1. Chapter 20
Section 3

2. 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.

3. 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

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

5. 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

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

7. 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

8. 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

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

10. Name the following compounds:
PCl3 NO
NO2
N2O5
ClO7

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