Yes, all atoms that have the same number of protons belong to the same element. The number of protons in an atom is called the atomic number, and it is what defines the element. For example, all atoms with one proton are hydrogen atoms, all atoms with two protons are helium atoms, and so on.

The number of neutrons in an atom can vary, and this gives rise to different isotopes of an element. Isotopes have the same number of protons and electrons, but they have different numbers of neutrons. For example, there are three naturally occurring isotopes of hydrogen: protium, deuterium, and tritium. Protium has one proton and no neutrons, deuterium has one proton and one neutron, and tritium has one proton and two neutrons.