WK I WRITING CHEMICAL FORMULAS
Name
Aluminum ion
Ammonium ion
Calcium ion
Formula
Al+3
NH+4
Ca+2
Table of Some Common Ions
Name
Formula
Bromide ion
BrChloride ion
ClFluoride ion
F-
Lithium ion
Potassium ion
Sodium ion
Strontium ion
Li+
K+
Na+
Sr+2
Iodide ion
Nitride ion
Oxide ion
Sulfide ion
Common Polyatomic Ions:
Ion/Charge
Name
-1
OH
Hydroxide
SO4-2
Sulfate
-2
SO3
Sulfite
NO3-1
Nitrate
-1
NO2
Nitrite
PO4-3
Phosphate
+1
NH4
Ammonium
IN-3
O-2
S-2
Name
Carbonate ion
Cyanide ion
Hydrogen
carbonate ion
Hydroxide ion
Nitrate ion
Phosphate ion
Sulfate ion
Formula
CO3-2
CNHCO3OHNO3PO4-3
SO4-2
Ionic Charges by Group Number
Group
Charge
Number
#1
+1
#2
+2
#13
+3
#14
Share
#15
share or -3
#16
-2
#17
-1
Sample Problem #1:
Write the ionic formula for tungsten (IV) oxide.
1. List the symbols for each ion
Symbol for tungsten (IV) ion: W+6 (IV indicates a charge of +6) Symbol for oxide ion: O-2
2. Write the symbols for the ions, side by side, with the cation first
W+6 O-2
3. Find the least common multiple of the ion’s charges.
The least common multiple of 6 and 2 is 6. To get a neutral compound, you need a total of six positive charges
and six negative charges. To get six positive charges, you need one W+6 ion, because 1x 6+ =6+
To get six negative charges, you need three O-2 ions, because 3 x -2 = -6
4. Write the chemical formula, using subscripts to indicate how many of each ion are needed to make a
neutral compound.
WO3
Sample Problem #2:
Write the ionic formula for lithium phosphate.
1. List the symbols for each ion
Symbol for lithium: Li+
Symbol for phosphate: (PO4)-3
2. Write the symbols for the ions, side by side, with the cation first
Li+ (PO4)-3
3. Find the least common multiple of the ion’s charges.
The least common multiple of 1 and 3 is 3. To get a neutral compound, you need a total of 3 positive charges
and 3 negative charges. To get 3 positive charges, you need 3 Li+ ion, because 3x +1 = +3
To get six negative charges, you need 1 (PO4)-3 ion, because 1 x -3 = -3
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4. Write the chemical formula, using subscripts to indicate how many of each ion are needed to make a
neutral compound.
Li3PO4
Write the correct chemical formulas for the following (if it is an ionic compound write each ion first):
1. calcium phosphate
2. aluminum sulfate
3. phosphorus trichloride
4. ammonium sulfide
5. sodium hydroxide
6. carbon dioxide
7. diphosphorus pentaoxide
8. potassium chloride
9. lithium sulfide
10. sulfur dioxide
11. calcium oxide
12. carbon monoxide
13. aluminum sulfate
14. magnesium oxide
15. dinitrogen monoxide
16. lithium sulfate
17. sodium chloride
18. barium nitrate
19. sulfur tetrafluride
20. sodium nitrate
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