Which has a larger radius: Cl or Cl − ? Why?

📚 Chapter: Classification of Elements and Periodicity in Properties

📘 Detailed Explanation

🔵 Answer

Cl⁻ has a larger radius than Cl.

A neutral chlorine atom Cl has 17 protons and 17 electrons. When it gains one electron, it forms the chloride ion Cl⁻, which has 17 protons but 18 electrons.

Cl < Cl⁻

⚛️ Why is Cl⁻ larger?

1. Cl gains one electron to form Cl⁻.
2. The nuclear charge remains the same because the number of protons remains 17.
3. The number of electrons increases from 17 to 18.
4. Electron-electron repulsion increases.
5. The increased repulsion causes the electron cloud to expand.
6. Therefore, the ionic radius of Cl⁻ is greater than the atomic radius of Cl.

Cl + e⁻ → Cl⁻

17 protons + 17 electrons → 17 protons + 18 electrons

📊 Comparison

Species	Protons	Electrons	Relative Radius
Cl	17	17	Smaller
Cl⁻	17	18	Larger

🔬 Electronic Configuration

Cl (Z = 17):

2, 8, 7

Cl⁻ (18 electrons):

2, 8, 8

Cl⁻ has a completely filled third shell with 8 electrons. The additional electron increases electron-electron repulsion, resulting in a larger electron cloud.

✅ Final Answer

Cl⁻ has a larger radius than Cl because chlorine gains one electron to form Cl⁻ while its nuclear charge remains unchanged. The extra electron increases electron-electron repulsion, causing the electron cloud to expand.

Cl < Cl⁻

📝 20 MCQs with Answers

1. Which has a larger radius?

A) Cl

B) Cl⁻

C) Both are equal

D) Cannot be determined

✅ Answer

B) Cl⁻

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2. Cl⁻ is formed when Cl:

A) Loses one electron

B) Gains one electron

C) Loses one proton

D) Gains one proton

✅ Answer

B) Gains one electron

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3. Atomic number of chlorine is:

A) 15

B) 16

C) 17

D) 18

✅ Answer

C) 17

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4. Number of electrons in neutral Cl is:

A) 16

B) 17

C) 18

D) 19

✅ Answer

B) 17

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5. Number of electrons in Cl⁻ is:

A) 16

B) 17

C) 18

D) 19

✅ Answer

C) 18

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6. During formation of Cl⁻, the number of protons:

A) Increases

B) Decreases

C) Remains unchanged

D) Becomes zero

✅ Answer

C) Remains unchanged

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7. The larger radius of Cl⁻ is mainly due to:

A) Increased nuclear charge

B) Increased electron-electron repulsion

C) Decreased number of electrons

D) Loss of a shell

✅ Answer

B) Increased electron-electron repulsion

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8. Which species has the electronic configuration 2,8,8?

A) Cl

B) Cl⁻

C) Na

D) F

✅ Answer

B) Cl⁻

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9. Cl⁻ is a:

A) Cation

B) Anion

C) Neutral atom

D) Molecule

✅ Answer

B) Anion

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10. Which has more electrons?

A) Cl

B) Cl⁻

C) Both equal

D) Neither

✅ Answer

B) Cl⁻

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11. An anion is generally ______ than its neutral atom.

A) Smaller

B) Larger

C) Equal

D) Zero

✅ Answer

B) Larger

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12. Which statement is correct?

A) Cl has 18 electrons

B) Cl⁻ has 17 electrons

C) Cl⁻ has 18 electrons

D) Cl⁻ has 19 protons

✅ Answer

C) Cl⁻ has 18 electrons

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13. Which factor remains unchanged when Cl becomes Cl⁻?

A) Number of electrons

B) Number of protons

C) Electron-electron repulsion

D) Ionic charge

✅ Answer

B) Number of protons

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14. The charge on Cl⁻ is:

A) +1

B) −1

C) +2

D) 0

✅ Answer

B) −1

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15. The valence shell of Cl contains:

A) 5 electrons

B) 6 electrons

C) 7 electrons

D) 8 electrons

✅ Answer

C) 7 electrons

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16. Cl⁻ has a stable configuration similar to:

A) He

B) Ne

C) Ar

D) Kr

✅ Answer

C) Ar

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17. Which order is correct?

A) Cl⁻ < Cl

B) Cl < Cl⁻

C) Cl = Cl⁻

D) Cl⁻ = nucleus

✅ Answer

B) Cl < Cl⁻

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18. The formation of Cl⁻ involves:

A) Oxidation

B) Reduction

C) Sublimation

D) Neutralisation only

✅ Answer

B) Reduction

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19. Which statement explains the larger radius of Cl⁻?

A) Same nuclear charge attracts more electrons

B) Nuclear charge doubles

C) Protons are lost

D) Electrons disappear

✅ Answer

A)

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20. The best conclusion is:

A) Cations are always larger than atoms

B) Anions are generally larger than their parent atoms

C) Ion formation does not affect radius

D) Cl⁻ is smaller than Cl

✅ Answer

B)

Q. Which has a larger radius: Cl or Cl⁻? Give reason.

Solution:

Cl⁻ has a larger radius than Cl. Chlorine gains one electron to form Cl⁻. The nuclear charge remains the same, but electron-electron repulsion increases due to the additional electron, causing expansion of the electron cloud.

Cl < Cl⁻

Q. Explain why the radius of Cl⁻ is greater than that of Cl.

Solution:

1. Cl has 17 protons and 17 electrons.
2. Cl⁻ has 17 protons and 18 electrons.
3. The nuclear charge remains unchanged, while electron-electron repulsion increases.
4. This repulsion expands the electron cloud, making Cl⁻ larger.

Therefore, Cl⁻ > Cl in radius.

Q. Compare Cl and Cl⁻ in terms of their electronic configuration and radius.

Property	Cl	Cl⁻
Protons	17	17
Electrons	17	18
Electronic configuration	2, 8, 7	2, 8, 8
Radius	Smaller	Larger

The additional electron in Cl⁻ increases electron-electron repulsion while the nuclear charge remains unchanged. Therefore, the electron cloud expands.

Cl < Cl⁻

Q. Explain the difference between the atomic radius of Cl and the ionic radius of Cl⁻.

Solution:

Neutral chlorine has atomic number 17 and therefore contains 17 protons and 17 electrons. Its electronic configuration is 2,8,7.

When chlorine gains one electron, it forms Cl⁻. The ion now contains 17 protons and 18 electrons, with configuration 2,8,8.

The nuclear charge remains constant because no proton is added. However, the extra electron increases electron-electron repulsion. Consequently, the electron cloud expands and the ionic radius becomes larger.

Cl + e⁻ → Cl⁻
Electron count: 17 → 18

Hence, the radius of Cl⁻ is greater than the radius of Cl.

Q. Which has a larger radius, Cl or Cl⁻? Explain in detail using nuclear charge, number of electrons and electron-electron repulsion.

Detailed Solution

Chlorine has atomic number Z = 17. Therefore, a neutral chlorine atom contains 17 protons and 17 electrons.

Cl: 17 protons + 17 electrons → 2,8,7

When chlorine gains one electron, it forms the chloride ion:

Cl + e⁻ → Cl⁻
Cl⁻: 17 protons + 18 electrons → 2,8,8

Why does the size increase?

1. The number of protons remains 17.
2. The number of electrons increases from 17 to 18.
3. The same nuclear charge now attracts more electrons.
4. Electron-electron repulsion increases.
5. The electron cloud expands.
6. Therefore, Cl⁻ has a larger radius than Cl.

Species	Protons	Electrons	Radius
Cl	17	17	Smaller
Cl⁻	17	18	Larger

🎯 Final Answer:

Cl⁻ has a larger radius than Cl. When Cl gains an electron, the nuclear charge remains unchanged, but electron-electron repulsion increases. This expands the electron cloud and increases the ionic radius.

Cl < Cl⁻

🎯 Quick Revision

Cl: 17 e⁻ → 2,8,7
Cl⁻: 18 e⁻ → 2,8,8
Protons: Same = 17
Electron Repulsion: Increases in Cl⁻

Cl < Cl⁻