1. Section 3: Writing Formulas and Naming Compounds
Chapter 20: Chemical Bonds
Section 3: Writing Formulas and Naming Compounds

2. Binary ionic compounds
Binary compound- one that is composed of 2 elements
Example: KI, NaCl
But before you can write these we have to know a few pieces of information…

3. What will I need to know to write an ionic formula?
Are electrons gained or lost?
When you know this…you can figure out the oxidation number- tells you how many electrons an atom has gained, lost, or shared to become stable (IT’S THE CHARGE)
Example: Na has an oxidation # of +1
When something looks like this: iron(III) oxide, the roman numeral is the oxidation number of iron
But…compounds are neutral
Example: CaF2 and Al2O3

4. Oxidation numbers

5. Writing Ionic formulas
1. Always write the positive ion first (metal) followed by the negative ion (nonmetal)
2. (Hint) The charge of one ion (without the sign) becomes the subscript of the other ion
Example: You choose

6. Writing names of ionic compounds
1. Write the name of the positive ion
2. Use table 2 in your book to see if the positive ion is capable of forming more than one oxidation number. If so, determine the charge it is using by looking at the negative ion (only have 1 possible charge)
3. Write the root name of the negative ion
Example: Chlor- for chlorine and ox- for oxygen
4. Add the ending –ide to the root
Example: Tell me the name of BaF2

7. Compounds with complex ions
Not all compounds are binary
Example: NaHCO3
Contains a polyatomic ion- a positively or negatively charged, covalently bonded group of atoms
Table of these on p. 619

8. Common polyatomic ions

9. Writing names and formulas for compounds with complex ions
1. Write the name of the positive ion
2. Use Table 4 p.619 to find the name of the polyatomic ion
3. Write the name of the negative ion
Examples: K2SO4 and Sr(OH)2
Writing Formulas
Follow the rules for binary compounds, except when more than one polyatomic ion is needed, write parentheses around the polyatomic ion before adding the subscript
Example: Barium chlorate

10. Compounds with added Water
Some ionic compounds have water molecules as part of their structure
Called hydrates- a compound that has water chemically attached to its ions and written into its chemical formula
Naming
Example: CaSO4 2 H2O

11. Naming Binary Covalent Compounds
Remember, covalent compounds are formed between elements that are nonmetals
Using Prefixes
We use prefixes to
indicate the number
of atoms of each
element are in the
Compound
Example: N2O5