Atomic Radius Trend Guide
Search any element by symbol or name to see its atomic radius, periodic position, and how trends in size vary across periods and groups.
Element Lookup
Periodic Trends
Across a period (left → right): Radius decreases. More protons attract electrons more strongly without adding shells, shrinking the atom.
Down a group (top → bottom): Radius increases. Each period adds a new electron shell, pushing the outer electrons farther from the nucleus.
Largest atoms: Alkali metals (Group 1) in higher periods — Cs, Rb, K.
Smallest atoms: Noble gases and halogens in period 2 — He, F, Ne.
Down a group (top → bottom): Radius increases. Each period adds a new electron shell, pushing the outer electrons farther from the nucleus.
Largest atoms: Alkali metals (Group 1) in higher periods — Cs, Rb, K.
Smallest atoms: Noble gases and halogens in period 2 — He, F, Ne.