How many protons and neutrons are there in Aluminium?

The atomic number, Z of aluminium, Al is 13. Hence there are 13 protons. Note: Atomic number, Z represents the number of protons in a given atom. Number of neutrons depends on the isotopic form of aluminium. More than 99.9% of naturally occurring aluminium is 13Al27. Where 27 is the mass number, A; and 13 is atomic number, Z. Now, Mass number, A = no. of protons + no. of neutrons. or A = Z + no. of neutrons. Therefore, the number of neutrons in above isotope = A - Z = 27 - 13 = 14. Note: The molar mass of aluminium, which is average of atomic masses of all isotopes = 26.981538 g/mol, since 13Al27 is the major isotope.