Electron Affinity

Electron affinity may be defined as, “The amount of energy released when an isolated gaseous atom accepts an electron to form monovalent gaseous anion.”

The process can be expressed as;

X (g)     +       e^–  −−−−−−>   X^– (g)   +   Energy (E. A.)

The value of Electron Affinity (E.A) measures the tendency of an atom to accept an electron.

SUCCESSIVE ELECTRON AFFINITIES

When the first electron is added to the gaseous atom, it forms a Uninegative ion and the energy released is called First Electron Affinity (E.A₁).Now if an electron is added to the uninegative ion, it experiences a repulsive force from an anion. As a result, the energy has to be supplied to overcome the repulsive force. Thus, in order to add the second electron energy is required rather than released. Therefore, the value of second Electron affinity is negative. Similarly, addition of 3^rd, 4^th electrons etc. also requires energy. Thus, the values of successive electron affinities (EA₂, EA₃ ……) are negative.