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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Atomic radius

A measure of an atom's size, usually half the distance between the nuclei of two bonded identical atoms. It decreases across a period (rising ZeffZ_{\text{eff}}, same shell) and increases down a group (larger valence shell).

Periodic trend: increases down and to the leftMain-group block of the periodic table shaded from light to dark. The property (atomic radius, metallic character) increases down a group and from right to left across a period, so it is largest at the bottom left.← increases right to leftincreasesdown a groupperiod 2period 6darker = larger (atomic radius, metallic character)main groups only; noble gases aside

Radius grows down a group and toward the left of a period.

Example

K (227 pm) > Na (186 pm) > Cl (99 pm): K has one more shell than Na, and Cl has the same shell as Na but 6 more protons pulling on it.

See alsoIonic radiusEffective nuclear chargePeriodGroup