# What is the mass of an atom that contains two positively charged nuclides, and two neutrally charged nuclides? What is the atom?

Atomic mass is to a very good first approx. NUCLEAR mass, i.e. the number of massive nuclear particles. The helium nucleus has 2 protons, 2 positively charged, massive particles, $Z = 2$, and this is what defines the nucleus as helium. The common helium isotope also contains 2 neutrons to give ""^4He. Capisce?