The subatomic particles found in the nucleus of an atom are protons and neutrons. Protons carry a positive charge, while neutrons are electrically neutral. The number of protons defines the element and is known as the atomic number. Together, protons and neutrons account for most of an atom's mass. Electrons, which are negatively charged and orbit the nucleus, are also important but are not located within the nucleus itself. The interactions between these subatomic particles govern chemical properties and behavior of elements.