Q. How to Determine Electron Affinity?

Ans.

Electron affinity is the measure of an atom's tendency to form a negative ion.

Electron affinity can be measured by the amount of energy released when an electron is added to an atom to form a negative ion.

When forming a negative ion, an atom undergoes the following reaction::

atom + electron (e^-) -> negative ion + energy

For example, consider the reaction by which chlorine forms a negative ion:

Cl + e^- -> Cl^- + 348 kJ / mole

This means that 348 kilojoules of energy are released when 1 mole of electrons is added to one mole of chlorine atoms. The following animation shows this electron affinity reaction of the chlorine atom:

Electron affinity tends to be high for nonmetals and low for metals. The general trend of electron affinity is to increase from left to right in any period and to decrease from top to bottom in a family of elements. For example, fluorine has a very high electron affinity. It is said to be very electronegative.