# What do electron affinity values mean?

Mar 8, 2016

Electron affinity by definition is the amount of energy released when an atom attracts an electron.

#### Explanation:

Electron affinity by definition is the amount of energy released when an atom attracts an electron.

Since this is a released energy, it is a negative entity. This applies only to first electron affinity, however, the second electron affinity is not necessary a released energy, most of the times for an atom to attract a second electron, it requires energy and therefore, it is a positive entity.

For example, the first electron affinity of oxygen to form ${O}^{-}$ is equal to $- 142 \frac{k J}{m o l}$ and the second electron affinity of oxygen to form ${O}^{2 -}$ is equal to $+ 844 \frac{k J}{m o l}$.

The second electron affinity requires energy due to:

1. The decrease in the electron to proton ratio (lower effective nuclear charge).
2. The electron electron repulsion in the same orbital, which is present for the first electron affinity but it is less effective since the effective nuclear charge was more important.