NOTES/ WKSTs: Naming Ions and
Binary Ionic Compounds and
Writing Formulas from Compound Names
Name______________________________
Date__________ Block_____
I. Naming Ions
For metal ions: use the element name with the word “ion” written after it. The
word “ion” MUST be included to distinguish the ion from the element.
Na+1
sodium ion
Ca+2
calcium ion
Al+3
aluminum ion
For nonmetal ions: the element name is given an -ide ending.
C-4
carbide ion
P-3
phosphide ion
N-3
nitride ion
S-2
sulfide ion
O-2
oxide ion
Cl-1
chloride ion
F-1
fluoride ion
Br-1
bromide ion
I-1
iodide ion
II. Naming Binary Compounds When Given the Chemical Formula
Binary ionic compounds are composed of two ions, a positive ion (a metal ion) and a negative
ion (a nonmetal ion). The positive ion (metal ion) is ALWAYS written first in the formula and
therefore the compound name BEGINS with the name of the positive ion. The name of the
positive ion is the same as the element name. The negative ion name takes an –ide ending.
For example: the ion of sodium is the sodium ion, Na +1;
the ion of chlorine is the chloride ion, Cl –1.
When naming any ionic compound, the word “ion” is not used. It is understood that ions are
involved in ionic compounds. Thus, the ionic compound NaCl is simply sodium chloride.
The subscripts used in the formulas are not used in the names of ionic compounds. For
example, MgCl2 is named magnesium chloride. It is incorrect to name this compound
magnesium chloride “two”. The subscripts are used in the formulas to balance the numbers of
positive and negative electrical charges.
For naming binary ionic compounds, write the name of the cation (positive metal ion) first,
then write the name of the anion (negative nonmetal ion) using the –ide ending. The word
“ion” is NOT used when writing compound names. Also, no reference is made to any
numerical subscripts that may be in the formula.
Examples of binary ionic formulas and their correct names:
NaCl
sodium chloride
BaO
barium oxide
LiF
lithium fluoride
Na3N
sodium nitride
CaCl2
calcium chloride
Na2O
sodium oxide
III. Writing Binary Ionic Formulas When Given the Compound Name
When writing formulas for binary ionic compounds, first write the ions with the correct charges.
Then write the element symbols without the charges, placing the metal first. Now balance the
electrical charges. The net charge on the compound must be zero. (Always ask yourself: How
many positive charges are needed to balance the negative charges?)
Example #1: sodium chloride
ions needed:
Na+1
and Cl-1
Since each ion has one unit of charge, only one of each ion is needed in the formula, and no
subscripts are used.
The formula for sodium chloride is NaCl.
Example #2: sodium oxide
ions needed:
Na+1
and O-2
Sodium ion has 1 unit of positive charge while the oxide ion has 2 units of negative charge.
Therefore, 2 units of positive charge are required to balance the 2 units of negative charge.
A subscript “2” written after the sodium symbol will indicate that there are 2 sodium ions.
The formula for sodium oxide is Na2O.
Example #3:
magnesium nitride
ions needed: Mg+2
and N-3
Each magnesium ion has 2 units of positive charge. Each nitride ion has 3 units of negative
charge. To calculate how many of each ion are needed to have the net charge be zero: use the
least common multiple: 2 x 3 = 6.
How many magnesium ions are needed to give a total positive charge of 6+? Each magnesium
ion has a charge of +2; so 6 divided by 2 equals 3. Three magnesium ions are needed.
How many nitride ions are needed to give a total negative charge of 6-? Each nitride ion has a
charge of –3; so 6 divided by 3 equals 2. Two nitride ions are needed.
The formula for magnesium nitride is Mg3N2.
For any ionic compound, the total number of positive charges MUST balance the
total number of negative charges. The net charge MUST be zero.
First, write the ion symbols over the name of each ion. (This will help you learn the names and
correct formulas for each of the ions!) Then write the correct formula.
Na+1
Cl-1
sodium chloride
NaCl
Ba+2
F-1
barium fluoride
BaF2
K+1
O-2
potassium oxide
K2O
I. For each of the following, if given the ion symbol, write the correct name; if given the
ion name, write the correct symbol.
ION NAME
ION SYMBOL
ION SYMBOL
ION NAME
lithium ion
N-3
magnesium ion
O-2
strontium ion
F-1
potassium ion
P-3
zinc ion
Cl-2
silver ion
Br-1
calcium ion
S-2
sodium ion
Au+1
carbon ion
C -4
boron ion
I-1
II. Name the following binary ionic compounds:
1. KF
________________________________________________
2. CaO
________________________________________________
3. BaS
________________________________________________
4. Al2O3
________________________________________________
5. Li2O
________________________________________________
6. Mg3P2
________________________________________________
7. ZnCl2
________________________________________________
8. Na3N
________________________________________________
9. Ba3N2
________________________________________________
10. CaBr2
________________________________________________
III. Write the correct balanced formulas for each of the following binary ionic compounds.
(Hint: write the ion symbol over the name of each ion in the binary ionic compound name.)
1. calcium phosphide
___________________
2. potassium chloride
___________________
3. magnesium oxide
___________________
4. lithium fluoride
___________________
5. barium nitride
___________________
6. sodium sulfide
___________________
7. aluminum phosphide
___________________
8. aluminum oxide
___________________
9. aluminum bromide
___________________
10. silver chloride
___________________
11. silver sulfide
___________________
12, zinc oxide
___________________
13. magnesium nitride
___________________
14. potassium nitride
___________________
15. sodium carbide
___________________
16. barium fluoride
___________________
17. calcium chloride
___________________
18. calcium nitride
___________________
19. zinc phosphide
___________________
20. beryllium bromide
___________________
IV. For each of the following, name the compound if the formula is given; write the
correct formula if the compound name is given.
Binary Ionic
Formula
Compound Name
Compound Name
NaF
barium sulfide
CaCl2
sodium phosphide
Li2O
lithium bromide
MgO
potassium oxide
KCl
calcium oxide
KI
silver phosphide
BaBr2
strontium carbide
Al2S3
aluminum phosphide
Ag2O
calcium iodide
Ca3P2
potassium sulfide
AlF3
magnesium fluoride
Na4C
lithium sulfide
HF
calcium phosphide
MgI2
aluminum fluoride
Binary Ionic
Formula