Year 8 – The periodic table KEY WORDS Atom The smallest particle of material that can exist on its own. Nucleus The centre of an atom Electron A tiny negative particle whizzing around the outside of the nucleus of an atom Proton A positive particle found in the nucleus of an atom Neutron A particle with no charge found in the nucleus of an atom Element A substance made from one type of atom. Compound A substance made from 2 or more elements that have reacted together. Mixture A mixture of two or more elements or compounds that have not reacted together. Molecule A particle made from a small group of atoms joined together. Periodic Table A list of all known elements listed together. Reaction When two or more substances react bringing about a chemical change. Formula Shows what elements make up a substance. Equation Shows how chemicals react with each other in a reaction. Pure A material made only from one substance. The substance could be an element or a compound. Conservation of mass The idea that the mass of reactants in a chemical reaction will be equal to the mass of product. In other words no atoms can be lost or gained during a reaction. the horizontal rows are called periods the vertical columns are called groups An Atom