H are 1e iar O are 6e-( sunt electronii de pe ultimul strat)--> 1 molecula are in total 2x1+6=8e
1mol apa are M=18g ..... are N,A=6,023x10²³ molecule
18g.............8x6,023x10²³ e
27g............................x=72,27x10²³ e
N,A este numarul lui Avogadro