(solved)Question 3.24 of NCERT Class XI Chemistry Chapter 3

$\displaystyle \underline{\underline{\text{Part (a)}}}$

The newly added electron is added to the valence shell and anion is formed.

Mutual repulsion between the electrons of the valence shell increases, which causes the size to increase.

Effective nuclear charge decreases because of the increased mutual shielding, which causes the size to increase.

Addition of a new electron may cause it be added to a new principal shell - leading to a significant increase in size.

Examples: F atom is 40 pico-m and F^- is 130 pico-m.

$\displaystyle \underline{\underline{\text{Part (b)}}}$

The newly removed electron leads to a cation.

Mutual repulsion decreases between the electrons of the valence shell, leading to a decrease in size.

Effective nuclear charge increases because of less mutual shielding, which causes the size to decrease.

Addition of a new electron may cause it be removed from a principal shell - leading to a significant decrease in size.

Examples: Li atom is 165 pico-m and Li⁺ is 75 pico-m.