# Periodic Trends in Ionic Size

## Key Questions

• An ion's size, compared to its parent atom, depends on whether it gains or loses electrons.

Gaining electrons increases the apparent diameter, while losing electrons makes the ion smaller than the neutral atom.

For example if Na loses one electron to form $N {a}^{+}$, the latter is smaller than the Na atom.

When O gains two electrons to form ${O}^{2 -}$ the resulting ion is larger.