Chemical Formulas Uses chemical symbols to represent the atoms of the elements and their ratios in a chemical compound Example: CO 2

Chemical Formulas CaF 2 Be(OH) 2 NO 2 Al 2 (SO 4 ) 3 Na 2 CO 3

IONIC BONDING Ion: an atom or group of atoms that has become electrically charged Atom loses electron = positive charge (cation) Atom gains electron = negative charge (anion)

Oxidation Numbers Used to keep track of how many electrons are lost or gained Example: Group 1; lose 1 electron = oxidation number is 1+ ( 1 more proton than electrons)

IONIC BONDING Ionic bond: the attraction between two oppositely charged ions (transfer of electrons) Usually between metals & nonmetals

IONIC BONDING Compounds are electrically neutral.  When ions come together, they balance out the charges on the ions  Group 1 & Group 17

IONIC BONDING Polyatomic ions: ions that are made of more than one atom “poly” means many A group of ions that react as one Each polyatomic ion has an overall positive or negative charge. Example: CO 3 (carbonate ion) has a charge of 2-. It can combine with a calcium ion Ca (2+) to form calcium carbonate.

NAMING IONIC COMPOUNDS Name of the positive ion comes first; followed by the name of the negative ion + ion is usually a metal If negative ion is an element--- end of its name is changed to “ide”

PROPERTIES OF IONIC COMPOUNDS Crystal shape Orderly, 3-D arrangement Held together by attraction between opposite charges High melting points Break bonds Electrical conductivity ONLY when dissolved in water; ions separate---move freely

COVALENT BONDING Electrons are shared, NOT transferred. Both atoms attract the shared electrons. Usually between 2 or more NONMETALS Examples: oxygen, carbon, nitrogen, & the halogens Frequently bond to other nonmetals

COVALENT BONDING Oxygen can form 2 covalent bonds….has 6 valence electrons; can share the other 2 Hydrogen can never have atoms with 8 electrons even when bonds. ONLY have 2 electrons & forms 1 bond

COVALENT BONDING Molecular compounds:  Molecules that have covalently bonded atoms  Molecules are held close together  Forces holding them are weaker than ionic compounds  Lower melting/boiling points than ionic compounds

COVALENT BONDING Molecular compounds:  Poor conductors of electricity No charged particles to move; electricity does not flow  Examples: plastic, rubber

COVALENT BONDING Nonpolar: equal sharing of electrons (CO 2 ) Polar: unequal sharing of electrons (H 2 O)  Some atoms pull more strongly than others