Representative elements have predictable charges.

Stock System

• Most transition metals and large p block metals have variable charge

• Roman numeral used to indicate the charge of the cation

• Exceptions to stock system (do not use the roman numeral): Groups 1 & 2, Ag⁺¹, Zn⁺², Cd⁺², Al⁺³

Cation charge from chemical formula

• Anions: get the charge from periodic table or charge of polyatomic anion.

• Get total (-) charge by multiplying subscript by charge.

• Total (-) charge = Total (+) charge

• Divide (+) charge by cation subscript

• Roman numeral is the charge of ONE cation.

Cation charge from chemical formula

• Anions: get the charge from periodic table or charge of polyatomic anion.

• Get total (-) charge by multiplying subscript by charge.

• Total (-) charge = Total (+) charge

• Divide (+) charge by cation subscript

• Roman numeral is the charge of ONE cation.