Combined elements –Compounds = unique properties from the elements that make them up. –NaCl for example Na = shiny, soft, silvery, metal that reacts violently with water Cl = a poisonous greenish yellow gas NaCl = table salt Chapter 5

Formulas Chemical formula = tells what elements a compound contains and the exact number of atoms of each element in a unit of that compound. Example: N 2 O = (2 nitrogen atoms 1 oxygen atom)

Atomic Stability Why do atoms form compounds? –The electric forces between electrons and protons (opposites) cause compounds to form

Atomic Stability An atom is chemically stable when its outermost energy level has the maximum number of electrons. For H and He …2 electrons equal stable For all other elements…8 electrons = stable

How do outer levels get their fill? Atoms with partially stable outer energy levels can lose, gain, or share electrons to obtain stable outer energy levels Ion = an charged particle because it has more or less electrons than protons They do this by combining with other atoms

Chemical Bond Chemical bond = the force that holds atoms together in a compound The force occurs when atoms gain, lose, or share electrons…an attraction forms that pulls the atoms together to from a compound

What holds bonded atoms together? –When their valence electrons interact (outer most shell) –Atoms join so that each atom has a full outermost energy level

Ionic Bonds Formed by the transfer of electrons Ex) Na+ bonds w/ Cl - = NaCl Each atom loses or gains electrons Metals bond with nonmetals Melting point = high Ionic bonds tend to conduct electricity

Ionic Bond

Covalent Bonds Bond formed when elements share one or more electrons. Ex) Cl - bonds with a Cl - = Cl 2 EX) C +2 bonds w/ O -2 = CO (carbon monoxide) Nonmetals combine with nonmetals Melting point = low

Ionic and Covalent Bond Video

Polyatomic Ions Can have both ionic and covalent bonds Usually groups of covalently bonded atoms that have lost or gained electrons Ex) NaHCO 3 (sodium hydrogen carbonate) NaOH (Sodium Hydroxide) (NH 4 )SO 4 (ammonium sulfate)

Metallic Bonds Bond formed by the attraction between positively charged metal ions Electrons move freely from metal atom to metal atom This is why metals conduct electricity so well