How is the number of valence electronsfor a neutral atom calculated?

The number of valence electrons in a neutral atom is determined by its position in the Periodic Table. Specifically, for main group elements (groups 1, 2, and 13-18), the number of valence electrons corresponds to the group number. For example, elements in group 1 have one valence electron, while those in group 17 have seven. Transition metals and inner transition metals have more complex electron configurations, but their valence electrons can generally be inferred from their electron configurations as well.