1. Writing Chemical Formulas
Dr. Jerry E. Sipe
Ivy Tech Community College

2. Magnesium Chloride ide Mg+2 Cl-1 Mg Cl
Indicates this compound has only two elements – magnesium and chlorine
Mg+2
Cl-1
To write the formula “cross multiply” the charges Mg Cl 1 2

3. Calcium Phosphide ide Ca+2 P-3 Ca P
Indicates this compound has only two elements – calcium and phosphorous
Ca+2
P-3
To write the formula “cross multiply” the charges Ca P 3 2

4. Ammonium Sulfide Ammonium ide NH4+1 s-2 (NH4) NH4 S
Indicates a polyatomic ion, ammonium ion
Indicates this compound has a single element anion - sulfur
NH4+1
s-2
To write the formula “cross multiply” the charges
(NH4)
NH4 S 1 2

5. Sodium Sulfite Sodium Sulfite Na+1 SO3-2 Na SO3
Indicates this compound has a single element cation - sodium
Indicates a polyatomic ion consisting of S & the lowest level of oxygen possible
Na+1
SO3-2
To write the formula “cross multiply” the charges Na
SO3 2 1

6. Aluminum Bromide ide Al+3 Br-1 Al Br
Indicates this compound has only two elements – aluminum and bromine
Al+3
Br-1
To write the formula “cross multiply” the charges Al Br 3 1

7. Copper(II) Phosphate Copper(II) Phosphate Cu+2 PO4-3 Cu (PO4) PO4
Indicates this compound has a single element cation, copper, and its charge is +2
Indicates a polyatomic ion consisting of P & the highest level of oxygen possible
Cu+2
PO4-3
To write the formula “cross multiply” the charges Cu
(PO4)
PO4 3 2