Complex ions
A hydrated cation such as Zn(H2O)2+4 is an example of a complex ion. A complex ion consists of a central metal ion bonded to ligands.Ligands have a lone electron pair that is used in bonding to the central cation.
Anions (OH–, Cl–, or SCN–) or molecules (H2O or NH3) can be ligands. Factors such as size and charge affect the number of attached ligands, but 2, 4 and 6 are common.
Anions (OH–, Cl–, or SCN–) or molecules (H2O or NH3) can be ligands. Factors such as size and charge affect the number of attached ligands, but 2, 4 and 6 are common.
The overall charge on a complex ion is the sum of the charge of its central ion plus the sum of the charges (if any) on the attached ligands.
Zn(OH)2–4 from Zn2+ + 4OH– has a charge of +2 +(4 x –1) = –2
Zn(H2O)2+4 from Zn2+ + 4H2O has a charge of +2
Zn(H2O)2+4 from Zn2+ + 4H2O has a charge of +2
In aqueous solution, metal cations exist as hydrated complex ions such as Zn(H2O)2+4 which are often represented simply as Zn2+(aq).