Ionization energy

Definition

Ionization energy is the amount of energy required to remove an electron from a gaseous atom or ion. It is a key property that influences an element's reactivity and chemical behavior.

5 Must Know Facts For Your Next Test

1. Ionization energy generally increases across a period from left to right due to increasing nuclear charge.
2. Ionization energy decreases down a group because electrons are farther from the nucleus and experience more shielding.
3. Elements with high ionization energies tend to be nonmetals, particularly noble gases which have very stable electron configurations.
4. The first ionization energy refers to the energy required to remove the first electron, while subsequent ionizations require significantly more energy.
5. Anomalies in ionization energy trends can occur due to subshell configurations, such as between Group 2 and Group 13 elements.

Review Questions

• Why does ionization energy generally increase across a period?
• What is the difference between first ionization energy and second ionization energy?
• How does electron shielding affect ionization energy down a group?

Related terms

Electron Affinity:

The amount of energy released when an electron is added to a neutral atom in the gaseous state.

Electronegativity:

A measure of an atom's ability to attract and bind with electrons in a chemical bond.

Atomic Radius:

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