What do you mean by Electron affinity ? How it varies in group and periods in modern periodic table?

Explanation

The tendency of an element is to gain an additional electron. This ability is measured by electron affinity. It is the energy change when an electron is accepted by an atom in the gaseous state. Electron affinity is asigned positive value when energy is released during the process. Greater the value of electron affinity, more energy is released during the process and greater is the tendency of the atom to gain electron
In a group, the electron affinity decreases on moving from top to bottom as less and less amount of energy is released.
In a period, the electron affinity increases from left to right as more and more amount of energy is released