All atoms must have protons in order to be called atoms. Protons are one of the three subatomic particles that make up an atom, the other two being neutrons and electrons. Protons are positively charged, while neutrons have no charge and electrons are negatively charged. The number of protons in an atom determines its atomic number, which identifies the element. For example, all atoms with one proton are hydrogen atoms, all atoms with two protons are helium atoms, and so on.