Atoms are the smallest unit of any chemical element that reacts in the same way as the whole element. Components: Protons - large, positively charged particles. Neutrons - large particles with no charge. Electrons - tiny, negatively charged particles. Protons and neutrons exist together in the nucleus of an atom, and are held together by extremely strong attractive forces. They form most of the mass of the atom. Electrons are so small and unpredictable that their location in an atom is never set; instead, they hover around the nucleus in an electron "cloud", or an area with 99% probability that the electron will be there. These electron clouds have distinctive shapes called orbitals.