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

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

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

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

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

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

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