rationally whether chemical properties of the following nuclides are same or different: \({ }_{Z-1}^A M \text { and }{ }_{Z-1}^{A+1} N\)

Answer:

For the two nuclides, atomic numbers are same, i.e., (Z- 1) but mass numbers are different which indicates that they are isotopes. Hence they possess identical electronic configuration as well as similar chemical properties .

Question 29. Calculate the number of electrons in \({ }_{92} U^{235}\). How will you write the atom if it contains three more neutrons? What will be the relation between the two mentioned atom?

Answer:

1. In \({ }_{92} U^{235}\), number of protons = 92. Hence, the number of electrons = 92 .
2. If there is 3 more neutrons, the nuclide will be = \({ }_{92}^{238} U\)
3. \({ }_{92} U^{235}\) and \({ }_{92}^{238} U\) are isotopes of element U.

Question 30 If \({ }_b^a X \text { and }{ }_d^c Y\) are isotopes to each other, prove that (a² + c²)(b² – d²) = 0.

Answer:

Since, \({ }_b^a X \text { and }{ }_d^c Y\) are isotopes to each other, so b = d or, b² = d² or, (b² – d²) = 0

or, (a² + c²)(b² – d²) = 0 x (a² + c²) [(a² + c²) ≠ 0]

or, (a² + c²)(b² – d²) = 0 (Proved)

Question 31. How will you express the nucMtte formed by removal of 3 neutrons from \({ }_{92} U^{238}\)?What will be the number of neutrons in the new nuclide? Depict the relation between the old and new nuclides.

Answer:

Mass no. of the new nuclide = 238 – 3 = 235

∴ The new nuclide will be expressed as \({ }_{92} U^{235}\)

Number of neutrons in \({ }_{92} U^{235}\)=235-92 =143

⇒ \({ }_{92} U^{235}\) and \({ }_{92} U^{238}\) are two isotopes of uranium.

Question 32. If \({ }_a X^c,{ }_b Y^d\) are isotopes and \(m^{A^n}, p^{B^q}\) are isobars to each other, calculate (a²-b²)(n-q) = ?

Answer:

Since \({ }_a X^c,{ }_b Y^d\) are isotopes to each other, so a = b or, (a – b) = 0

Since \({ }_m A^n \text { and }{ }_p B^q\) are isobars to each other, so n = q or, (n – q) = 0

Now, (a² – b²)(n – q) = (a + b)(a – b)(n – q) = (a + b) x 0 x 0 = 0

Question 33. Mass numbers of the atoms X, Y and Z are 31, 32 and 34 respectively. Their atomic numbers are 15,16 and 16 respectively. Identify the isotopes and isotones among them.

Answer:

Corresponding nuclides are \({ }_{15} X^{31},{ }_{16} Y^{32}\) and \({ }_{16} Z^{34}\).

Atomic numbers of Y and Z are equal but they have different mass numbers.

∴ Y and Z are isotopes.

Again no. of neutrons in \({ }_{15} X^{31}\) = 31 – 15 = 16

and no. of neutrons in \({ }_{16} Y^{32}\) = 32 – 16 = 16

∴ Number of neutrons are same in X and Y but their mass numbers are different.

∴ X and Y isotones.

Question 34. An atom contains 2 electrons in outermost M orbit. What are the atomic number and name of the element?

Answer:

The outermost orbit of the atom is M and it contains 2 electrons.

∴ Electronic configuration will be 2,8,2.

∴ Atomic no. of the element = total no. of protons = total no of electrons = 2 + 8 + 2 = 12

Since atomic number is 12, the corresponding element is Mg, i.e., magnesium.

Question 35. An element contains two electrons in its valence N shell, identify the element.

Answer:

Electronic configuration of the element is K(2), 1(8), M(8), N(2).

∴ Atomic number of the element = 2 + 8 + 8 + 2 = 20.

∴ The corresponding element is calcium (₂₀Ca).

Question 36. Write down the electronic configuration of \({ }_{8} O^{16}\) and \({ }_{12} Mg^{24}\).

Answer:

Electronic configuration of ₈O¹⁶ is K(2), L(6).

Electronic configuration of ₁₂Mg²⁴ is K(2), L(8), M(2).

Question 37. Atomic number of an element is 20. Write down its electronic configuration. What is the valency of the element?

Answer:

Electronic configuration of the element = K(2) , L(8), M(8), N(2)

Since the outermost N orbit of the element contains 2 electrons, the valency of the element is 2.

Question 38. Which one is more stable in between atoms and ions and why?

Answer:

Ions are more stable than atoms. When an atom gets converted to the corresponding ion it attains a stable electronic configuration similar to that of the nearest inert gas. For example, electronic configuration of Cl -atom is K(2), 1(8), M(7) and electronic configuration of Cl^Θ ion is K(2), L(8), M(8).

Hence, the electronic configuration of Cl^Θ ion is identical to the electronic configuration of Ar-atom. Therefore, Cl^Θ is more stable than Cl -atom.

Question 39. Write down the relation between the nuclides: \({ }_A P^B \text { and }{ }_A Q^{B+1}\) and \({ }_A+1 R^{B+1}\)

Answer:

For \({ }_A P^B \text { and }{ }_A Q^{B+1}\), atomic numbers are equal while mass numbers are different.

∴ \({ }_A P^B \text { and }{ }_A Q^{B+1}\) are isotopes to each other.

For \({ }_A Q^{B+1}\) and \({ }_A+1 R^{B+1}\), mass numbers are equal while atomic numbers are different.

∴ \({ }_A Q^{B+1}\) and \({ }_A+1 R^{B+1}\) are isobars to each other.

For \({ }_A P^B\) and \({ }_A+1 R^{B+1}\), number of neutrons are equal to (B-A).

∴ \({ }_A P^B\) and \({ }_A+1 R^{B+1}\) are isotones to each other.

Question 40. Which one of K atom and K^⊕ ion acts violently with water and why?

Answer:

Electronic configuration of K -atom = 2, 8, 8, 1.

This K-atom loses one electron to form K^⊕ ion, electronic configuration of which is similar to that of noble gas Ar. Due to this, K^⊕ ion is more stable than K-atom. Hence, K-atom reacts more violently with water to form potassium hydroxide and hydrogen gas.

Questiobn 41. Write down the name of a cation and an anion whose electronic configuration is similar to that of Ne.

Answer:

Electronic configuration of Ne = 2,8.

∴ Cation and anion with similar electronic configurations are \({ }_{11} \mathrm{Na}^{\oplus} \text { and }{ }_9 \mathrm{~F}^{\ominus}\) respectively.

Chapter 4 Matter Nuclear Force Very Short Answer Type Questions Choose The Correct Answer

Question 1. \({ }_1^2 \mathrm{H} \text { and }{ }_2^3 \mathrm{He}\) are

1. Isotope
2. Isobars
3. Isotones
4. None of these

Answer: 3. Isotones

Question 2. The number of isotopes of oxygen is

1. 3
2. 4
3. 1
4. 2

Answer: 1. 3

Question 3. An element which has no isotope is

1. Carbon
2. Chlorine
3. Fluorine
4. Oxygen

Answer: 3. Fluorine

Question 4. The electronic configuration of Ca²⁺ ion is

1. 2, 8, 8
2. 2, 8, 8, 2
3. 2, 8, 8, 1
4. 2, 8, 7

Answer: 1. 2, 8, 8

Question 5. The isotope of carbon which is used for radiocarbon dating is

1. \({ }_6^{12} \mathrm{C}\)
2. \({ }_6^{13} \mathrm{C}\)
3. \({ }_6^{14} \mathrm{C}\)
4. \({ }_6^{15} \mathrm{C}\)

Answer: 3. \({ }_6^{14} \mathrm{C}\)

Question 6. Isotopes of an element possess

1. Identical physical properties
2. Different chemical properties
3. Different number of neutrons
4. Different atomic numbers

Answer: 3. Different number of neutrons

Question 7. Isotopes contain equal number of

1. Neutrons
2. Protons
3. Positrons
4. Mesons

Answer: 2. Protons

Question 8. Isobars have identical

1. Atomic number
2. Number of protons
3. Number of electrons
4. Mass number

Answer: 4. Mass number

Question 9. Isotones have identical

1. Number of electrons
2. Number of protons
3. Number of neutrons
4. Number of positrons

Answer: 3. Number of neutrons

Question 10. For isotopes, a slight difference is observed in case of their

1. Actual mass
2. Atomic number
3. Number of electrons
4. Number of protons

Answer: 1. Actual mass

Question 11. Protons and neutrons of an atom are collectively known as

1. Positron
2. Isotope
3. Nucleon
4. Isobar

Answer: 3. Nucleon

Question 12. Which of the following is exchanged between protons and neutrons for the generation of nuclear force

1. α -particle
2. β-particle
3. Positron
4. Meson

Answer: 4. Positron

Question 13. The range within which nuclear force acts is

1. 1.5 fermi
2. 2.5 fermi
3. 3.5 fermi
4. 4.5 fermi

Answer: 1. 1.5 fermi

Question 14. The number of electrons in Cl^– ion is

1. 19
2. 18
3. 20
4. 15

Answer: 2. 18

Question 15. Maximum number of electrons that can be accommodated in the valence shell of an atom is

1. 18
2. 10
3. 2
4. 8

Answer: 4. 8

Question 16. Which of the following noble gases does not contain 8 electrons in its valence shell?

1. Ne
2. Ar
3. Xe
4. He

Answer: 4. He

Question 17. The atoms and ions with equal number of electrons are known as

1. Isotopes
2. Isobars
3. Isotones
4. Isoelectronic

Answer: 4. Isoelectronic

Question 18. Number of electrons in S^2- ion

1. 15
2. 16
3. 17
4. 18

Answer: 4. 18

Question 19. The element which does not contain 8 electrons in the outermost orbit

1. Ar
2. Ne
3. Pd
4. None of these

Answer: 3. Pd

Question 20. Mg²⁺, O^2-, Ne, F^– have identical

1. Mass number
2. No. of protons
3. No. of electrons
4. No. of neutrons

Answer: 3. No. of electrons

Question 21. Number of electrons in the outermost orbit of \({ }_{15}^{31} p\) is

1. 2
2. 3
3. 5
4. 6

Answer: 3.5

Question 22. From which orbit of Al, electrons are removed to form Al³⁺ ?

1. K
2. L
3. M
4. N

Answer: 3. M

Question 23. Difference in the number of electrons in L and M orbits of Na atom is

1. 8
2. 7
3. 9
4. 6

Answer: 2. 7

Question 24. Which pair of the following is isoelectronlc?

Na⁺, O^–

Na⁺, Mg²⁺

He⁺, K⁺

Mg²⁺,O^–

Answer: 2. Na⁺, Mg²⁺

Question 25. Relation between \({ }_{15}^{31} P\) and \({ }_{16}^{32} S\) is

1. Isotope
2. Isobar
3. Isotone
4. Isomer

Answer: 3. Isotone

Question 26. Electronic configuration of ₁₁Na is

1. 1, 2, 8
2. 2, 1, 8
3. 8, 2, 1
4. 2, 8, 1

Answer: 4. 2, 8, 1

Question 27. Which one of the following has equal number of electrons to that of Be²⁺?

1. H⁺
2. He
3. He²⁺
4. Na⁺

Answer: 2. He

Question 28. Which one of the following is an isotope of hydrogen?

1. Helium
2. Deuterium
3. Beryllium
4. Calcium

Answer: 2. Deuterium

Chapter 4 Matter Nuclear Force Answer In Brief

Question 1. Who discovered radioactivity?

Answer: French scientist Henri Becquerel.

Question 2. Identify the isotopes and isobars from the following

1. 8p + 8n,
2. 8p + 9n,
3. 18p + 22n,
4. 20p + 20n (p = proton, n = neutron).

Answer: 1 and 2 have the same number of protons. So, they are isotopes of the same element, 3 and 4 have the same mass number. Hence, they are isobars.

Question 3. Which isotope of carbon is radioactive?

Answer: \({ }_6^{14} C\) isotope of carbon is radioactive.

Question 4. What similarities are observed In the isotopes of an element?

Answer: All the isotopes of an element have the same atomic number and identical chemical properties.

Question 5. What similarities are observed in isobars?

Answer: Isobars have the same mass number.

Question 6. What similarities are observed in isotones?

Answer: Isotones contain same number of neutrons in their nucleus.

Question 7. Exchange of which particle between protons and neutrons is responsible for the generation of nuclear force?

Answer: Exchange of meson particles .

Question 8. Who explained the formation of nuclear force?

Answer: Scientist Yukawa.

Question 9. What is meant by valence shell of an atom?

Answer: The outermost orbit of an atom is known as the valence shell of that atom.

Question 10. Name the inert gas which has two electrons in its valence shell.

Answer: Helium (He) is the inert gas which has two electrons in its valence shell.

Question 11. State the maximum number of electrons that can be accommodated by the valence shell of an atom.

Answer: The maximum number of electrons that can be accommodated by the valence shell of an atom is 8.

Question 12. What is meant by electronic configuration of an atom?

Answer: In a multi-electron atom, the definite arrangement of electrons in different orbits around the nucleus is known as its electronic configuration.

Question 13. What is the maximum possible number of electrons that can be accommodated by the M-orbit of an atom?

Answer: The M-orbit of an atom can accommodate a maximum of 18 electrons.

Question 14. Who was the first to observe the difference in number of neutrons in different atoms of the same element (or the existence of isotopes)?

Answer: Scientist Soddy.

Question 15. Which isotope of hydrogen is radioactive in nature?

Answer: Tritium (\({ }_1^3 \mathrm{H}\)).

Question 16. Which isotope of hydrogen is present in heavy water?

Answer: Deuterium (\({ }_1^2 \mathrm{H}\)) is present in heavy water (D20).

Question 17. Which isotope of chlorine is abundantly found in nature?

Answer: Chlorine has two isotopes, \({ }_{17}^{35} \mathrm{Cl} \text { and }{ }_{17}^{37} \mathrm{Cl}\), out of which \({ }_{17}^{35} \mathrm{Cl}\) is abundantly found in nature (almost 75%).

Question 18. Which isotope of oxygen is abundantly found in nature?

Answer: Oxygen has three isotopes, \({ }_8^{16} O,{ }_8^{17} O\) and \({ }_8^{18} O\), out of which \({ }_8^{16} O\) is abundantly found in nature.

Question 19. Give an example of an element which has no naturally occurring isotope.

Answer: Elements such as fluorine (F) and sodium (Na) have no naturally occurring isotope.

Question 20. Give an example of an isotope in which the number of protons is greater than the number of neutrons.

Answer: In an isotope of helium, \({ }_2^3 \mathrm{He}\) there are two protons and one neutron, i.e., in case of this than the number of neutrons.

Question 21. Which element has the maximum number of stable isotopes?

Answer: Tin (Sn) has the maximum number (10) of stable isotopes.

Question 22. What is the charge of an Na⁺ ion?

Answer: The charge of an Na⁺ ion is +1.602 x 10^-9 coulomb (it is equal to the charge of an electron but is opposite in nature).

Question 23. What is the charge of an O^2- ion?

Answer: The charge of an O^2- ion is -2 x 1.602 x 10^-19 coulomb or -3.204 x 10^-19 coulomb.

Question 24. From which orbit of Al electrons are removed to form Al³⁺ ion?

Answer: From M-orbit (outermost orbit for Al) of Aluminium 3 electrons are removed to form Al³⁺ ion.

Question 25. Give an example of isobar of \({ }_7 N^{14}\).

Answer: \({ }_6 C^{14}\)

Question 26. What is the relation between F^–, O^2- and Na^⊕ ions?

Answer: F^–, O^2- and Na^⊕ ions are isoelectronic.

Question 27. How does the energy of an orbit vary with increasing distance from nucleus?

Answer: Energy of an orbit increases with the increase in distance from the nucleus.

Question 28. An atom has three orbits. The third orbit contains 5 electrons. What is its atomic number?

Answer: Hence, the electronic configuration of the atom is K(2), 1(8), M(5).

∴ Its atomic number is (2 + 8 + 5) = 15.

Question 29. If \({ }_b^d X \text { and }{ }_d Y\) are isotopes to each other, write down the relation between b and d.

Answer: b = d

Question 30. How many electrons are there in the M- shell of potassium (Z = 19) ?

Answer: Electronic configuration of potassium is K(2), L(8), M(8), A/(l). So number of electron in M-shell is 8.

Question 31. Write down the electronic configuration of S^– ion.

Answer: K(2), L(8), M(7).

Question 32. Which subatomic particle is responsible for formation of isotope?

Answer: Neutron.

Question 33. Calculate the number of electrons in Mg²⁺ ion.

Answer: Atomic number of Mg = 12 .

∴ Number of electrons in Mg²⁺ ion = 12-2 = 10.

Question 34. Write down the electronic configuration of Na⁺ ion.

Answer: Electronic configuration of ₁₁Na⁺ is K(2), L(8).

Question 35. What is the possible maximum number of electrons in the n-th orbit of an atom?

Answer: Possible maximum number of electrons in the n-th orbit of an atom is 2n².

Question 36. What is formed when electrons are removed from an atom?

Answer: Positively charged ion or cation is formed when electrons are removed from the outermost shell of an atom.

Chapter 4 Matter Nuclear Force Fill in the Blanks

Question 1. Isotopes are identical with respect to their ______ properties.

Answer: Chemical

Question 2. Isobars have the same ________ number.

Answer: Mass

Question 3. Isotones contain equal number of ________

Answer: Neutrons

Question 4. Nuclear force operates within a range of ______ m.

Answer: 1.5 x 10^-15

Question 5. Nuclear force originates due to the exchange of __________ particles between protons and neutrons.

Answer: Meson

Question 6. Most of the naturally occurring elements exist as a mixture of two or more of their ______

Answer: Isotopes

Question 7. Isotopes of an element have the ________ electronic configuration.

Answer: Same

Question 8. Electronic configurations of isobars are ________

Answer: Different

Question 9. Except helium, all other noble gases contain __________ electrons in their valence shell.

Answer: 8

Question 10. The filling of electrons in their respective orbits obeys the _________ rule.

Answer: Bohr Burry

Chapter 4 Matter Nuclear Force State Whether True Or False

Question 1. The n-th orbit around the nucleus can accommodate a maximum of 2n² electrons.

Answer: True

Question 2. Isotopes are atoms of the same element with the same atomic number but different mass numbers.

Answer: True

Question 3. The M-orbit of an electron can accommodate a maximum of 8 electrons.

Answer: False

Question 4. Atomic numbers of elements P and Q are 18 and 20 respectively whereas their mass number is 40. P and Q are isotones.

Answer: False

Question 5. Ionisation energy is the minimum amount of energy required by an electron to overcome the attraction of the nucleus.

Answer: True

Question 6. Nuclear force is a long range force.

Answer: False

Question 7. Outermost orbit of neon does not contain 8 electrons.

Answer: False

Question 8. \({ }_{14}^{30} S e,{ }_{15}^{31} p,{ }_{16}^{32} S\) are isobars to each other.

Answer: False

Question 9. Isoelectronic anion of Na+ is F^–.

Answer: True

Question 10. Actual mass of isobars are not same.

Answer: True

Question 11. Number of neutrons in isotopes are same.

Answer: False

Question 12. Chemical properties of isobars are same.

Answer: False

Chapter 4 Matter Nuclear Force Miscellaneous type Questions

Match The Columns

1.

Answer: 1. D, 2. C, 3. B, 4. A

2.

Answer: 1. C, 2. A, 3. D, 4. B

3. 

Answer: 1. C, 2. A, 3. D, 4. B