Rules for Writing Formulas for Ionic Compounds

Rules for Writing Formulas for Ionic Compounds

1.     Write the metal symbol first and then the non metal symbol second.

Ca                           I

2.     Write the cation charge above the metal and the anion charge above the non metal

2+                         1-

       Ca                     I

3.     Do the crossover rule and write the charge for the cation as a subscript for the non metal symbol and the charge for the anion as a subscript for the metal.

2+                         1-

                       Ca                    I     à CaI2     ß subscript goes at the                                                                                                                         bottom of the symbol

                                                                        and is smaller.

Rules for Naming Ionic Compounds

First Word – Name of the metal

Second Word – Name of the non-metal end in “ide”

Ex: Calcium Iodide

Rules for Naming Ionic Compounds with Transition Metals

The stock naming system uses roman numerals to indicate the charge of the cation because they can have more than one charge.

First Word – Name of the metal

Roman numeral in brackets to indicate the charge

Second Word – Name of the non-metal end in “ide”

Ex:              FeCl3 is Iron (III) chloride

                   FeO is Iron (II) oxide

                   Cu2S is coper (I) Sulfide

                   PbO2 is lead (IV) oxide

How do I know the charge for iron is 3? I use the reverse crossover rule

                                                3+               1-

Ex:              FeCl3 à                   Fe               Cl à   Iron (III)Cloride

Rules for Naming Ionic Compounds with Transition Metals

The stock naming system uses roman numerals to indicate the charge of the cation because they can have more than one charge.

First Word – Name of the metal

Roman numeral in brackets to indicate the charge

Second Word – Name of the non-metal end in “ide”

Ex:              FeCl3 is Iron (III) chloride

Rules for Naming Ionic Compounds with Transition Metals

The classic naming system uses the latin word with the ending “ous” to indicate the transition metal’s with the lower ion charge and the ending “ic” to indicate the greater ion charge of the transition metal.

For example: Fe is Ferrum and can have a charge of +2 ferrous or +3 ferric.

Element	Latin Name	Ion with lower charge		Ion with Higher Charge
Iron			Fe2+		Fe3+
Copper	Cuprum		Cu+		Cu2+
Lead	Plumbum		Pb2+		Pb4+

Formula	Classical System	Stock System
FeCl3	Ferric Chloride
FeO	Ferrous Oxide
Cu2S	Coprous Sulfide
PbO2	Plumbic Oxide

Write the chemical formula for each

a) Copper (I) Oxide

b) Lead (IV) Bromide

c) Iron (III) Sulfide

d) Nickel (III) Flouride

e) Manganese IV) Fluoride

Posted in: formulas,ionic compounds,naming compounds