Question

Fluorine has the highest electronegativity among the $ns^{2} np^{5}$ 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 3d-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.