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Ionic Radii

cation size

anion size

Cations are smaller than their atoms, and anions are larger than their atoms.

Li	1.52	Be	1.11			N	0.75	O	0.73	F	0.71
Li¹⁺	0.60	Be²⁺	0.31			N^3–	1.71	O^2–	1.40	F^1–	1.36
Na	1.86	Mg	1.60	Al	1.43			S	1.04	Cl	0.99
Na¹⁺	0.95	Mg²⁺	0.65	Al³⁺	0.50			S^2–	1.84	Cl^1–	1.81
K	2.27	Ca	1.97					Se	1.17	Br	1.14
K¹⁺	1.33	Ca²⁺	0.99					Se^2–	1.98	Br^1–	1.95
Rb	2.48	Sr	2.15					Te	1.37	I	1.33
Rb¹⁺	1.48	Sr²⁺	1.13					Te^2–	2.21	I^1–	2.16

Atomic and Ionic Radii (Å) of Selected Main Group Elements