1 mol Na ........................23gNa...............6,023·10²³ atomi
57,5gNa ...............x
x = 57,5x 6,023·10²³/23
x = 15,0575· 10²³ atomi Na
Nr. neutroni ai unui atom ; A-Z = 23-11
= 12n⁰
1 atom Na .............................12n⁰
15,0575·10²³atomi ....................y
y = 15,0575·10²³ x 12
y = 180,69 · 10²³ n⁰ (neutroni)