Se calculeaza nr.moli element ; ν=80 g / 40g/mol =2 mol
in 2 moli sunt 96,352x10²³ electroni s 144,528x10²³electroni p
in 1 mol 48,176x10²³ '" 72,264x10²³ ''''''
in 1 atom 8 electroni s 12electroni p prin impartirea numerelor cu numarul lui Avogadro, 6,023x10²³ electroni/mol
1s2 2s2 2p6 3s2 3p6 4s2 ->Z=20 element aflat inperioada 4, grupaII==>Ca