All helium atoms have 2 protons. what is the atomic number of helium?

All helium atoms have two protons, and no other elements have atoms with two protons. In the case of helium, the atomic number is 2. The atomic number of an element is usually written in front of and slightly below the element's symbol, like in the Figure below for helium.

neutrons are in the middle of the atom and the electrons, which are much smaller.