Hence atomic number = 18 Number of protons + neutrons = 18 + 22 = 40. Hence mass number = 40The chemical ... first shell and one in the second shell. Sodium has 11 electrons.

All oxygen atoms have 8 protons and all sodium atoms have 11 protons ... out the number of neutrons by subtracting the atomic number from the mass number. In this example, it is 35 – 17 ...