Quantum chemical definition and calculation of valence

A new quantum chemical definition of atomic valence is proposed by taking into account both the final and initial states of atoms forming molecules. For the practical calculation, we present a corresponding concrete calculation procedure within the framework of the maximum overlap population principle, which is very simple and very easy to perform. The calculated numerical results are in good agreement with chemists' intuitive concept of chemical bonding. For example, the valences of atoms H, C, N, O and F in all the analysed stable molecules are always close to 1, 4, 3, 2 and 1, respectively, which may be very useful in investigations of molecular structures.