Chapter 20 Section 3

Writing formulas and naming compounds The name and the formula give you information about the compound. Binary compound—a compound composed of two elements Ex: NaCl MgO2 FeO3 HCl Oxidation number—a superscript that tells you how many e- an atom has gained, lost, or shared to become stable.

Writing formulas Write the + ion first and it’s oxidation # Write the – ion second and it’s oxidation # Ex Li2+ N3- Crisscross the charges with out the sign to become the subscript of the opposite element. Ex: Li3N1

Variable oxidation #--some transition elements have more than one oxidation # These are shown with Roman numerals in parentheses.

Naming Ionic compounds First you say or write the name of the first element. Then you say or write the name of the second element and add –ide to the end Element -ide name Oxygen oxide Phosphorus phosphide Nitrogen nitride Sulfur sulfide

Name the following ionic compounds NaCl KI BaO Sodium Chloride Potassium Iodide Barium Oxide

Polyatomic ions A positively or negatively charged, covalently bonded group of atoms. When writing formulas with polyatomic ions, you say the name of the ion group and use the correct oxidation #. If there is more than one polyatomic, put the ion group in parentheses. Ex: Sr(OH)2 (NH4)3PO4 Ba(ClO3)2

Greek prefixes Used to indicate how many atoms of each element are in a binary covalent bond. (REMEMBER!! THESE ARE 2 NONMETALS) When naming compounds, don’t say two vowels together

# of atoms Prefix 1 Mono- 2 Di- 3 Tri- 4 Tetra- 5 Penta- 6 Hexa- 7 Hepta- 8 Octa- 9 Nona- 10 Deca-

Name the following compounds: PCl3 NO NO2 N2O5 ClO7

Hydrates A hydrate is a compound that has water chemically attached to its ions CoCl2 • 2 H2O