Download NOMENCLATURE OF IONIC COMPOUNDS CHEMISTRY 1405

NOMENCLATURE OF IONIC COMPOUNDS
CHEMISTRY 1405 HANDOUT

All ionic compounds are neutral.

Oxidation number refers to the number of electrons lost or gained by an atom.

Every ionic compound consists of cationic part and an anionic part. The cationic part is derived
from the metal and the anionic part is derived from the non-metal.

The cationic part is written before the anionic part.

The name of the cation is the same as that of the metal.

The name of the anion is not the same as that of the non-metal. Refer to the handout # and # to
learn the names of all the anions.

Example 1: Write the formula of the ionic compound zinc oxide.

This compound is composed of two parts – cationic part ie Zn and anionic part ie O .

The total positive charge should equal the total negative charge. In this case, a positive charge
+2
-2
of +2 is balanced by a negative charge of -2.

Combining the two ions we get the formula of zinc oxide as ZnO.

Example 2: Write the formula of the ionic compound calcium bromide.

This compound is composed of two parts – cationic part ie Ca and anionic part ie Br .

The total positive charge should equal the total negative charge. In this case, the total positive
+2
-1
charge is +2 and the negative charge is -1. In order, to maintain neutrality, we need another
bromide ion. So the overall negative charge is -2.
+2

-1
Combining one Ca ion and two Br ions, the formula of calcium bromide is expressed as
CaBr .
2

Example 3: Write the fomula of the compound Copper (II) nitrate.

This compound is composed of two parts – cationic part that is identified as Cu ion. The
+2
Roman Numeral 2 within parenthesis is identified as the oxidation number of the cation.
-1

The anionic part is NO .
3

The overall positive charge is +2 and the negative charge is only -1. Hence, we need another
nitrate ion in order to balance the overall positive charge.
+2

-1
Combining one Cu ion with two NO
3
ions, the formula of the compound copper (II) nitrate
is written as Cu(NO ) .
3 2

Note: When there are more than one polyatomic ions, the number of ions is written as a
subscript outside the parenthesis. For example, three sulfate ions are written as (SO ) and not
4 3
as SO
.
4, 3

Example 4: Write the name of the compound Ba(OH) .
2

The cationic part is named first ie Barium.

The anionic part is named later ie hydroxide.

Combining the cationic and anionic part, the name of the ionic compound is barium hydroxide.

Common errors: One may be tempted to write the anionic part as dihyroxide and it is incorrect.
The prefixes mono, di, tri, tetra etc are used only for binary covalent compounds.

One may be tempted to put the oxidatiion number of Barium within parenthesis such as Barium
(II) and this is incorrect. Oxidation number is expressed in parenthesis only for transistion metal
ions or metal ions which show variable oxidation numbers. Barium belongs to group 2 and all
elements in group 2 have a fixed oxidation number of +2.

Example 5: Write the name of the compound FeCl .
3

The cationic part in this compound is iron and the anionic part is chloride.

Iron is a transition metal ion with an oxidation number of +3. Each chloride has a charge of -1
and there are three chlorides to balnce the overall positive charge of +3.

The name of the compound FeCl is expressed as Iron (III) chloride.
3