The structure of this Letter is as follows. After introducing exact two-particle electron wave function we redefine the covalency to extract from standard definition the contribution of atomicity, by referring to the notions of Mott and Hubbard localization. This new formulation allows us to define and determine explicitly the true covalency, atomicity (also termed seniority ), and ionicity factors in the chemical bond and hence to understand those component factors of the chemical bond in a fully quantita-tive manner. The whole methodology is based on combination of both the first-and secondquantization aspects of the relevant multielectron states, detailed in the Supporting Information.