ustaw liczby protonów i elektronów w atomach pierwiastków : magnezu , germanu , azotu , tlenu , węgla.

Mg p = 12 e = 12 n = 24 - 12 = 12 Ge p = 32 e = 32 n = 73 - 32 = 41 N p = 7 e = 7 n = 14 - 7 = 7 O p = 8 e = 8 n = 16 - 8 = 8 C p = 6 e = 6 n = 12 - 6 = 6