QS Study

Factors affecting electron affinity

(1) Atomic size

Electron affinity α [1/Size of atom]

Smaller the size of an atom, greater is its electron affinity. As the size of atom increases, the effective nuclear charge decreases or the nuclear attraction for adding electron decreases. Consequently, atom will have less tendency to attract additional electron towards itself.

Therefore, Electron affinity α Effective nuclear charge. In general, electron affinity decreases in going down the group and increases in going from left to right across the period. On moving down the group atomic size increases and on going from left to right in a period atomic size decreases.

(2) Shielding or Screening Effect

Electron affinity α [1/Shielding effect]

Electronic energy state, lying between nucleus and outermost state hinder the nuclear attraction for incoming electron. Therefore, greater the number of inner lying state, less will be the electron affinity.

(3) Electronic Configuration – The electronic configurations of elements influence their electron affinities to a considerable extent.

Electron affinities of inert gases are zero. This is because their atoms have stable ns2 np6 configuration in their valence shell and there is no possibility for addition of an extra electron.

Electron affinity of beryllium, magnesium and calcium is practically zero. This is attributed to extra stability of the fully completed s-orbitals in them. Thus, if an atom has fully filled or half filled orbitals, its electron affinity will be low.