Question

Define electron affinity. What is its unit?

Answer 1

Electron affinity:

Another important property that determines the chemical properties of an element is the tendency to gain an additional electron.

The amount of energy released when an electron is added to a neutral atom to form an anion is called electron affinity.

• It corresponds to the process : $\mathrm{X}\left(\mathrm{g}\right)+{\mathrm{e}}^{-}\to {\mathrm{X}}^{-}\left(\mathrm{g}\right)+\mathrm{E}$, here, X is an atom of an element.
• Electron affinity increases going left to right across a period because of increased nuclear charge.
  Going down the group the electron affinity should decrease since the electron is being added increasingly further away from the nucleus. Electron becomes less tightly bound and can be easily removed
• The energy change is measured in the unit kJ mol^-1.