1. Tech Notes: Why Atoms Combine  Molecule and Compound:  Two or more atoms chemically combined  Have completely different properties than those of the elements  EXAMPLES:  Copper sulfate  Sodium chloride  Water

2. Chemical Formula  A combination of the symbols of the elements that produce the compound  Tells what elements the compound contain  Tells the ratio of the atoms:  Water: H 2 O  2 hydrogen : 1 oxygen  Sugar: C 12 H 22 O 11  12 carbon : 22 hydrogen : 11 oxygen

3. Electrons and Chemical Bonding  Chemical bonding: the combining of atoms to form molecules or ionic compounds  Valence electrons: electron in the outermost energy level of an atom.  Chemically stable: outer energy level completely filled with electrons  Ionic Bond: a bond that forms when one atom loses an electron and one atom gains an electron  Covalent bond: a bond formed when atoms share electrons

4. Electrons and Chemical Bonding  Three ways for bonds to form:  Atom loses an electron  Atom gains an electron  Atoms share electrons