Electron: A subatomic particle that has a negative charge.
Nucleus: An atoms central region, which is made up of protons and neutrons.
Proton: A subatomic particle that has a positive charge and that is located in the nucleus of the atom.
Neutron: A subatomic particle that has no charge and that is located in the nucleus of the atom.
Atomic Number: The number of protons in the nucleus of an atom.
Mass Number: The sum of the numbers of protons and neutrons in the nucleus of an atom.
Isotope: An atom that has the same number of protons as other atoms of the same element do, but has a different number of neutrons.
Unified Atomic Mass Unit: A unit of mass that describes the mass of an atom or molecule; it is exactly 1/12 the mass of a carbon atom with a mass number 12.
Mole: The SI unit used to measure the amount of a substance whose number of particles is the same amount as the number of atoms of carbon in exactly 12.g of carbon-12.
Orbital: A region in an atom where there is a high possibility of finding electrons.
Valance electrons: An electron that is found in the outermost shell of an atom and that determines the atoms chemical properties.