The atomic radii of metals are usually

Analyze the question: It asks how the atomic radius of a metal compares with its ionic radius, and also (in option D) how it compares with non-metals in the same period.

Concept:

• Metals usually form positive ions (cations) by losing electrons.
• When a metal atom loses its valence electrons, it often loses its whole outermost shell. The same nuclear charge now pulls fewer electrons, so the electron cloud shrinks.
• So a metal cation is smaller than its parent atom.

Example: Na (atomic radius ≈ 0.186 nm) → Na⁺ (ionic radius ≈ 0.095 nm) Na: 2,8,1 → Na⁺: 2,8 (one shell lost, and the 11 protons now hold 10 electrons).

Checking the options:

• A. Greater than their ionic radii: True. Atom → cation means the radius decreases.
• B. Equal: False. Losing electrons changes the size.
• C. Less than their ionic radii: False. This is true for non-metals, whose anions are larger than their atoms (Cl 0.099 nm → Cl⁻ 0.181 nm).
• D. Less than those of non-metals in the same period: False. Across a period, atomic radius decreases from left to right because nuclear charge increases. Metals are on the left, so they usually have larger atomic radii than the non-metals in the same period.

Answer: A

Exam tip: Remember "Cations are smaller, anions are bigger." Metals form cations, so their atoms are bigger than their ions. Non-metals form anions, so their atoms are smaller than their ions.