text: how are the group number and the number of valence electrons of a representative element related to each other pls answer it right away!!!!! the number of electrons in the outermost  shell of an atom of an element , that is the valence shell electrons determines the group under which the element is placed.   since some atoms can have d same number of atoms in their outermost shell, it is only wise 2 place them under the same group. though the number of their electron shells vary.