Atoms are the smallest particle into which an element can be divided. The ancient Greek philosophers developed the concept of the atom, although they considered it the fundamental particle that could not be broken down. Subatomic particles were discovered during the 1800s. For our purposes we will concentrate only on three of them. The neutron has no charge, and a mass of slightly over 1 amu.
Some scientists propose the neutron is made up of a proton and electron-like particle.
The electron is a very small particle located outside the nucleus. Because they move at speeds near the speed of light the precise location of electrons is hard to pin down. Electrons occupy orbitals, or areas where they have a high statistical probability of occurring. The charge on an electron is -1. The atomic number is the number of protons an atom has.