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,

Lead (II) chloride,
CuO
Copper (II) oxide
Fe2O3
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.
If you need to add a subscript to a
 Sodium hydroxide
polyatomic ion, use a parenthesis, ex:
 Aluminum sulfate

Potassium carbonate
Magnesium hydroxide- Mg(OH)2
Writing names of compounds that
contain polyatomic ions.

Write the name of the cation, usually the metal.


Write the name of the anion, usually the polyatomic ion.


Exception- Ammonium- NH4 +1 is the only polyatomic cation
Use the chart to find name and formulas for polyatomic ions.
Examples:

(NH4)2SO4

Al(OH)3

Cu(OH)2