7. a) notam cu p+ = protonii si cu n0 = neutronii
Pb (Z = 82 si A = 207)
A = Z + n0 => n0 = A - Z = 207-82 = 125
=> 82p+ si 125n0
1 mol-atom Pb .... 82x6,0225x10la23 p+
4 ........................................... a = 4x82x6,0225x10la23
=> a = 1,975x10la20 p+
1 mol-atom Pb .... 125x6,0225x10la23 n0
4 ........................................... b = 4x125x6,0225x10la23
=> b = 3,011x10la20 n0
b).
Ag (Z = 47 si A = 108)
A = Z + n0 => n0 = A - Z = 108-47 = 61
=> 47p+ si 61n0
1 mol-atom Ag .... 47x6,0225x10la23 p+
5 ........................................... a = 5x47x6,0225x10la23
=> a = 1,415x10la20 p+
1 mol-atom Ag .......61x6,0225x10la23 n0
5 ........................................... b = 5x61x6,0225x10la23
=> b = 1,837x10la20 n0
