* Definition of a Hydrogen Atom: A hydrogen atom is defined by having one proton in its nucleus. That's what makes it hydrogen.
* Atomic Number: The atomic number of an element defines the number of protons in its nucleus. Hydrogen has an atomic number of 1, meaning it *must* have one proton.
* Isotopes: While hydrogen has isotopes (like deuterium with one proton and one neutron), they still maintain the same number of protons, just a varying number of neutrons.
If a hydrogen atom had 2 protons, it would no longer be hydrogen. It would become helium, which has an atomic number of 2.
