defination of complexion, Ligand,co-ordination number, co-ordination sphere

complex ion : when a compound(say CuSO₄) is treated with an excess of another compund say (NH4OH) then a complex is formed which when dissolved in aqueos solution may not give  positive test for all of the ions involved in the complex.

ligand : neutral or negatively charged species that donates a lone pair of electron the vacant d or f orbitals of mtal atoms.

co-ordination number : its the no. of co ordinate complex bonds formed between entral metal atom and the ligand.

co-ordination sphere: its the representation of the central metal atom surrounded by the ligands enclosed in a square bracket.