Size periodic table trend

Atomic radius generally decreases across a period and increases down a group. These trends reflect changes in nuclear attraction, shielding, and occupied electron shells. Atomic radius is not one uniquely defined hard boundary around an atom.

Meaning and context

Across a period, the increasing nuclear charge generally draws the electrons more strongly while they occupy the same principal shell. Down a group, additional occupied shells usually increase the atom’s extent despite the larger nuclear charge.

Examples and usage

Different radius definitions, such as covalent and metallic radius, use different measurement contexts. Compare like with like in a data table. A value for an ion is also not automatically the radius of the neutral atom.

What to check

Trends help explain patterns but do not replace numerical data or remove every exception. Identify the species, charge, and radius definition before making a precise size comparison. Electron clouds do not have a sharp surface like a solid ball.

Explore more: Chemistry and Elements