Valorile electronilor le împarți la nr. lui Avogadro
192,704*10^23 / 6,022*10^23 = 32 electroni s
289,056*10^23 / 6,022*10^23 = 48 electroni p
40 g element E........x electroni s.........y electroni p
160 g element E.........32 electroni s.........48 electroni p
x = 8 electroni s
y = 12 electroni p
1s2 2s2 2p6 3s2 3p6 4s2 - Z = 20 - calciu