Composite: substance that can be broken down. Fundamental constituents: material that can"t be broken down. Compound - consists of two or more chemical elements (ex: h2o) Molecule - smallest unit of a compound, can be broken down into component elements, no longer have properties of the compound (ex: h, o) Element - fundamental unit of matter, cannot be broken down into simpler substances, but can be broken down to constituent atoms (ex: h, o) Atom - fundamental unit of an element, can only be broken down into subatomic. Subatomic particle - electrons, protons, neutrons; no longer have properties of particles parent atom. Electronically stable atoms have same number of protons as electrons. Periodic table: tabular arrangement of chemical elements ordered by atomic number, electron configuration, chemical properties. Hydrogen: max 2 electrons, 1 electron and 1 proton; oxygen: max 8 electrons, 8 electrons and 8 protons. Elements have a fixed atomic number, but varying atomic weight.