Ionic radii table

What is Ionic Radii ?

Ionic radii is related to ions present in ionic substances (crystalline solids). Ions are formed when neutral atom either gain or lose electrons. The effective size of the cation (+ charged) or anion (- charged) is termed as ionic radius. It is defined as the distance between the nucleus and outermost shell of an ion or it is the distance between the nucleus and the point where the nucleus exerts its influence over the electron cloud.

Comparative size of the atoms and the cations in the table

Comparison of the ionic radii with corresponding atomic radii of the cation is always smaller than the atomic radii of the parent atom. The radius of the anion is always larger than the atomic radii of the parent atom.

Comparative size of the atoms and the cations in the table

Atom	Atomic radii (crystal radius)Ao	Corresponding cation	Ionic radii (Ao)
Li	1.52	Li+	0.59
Na	1.86	Na+	0.99
K	2.31	K+	1.33
Mg	1.60	Mg2+	0.65
Ba	2.22	Ba2+	1.35
Al	1.43	AL3+	0.50
Pb	1.75	Pb2+	1.32

Comparison of atoms and their anions in the table

Atom	Atomic radii (crystal radius)Ao	Corresponding cation	Ionic radii (Ao)
F	0.72	F­-	1.36
Cl	0.99	Cl-	1,81
Br	1.14	Br-	1.96
O	0.73	O2-	1.04
S	1.04	S2-	1.84
N	0.75	N3-	1.71
P	1.10	P3-	2.12

The Z/e Ratio and comparison of different radii

In any particular group, the ions either anions or cations increases as we move top to down, this is because the increase in the number of shell as observed in case of the atomic radius. The size of the cation decreases with the increase in the positive charge. And the size of the anion increase as the negative charge on the anion increases.

This can be explained on the basis of Z/e ratio, whenever this ratio increases, the size of the ion decreases.

Na	Na+	Cl	Cl-	Fe2+	Fe3+
Z/e=11/11=1	11/10=1.1	17/17=1	17/18=.95	26/24=1.08	26/23=1.13

Therefore the relation between the ionic radii and the ions would be:

 Na>Na⁺    Cl <Cl^-   Fe²⁺>Fe³⁺