To find the average atomic mass, you take a certain number of atoms, find the total mass of each isotope, and then divide the total mass of all the atoms by the total number of atoms. Assume that you have, say, 10 000 atoms of carbon
Explanation:
atomic mass = 39
number of neutrons = 20
number of protons= 19
electronic configuration = 1s2 2s2 2p6 3s2 3p6 4s1
the number of electron in first shell = 2
number of electrons in n=3 shell = 8