Science 1206 – Writing formulas of Ionic compounds worksheet
Examples:
1.
Write the formula for Magnesium Bromide
Solution:
Step 1: Identify the elements in the compound
Magnesium  Mg
Bromide  Br
Step 2: Identify the charge on each ion
Mg  2+
Br  1-
Step 3: The charge of one ion tells us the number of the other ion present in the
formula (criss cross method).
Mg has a 2+ charge so there are 2 Br ions. Br has a 1- charge so there is
only 1 Mg ion.
Step 4: Write the formula, with the metal first, and the non-metal last.
MgBr2
2.
Write the formula for Calcium Phosphate
Solution:
3.
4.
Step 1:
Calcium  Ca
Phosphate  PO4
Step 2:
Ca  2+
Phosphate  3-
Step 3:
There are 3 Ca2+ ions and 2 PO43- ions (criss cross)
Step 4:
Ca3(PO4)2
Write the formula for Chromium(III) Sulfide
Step 1:
Chromium(III)  Cr
Step 2:
Cr(III)
Step 3:
There are 2 Cr3+ ions and 3 S2- ions
Step 4:
Cr(III)2S3
 3+
Sulfide  S
Sulfide  2-
Write the formula for Copper(I)Fluoride Trihydrate
Step 1:
Copper(I)  Cu
Step 2:
Cu(I)
Step 3:
There is 1 Cu1+ ion and 1 F1- ion
Step 4:
CuF
Step 5:
For Hydrated compounds, add water to the end of the formula. The
number of waters is indicated by the prefix (Tri in this case = 3)
 1+
CuF®3H2O
Fluoride  F
Fluoride  1-
Practice: Try the following problems
1.
Use the table provided to help you determine the formulas of the following ionic compounds.
Name
Symbol
of
metal
Charge of Symbol of
metal
non-metal
(or
polyatomic
ion)
Charge
of nonmetal
Is there water Formula
present(Y/N)
? How many?
Potassium Oxide
Barium Nitride
Lithium Iodide
Cesium Nitrate
Iron(II)Bromide
Iron(III) Chloride
Silver(I) Carbonate
Beryllium
Phosphide
Manganese (II)
Nitrite
Potassium Fluoride
Dihydrate
Nickel(II)Oxide**
Lead (IV) Sulfide**
Magnesium
Cyanide
Tetrahydrate
Titanium
(II)Chlorate
Ammonium
Chloride
2.
Write the formulas for the following ionic compounds:
a. Sodium Sulfide
____________________
b. Calcium Nitrate
____________________
c. Strontinum Oxide
____________________
d. Copper(II) Sulfate Pentahydrate
____________________
e. Mercury(I) Phosphate
____________________
List of Polyatomic Ions:
Nitrate = NO3-
Chlorate = ClO3-
Cyanide = CN-
Phosphate = PO43-
Sulfate = SO42-
Carbonate = CO32-
Nitrite = NO2-