# Using this model of a helium atom, what is the atomic number and mass number?

Using the standard model of the helium atom, $Z = 2$; that is there are 2 protons, 2 massive positively charged particles in the helium nucleus, and $Z = \text{the atomic number} = 2$. Because helium is a NEUTRAL entity (most matter is!), associated with the atom there are 2 electrons, conceived to whizz about the nucleus. Also contained in the helium nucleus, there are 2 neutrally charged $\text{neutrons}$, which are massive particles of neutral charge. And thus we represent the helium atom as ""^4He. Why don't we have to specify the $\text{atomic number}$ in this label?