The one valence electron leaves sodium and adds to the seven valence electrons of chlorine to form the ionic formula unit NaCl ( ). For instance, the four valence electrons of carbon overlap with electrons from four hydrogen atoms to form CH 4.

Remember that in most main group element compounds, the valence electrons of the isolated atoms combine to form chemical bonds that satisfy the octet rule. This figure shows, from left to right, solutions containing n+ ions with M = Sc 3+( d 0), Cr 3+( d 3), Co 2+( d 7), Ni 2+( d 8), Cu 2+( d 9), and Zn 2+( d 10). Metal ions that contain partially filled d subshell usually form colored complex ions ions with empty d subshell ( d 0) or with filled d subshells ( d 10) usually form colorless complexes.