2. Atom: basic unit of matter Subatomic Particle ChargeLocation PROTONPositiveIn the nucleus NEUTRONNeutral (no charge) In the nucleus ELECTRONNegativeIn energy levels surrounding the nucleus

3. There is a unique atomic symbol that represents each ELEMENT (a pure substance consisting of one type of atom). The atomic number is the number of PROTONS. Atomic mass = PROTONS + NEUTRONS

4. Atoms with the same number of protons but different number of neutrons Have the same chemical properties because they have the same number of ELECTRONS Some are RADIOACTIVE and are unstable and breakdown over time Important uses Determine age of rocks & fossils Treat cancer Kill bacteria that causes food to spoil Used as labels or tracers to follow the movement of substances within organisms

5. Compound Substance formed by the chemical combination of two or more elements in definite proportions Represented by a chemical formula H 2 O, NaCl

6. Chemical Bonds Hold together atoms in compounds Involves the VALENCE ELECTRONS The electrons in the outer energy level available to form bonds Main types are ionic bonds and covalent bonds

7. Ionic Bonds Electrons are transferred from one atom to another Results in ions Positively and negatively charged atoms

8. Covalent Bonds Electrons are shared between atoms Results in a molecule The smallest unit of most compounds