Compounds & Molecules Counting atoms

Counting atoms in a chemical fomula Add up the subscripts. Ca 3 P 2 = 5 atoms Don’t forget the “invisible” 1’s CaCO 3 = Ca 1 C 1 O 3 = 5 atoms Multiply anything inside parentheses by the subscript on the outside. Ba(NO 3 ) = 1 Ba, 2 N, 6 O = 9 atoms 22

Practice AlPO 4 MgC 2 O 4 Pb(MnO 4 ) 2 AgI Li 2 S B 2 (S 2 O 3 ) How Many Atoms?

Binary Compounds Writing Chemical Formulas

The metal (or + ion) is always written first. The nonmetal (or – ion) is always written last. The subscripts tell how many of each atom or polyatomic ion you have.

Writing Chemical Formulas EXAMPLE: Write the chemical formula for the ionic compound containing Al and Br. #1 – determine the charges Al +3 Br

Writing Chemical Formulas #2 – cross the charges. Do not carry the sign (+/-) and do not write the number 1. Al 3 Br 1 #3 – simplify if needed (lowest common factor) Not needed here

Writing Chemical Formulas You try: Mg and SMg 2 S 2 Simplify - MgS

Writing Chemical Formulas USING POLYATOMIC IONS Na and OH -1 Na +1 OH -1 NaOH Ca and PO 4 -3 Ca +2 PO 4 -3 Ca 3 PO 4 2 ???

Writing Chemical Formulas **If the polyatomic ion gets a subscript you MUST use parentheses.** Ca 3 (PO 4 ) 2

Naming Ionic Compounds With Main Group Metals 1.Name the + Ion – Name the metal. 2.Name the - Ion - Name the nonmetal, changing the ending to –ide

Naming Ionic Compounds Examples: MgO CaCl 2 magnesium oxide calcium chloride

Naming Ionic Compounds With Polyatomic Ions 1.Name the + ion or polyatomic ion 2.Name the – ion or polyatomic ion Examples: NaNO 3 Al 2 (SO 4 ) 3 sodium nitrate aluminum sulfate