1. Chemical Formulas Ex) NH3 Formulas express the types and numbers of
atoms in a compound
Symbols are used to represent the types of
elements
Subscripts are used to represent the number of atoms of each element
Ex) NH3

2. Ionic Compounds Ionic Compound – a compound composed of
cations and anions
Reminders:
Cation – positively charged ion
Anion – negatively charged ion
Overall charge of the compound is ZERO!

3. Ionic Compounds
Binary ionic compound – an ionic compound composed of two ions
metal ion + non–metal ion
Metals form monatomic cations
Nonmetals form monatomic anions

4. Writing Ionic Formulas
Determine the charges of the ions in the formula.
Write ions with charges.
Cations MUST be written first.
Cross and drop charges.
Use the absolute value of each ion’s charge as the subscript for the other ion. NO positive or negative sign.
Reduce subscripts to the lowest whole number ratio.

5. Writing Ionic Formulas
Ex) Write the formula for Magnesium Chloride
Step 1: Find the charges
Step 2: Mg2+ Cl–1
Step 3: MgCl2

6. Li1+ Cl-1 Ca2+ Br-1 Be2+ S-2 Al3+ O-2 More Examples Lithium chloride
Calcium bromide
Ca2+ Br-1
Beryllium sulfide
Be2+ S-2
Aluminum oxide
Al3+ O-2
LiCl
CaBr2
Be S = BeS
2 2
Al2O3

7. Naming Cations & Anions
Cation naming pattern
metal’s name
Ex) K+1 = potassium
Anion naming pattern
nonmetal’s stem + -ide
Ex) F–1 =fluoride

8. Naming Binary Ionic Compounds
Binary ionic compound naming pattern
metal’s name + nonmetal’s stem + -ide
Ex) KF = potassium fluor ide

9. More Examples NaCl Sodium chloride Li2O Mg3N2 Lithium oxide
Magnesium nitride