Writing Formulas and Names for Ionic Compounds

I can write the name and formula for a binary ionic compound.

A binary ionic compound is a compound made up of two types of elements ( a metal and a non-metal)

Examples include sodium chloride (NaCl) and Iron (III) oxide (Fe2O3)

Ionic formulas show the ratio of positive ions to negative ions in the substance.

The ratio must be just right so that the total positive charge will balance the total negative charge. The sum of the charges must equal zero.

Writing Formulas

1. Look up the charge (oxidation number) of the cation and the anion.

2. If the sum of the charges is zero, write the symbol for the metal followed by the symbol for the nonmetal.

3. If the sum of the charges is not zero, use a subscript on either or both elements to balance the charge. Always write the symbol for the metal first.

Examples

Write the formula for magnesium chloride, aluminum oxide and sodium sulfide

MgCl2, Al2O3, Na2S

Writing Names, when given the formula

1. Write the name of the cation.

2. Write the name of the anion, but drop the standard ending and add “ide”.

Examples: Write the name of NaF, Ca3N2, K2S

Sodium fluoride, Calcium nitride, potassium sulfide

Writing formulas with transition metals, given the name.

1. The name will include a roman numeral. The Roman numeral is the charge on the cation.

2. Look up the charge on the anion.

3. If the sum of the charges is not zero, use subscripts on either or both elements to balance the charge.

Examples: Write the formula for Copper (II) oxide and Iron(III) Chloride

CuO, FeCl3

Writing names transition metals, when given the formula.

1. Write the name of the cation (transition metal)

2. You MUST use a Roman numeral that represents the charge in the name except-

A. Zinc, Cadmium- always use 2+

B. Silver- always use 1+

C. Scandium, Yttrium- always use 3+

3. For all other transition metals, use the charge on the anion(s) to determine the charge of the transition metal. The sum of the charges must equal zero!

4. Write the name of the anion, but drop the standard ending and add “ide”.

Ex: PbCl2, CuO Fe2O3

Lead (II) chloride, Copper (II) oxide Iron (III) oxide

Writing formulas with POLYATOMIC IONS

Polyatomic ion- a charged group of atoms that are chemically bonded together. OH -1 hydroxide

SO4 -2 sulfate

CO3 -2 carbonate

Use the charge on cation and anion to determine the subscript for each element or polyatomic ion. Sodium hydroxide

Aluminum sulfate

Potassium carbonate

If you need to add a subscript to a polyatomic ion, use a parenthesis, ex:

Magnesium hydroxide- Mg(OH)2

Writing names of compounds that contain polyatomic ions.

Write the name of the cation, usually the metal.

Exception- Ammonium- NH4 +1 is the only polyatomic cation

Write the name of the anion, usually the polyatomic ion.

Use the chart to find name and formulas for polyatomic ions.

Examples:

(NH4)2SO4

Al(OH)3

Cu(OH)2