The other subatomic particles that make up a magnesium atom besides protons and electrons are neutrons. Protons are positively charged, electrons are negatively charged, and neutrons have no charge. The nucleus of a magnesium atom contains 12 protons and 12 neutrons, while the electron cloud contains 12 electrons. The number of protons in an atom determines what element it is, so all magnesium atoms have 12 protons. The number of neutrons can vary, however, giving rise to different isotopes of the same element. Magnesium has three stable isotopes: magnesium-24, magnesium-25, and magnesium-26. The three isotopes of magnesium have 12, 13, and 14 neutrons, respectively.