Question

Fluorine has the highest electronegativity among the $n s^{2}$ $n p^{5}$ group on the Pauling scale, but the electron affinity of fluorine is less than that of chlorine because

• A. the atomic number of fluorine is less than that of chlorine
• B. fluorine being the first member of the family behaves in an unusual manner
• C. chlorine can accommodate an electron better than fluorine by utilising its vacant $3 d$ -orbital
• D. small size, high electron density and an increased electron repulsion makes addition of an electron to fluorine less favourable than that in the case of chlorine.

Answer 1

Answer: (C)

A valence-electron in a multi-electron atom is attracted by the nucleus and repelled by the electrons of inner-shells. The combined effect of this attractive and repulsive force acting on the valence-electron experiences less attraction from the nucleus. This is called shielding or screening effect.
In Cl, there are empty d-orbitals where it can accommodate its electron and because of this, attraction forces increases and electron affinity also.