Simple Substitution

Substitution in which the cations or anions replacing one another have the same charge and similar radii (within ~15%). Simple substitutions may result in complete or partial solid solution. The following simple substitutions are commonly complete: Fe2+ (0.78 Å) ↔ Mg2+ (0.72 Å), Fe2+ (0.78 Å) ↔ Mn2+ (0.83 Å), and Br- (1.96 Å) ↔ Cl- (1.81 Å). In contrast, the following substitutions are usually partial because they significantly differ in ionic size: Na+ (1.18 Å) ↔ K+ (1.51 Å), Mg2+ (0.72 Å) ↔ Mn2+ (0.83 Å), I- (2.20 Å) ↔ Cl- (1.81 Å).