Al are Z=13 si A=27
23 23
27g-----------1mol Al-------------6,023.10 atomi----------------14.6.023.10 neutroni
81-----------------x-----------------y ----------------------------------a
x=81:27=3moli Al
23 23 23
y=81.6,023.10 :27=3.6,023 .10 atomi Al =18,069.10 atomi
nr.de neutroni=A-Z=27-13=14
23 23
a=81.14.6,023.10 :27=42.6,023 .10 neutroni