What are atoms? Atoms are the basic building blocks of matter in physics. They are made up of three types of particles: protons, neutrons, and electrons. Proton is a positively charged particle located in the nucleus, or center of an atom. Neutrons are neutral, meaning they have no charge and are also found in the nucleus. Electrons are negatively charged particles that revolve around the nucleus in a shell or energy level. The number of protons in an atom's nucleus is called the atomic number, which determines to which element the atom belongs. For example, all atoms with 6 protons in their nucleus are carbon atoms. The number of neutrons and electrons can vary in a particular element, resulting in different isotopes of that element. An atom's electrons are responsible for chemical reactions and bonding with other atoms. The number of electrons in the outermost shell of an atom, also known as the valence shell, determines its reactivity. Atoms with complete valence shells ten...