Aₓ=40 => x=Ca
40g Ca............x electroni s.........y electroni p
80g Ca...........96,352×10^23 electroni s..............144,528×10 la 23 electroni p
=>x=48.176 x10^23electroni s ; y=72.264 x10^23 electroni p (in 40 g Ca, adica intr-un mol)
=> nr electroni s dintr-un atom = 48.176x10^23/6.022x10^23=8
nr electroni p dintr-un atom= 72.264 x10^23/6.022x10^23=12
=>Ca : 1s²2s²2p⁶3s²3p64s²
Pozitie in tabelul periodic->grupa a 2-a A si perioada 4