• 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: N2O = (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- = Cl2

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) NaHCO3 (sodium hydrogen carbonate)

NaOH (Sodium Hydroxide)

(NH4)SO4 (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