Electron affinity

Definition

Electron affinity is the energy change that occurs when an electron is added to a neutral atom in the gaseous state. It measures the tendency of an atom to accept an electron.

5 Must Know Facts For Your Next Test

1. Electron affinity generally increases across a period from left to right due to increasing nuclear charge.
2. Electron affinity generally decreases down a group as atomic size increases and electron shielding effects become more significant.
3. Elements with high electron affinities often form negative ions easily, such as halogens.
4. The first electron affinity is typically exothermic (releases energy), while second or subsequent affinities are usually endothermic (require energy).
5. Noble gases have very low or positive electron affinities because they already possess stable electronic configurations.

Review Questions

• How does electron affinity change across a period on the periodic table?
• Why do elements in Group 17 (halogens) have high electron affinities?
• Explain why noble gases have low or positive electron affinities.

Related terms

Ionization Energy: The energy required to remove an electron from a neutral atom in its gaseous state.

Electronegativity: A measure of the ability of an atom in a molecule to attract electrons to itself.

Atomic Radius: The distance from the nucleus of an atom to the outermost shell of electrons.