CBSE Class 11-science Answered

Electron affinity or electron gain enthalpy is the amount of energy released when an electron is added to an isolated gaseous atom.

Electron affinity is the ability of an atom to hold an additional electron. If the atom has more tendency to accept an electron then the energy released will be large and consequently the electron affinity will be high. Electron affinities can be positive or negative. It is taken as positive when an electron is added to an atom. It is expressed as electron volts per atom (eV per atom) or kilo joules per mole.

Electron affinity depends on:

i) Extent of nuclear charge

ii) Size of the atom

iii) Electronic configuration.

As a result of the gain in electrons, the atom gains one negative charge. In the case of halogens, all the elements have a high electron affinity, as they need one electron to complete the octect of their outermost shell.