VI.
consideram ca X = x e-, Y = y e- si T = t e-
Daca sunt consecutive atunci
y =x+1, t=x+2
=> x +x+1+x+2 =21
=>x=6, y= 7 si t = 8
X: 1s2 2s2 2p2
Y: 1s2 2s2 2p3
T: 1s2 2s2 2p4
VII.
V.cub = L.la3 = 1la3 = 1 cm3
ro = m/V
=> m.Fe = ro×V
= 7,8×1 = 7,8 g Fe
1 mol Fe ......56 g Fe .....6,022×10la23 atomi Fe
7,8g Fe ..... n = 8,38×10la22 atomi Fe