The presence of valence electrons can determine the element's chemical properties and whether it may bond with other elements: For a main group element, a valence electron can only be in the outermost electron shell.In a transition metal, a valence electron can also be in an inner shell.he most reactive kind of nonmetal element is a halogen (e.g., fluorine (F) or chlorine (Cl)). Such an atom has the following electron configuration: s 2 p 5; this requires only one additional valence electron to form a closed shell.