Question

257. Ionization energy decreases down the group due to

• A. increase in charge
• B. increase in atomic size
• C. decrease in size
• D. decreasing in shielding effect

Answer 1

The correct option is B

increase in atomic size

Ionization energy is the measure of the force of attraction between the nucleus and the valence electrons. In other words, it is the amount of energy required to remove an electron from an isolated atom or molecule.

Explanation of the correct option:

(B) increase in atomic size:

• As we move down the group, ionization energy decreases because while moving down the group atomic size increases due to this fact the force of attraction between the nucleus and the valence electrons is weaker.
• So, it becomes easy to remove an electron from an atom.
• Thus, the ionization decreases down the group.

Explanation of the incorrect option:

(A) increase in charge:

• As we move down the group nuclear charge increases but the shielding effect reduces the effective nuclear charge per electron. So, the increased nuclear charge has not much effect on ionization energy while moving down the group.

(C) decrease in size:

• As we move down the group the size of the atom increases because the number of shells increases and the distance between the nucleus and valence shell increases which results in increased atomic size.

(D) decreasing in shielding effect:

• Shielding effect: When the number of inner electrons is more than valence electrons then the valence electrons experience a lesser force of attraction from the nucleus. This is called the shielding effect.
• As we move down the group there is the addition of new shells which increases the shielding effect.

Hence, option (B) is correct and Ionization energy decreases down the group due to increase in atomic size