NIOS Class 12 Chemistry Chapter 18 General Characteristics of the p-block Elements

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NIOS Class 12 Chemistry Chapter 18 General Characteristics of the p-block Elements

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General Characteristics of the p-block Elements

Chapter: 18

Module – VI: Chemistry of Elements

INTEXT QUESTIONS 18.1

1. Which of the following atoms is expected to have smaller size?

(i) ₉F and ₁₇CI.

(ii) ₆C and ₁₄Si.

(iii) ₅B and ₆C.

(iv) ₆C and ₇N.

Ans: (i) ₉F (ii) ₆C (iii) ₆C (iv) ₇N.

2. Which atom in the following pairs of atoms is expected to have higher ionization enthalpy?

(i) ₄Be and ₅B. 

(ii) ₁₆S and ₁₇CI.

(iii) ₂He and ₁₀Ne.

(iv) _😯 and ₁₆S.

Ans: (i) ₄Be (ii) ₁₇Cl (iii) ₂He (iv) ₈O.

3. Arrange the following atoms in order of increasing ionization enthalpy: ₂He,₄Be, ₇N, ₁₁Na.

Ans: Na < Be < N < He.

4. How does the ionization enthalpy vary in general in a group and in a period of the p-block elements?

Ans: In a group, it decreases down the group and it usually increases along a period.

INTEXT QUESTIONS 18.2

1. Why does fluorine have electron gain enthalpy lower than chlorine?

Ans: The unexpectedly low value of electron gain enthalpy for F as compared to that of Cl atom may be attributed to the extremely small size of F atom visa-vis Cl atom. The addition of an electron produces a negative ion which has a high electron density and leads to increased interelectronic repulsions.

2. Which atom in the following pair of atoms has greater electron gain enthalpy?

(i) F, Cl

(ii) Br, I 

(iii)I, Xe

(iv) O, F 

(v) O,S

Ans: (i) Cl (ii) Br (iii) I (iv) F (v) S

3. Give two reasons for the fact that the first element in each group of p-block exhibits unique behaviour.

Ans: (i) Small size (ii) absence of d-orbitals.

4. Explain why oxygen exists as a gas whereas sulphur exists as a solid.

Ans: Because oxygen can form multiple bonds (O = O).

5. Mention two reasons which are responsible for the so called “inert pair effect”.

Ans: (i) Lower bond energy in the compounds of heavier atoms and.

(ii) the higher energy involved in promotion from the ground state (s²p¹) to the valence state (s¹p²).

6. What is the consequence of “inert pair effect” on the oxidation states of Tl and Pb?

Ans: Lower oxidation states become more stable. For Tl, +1 and for Pb, +2.

INTEXT QUESTION 18.3

1. Which of the following oxides is the most acidic?

(i) Al2₂O₃

(ii) CO₂

(iii) SO₂

Ans: (iii) SO₂

2. Which of the following hydrides of main group elements is the most acidic?

(i) H₂Se

(ii) H₂O

(iii) HCI

(iv) HI

Ans: (iv) HI.

3. Arrange the following in the increasing order of covalent character.

SiCl₄, CCl₄, SnCl₄, GeCl₄.

Ans: SnCl₄ < Ge Cl₄ < SiCl₄ < CCl₄

4. What happens when SiCl₄ reacts with water? Write complete chemical equation for the reaction.

Ans: SiCl₄+ 4H₂O → Si(OH)₄ + 4HCl

5. How do the bond angles vary among the following hydrides NH₃, PH₃, AsH₃, SbH₃.

Ans: The bond angle decreases from 107º to almost 90º.

6. Give equations for the formation of the following from the elements:

(i) Al₂O₃

(ii) SiCl₄

(iii) CCl₄

Ans: (i) 4Al(s) + 3O₂(g) → 2Al₂O₃ (s)

(ii) Si(s) + 2Cl₂(g) → SiCl₄(l)

(iii) C(s) + 2Cl₂(g) → CCl₄(l)

7. Which is more covalent in each of the following pairs?

(i) AlCl₃ and BCl₃

(ii) PbCl₂ and PbCl₄

Ans: (i) BCl₃

(ii) PbCl₄