Chelation is the process of formation of chelates. The chemistry of chelation deals mostly with the interaction of electrons in the five d orbitals with the ligand field. The inert gases show no chemical activity and this is explained in terms of their electronic configuration or distribution of electrons in their various orbitals around the nucleus. According to the classical theory of valency, an atom combined with another atom or entered into a bond in order to achieve an inert gas electronic structure for each of the atoms. The binding of the metal atom to the ligands may be electrostatic or covalent in nature, with electron-pair bonds being most dominant. Metal complexes are compounds in which the metal atom is linked by more bonds than usually expected by valency considerations. The total number of ligand atoms bound directly to the central metal atom gives the coordination number of that metal.