Chemical Nomenclature

Naming Inorganic Compounds

Ionic compounds
Covalent compounds

Naming Ionic Compounds

This section summarizes the steps needed to systematically name ionic compounds. There are three different types covered here. Those are the compounds that contain:

Monatomic ions
Polyatomic ions
Ions with variable charges

Compounds containing monatomic ions

For compounds containing monatomic ions such as Na+, Al³⁺, O²⁻and Cl^-:

Name the cation (positive ion or metal ion);
Name the anion (negative ion or nonmetallic ion) and replace the ending with the suffix "-ide."

Example 1

Name the following ionic compounds:

1.NaCl

Answer

This compound has two monatomic ions: cation Na+ and anion Cl^-. The name of the cation is sodium and the name of the anion is chlorine. Following the rules above, the name of NaCl becomes "sodium chloride," replacing the "ine" of the anion with the suffix "ide."

2. Mg₃N₂

Answer

This compound has two monatomic ions: cation Mg²⁺ and anion N^3-. The name of the cation is magnesium and the name of the anion is nitrogen. Following the rules above, the name of Mg₃N₂ becomes "magnesium nitride," replacing the "ogen" of the anion with the suffix "ide."

3. CaI₂

Answer

This compound has two monatomic ions: cation Ca²⁺ and anion I^-. The name of the cation is calcium and the name of the anion is iodine. Following the rules above, the name of CaI₂ becomes "calcium iodide," replacing the "ine" of the anion with the suffix "ide."

Compounds Containing Polyatomic Ions

Name the cation;
Name the anion;
Put them together to form the compound name.

Note: When there is a polyatomic ion in the ionic compound, do not change the ending to "ide."

Example 1

Predict the names of the following ionic compounds:

1. CaCO₃

This compound has one cation of calcium (Ca²⁺) and one polyatomic ion: carbonate (CO₃^2-).

Therefore, the name becomes calcium carbonate.

2. K₃PO₄

This compound has one cation potassium (K⁺) and one polyatomic ion: phosphate (PO₄^3-).

Therefore, the name becomes potassium phosphate.

Compounds Containing Metal Ions with Variable Charges

Many of the transition metals can produce two or more cations (positive ions) with various charges. One example is Iron; it can either produce Fe²⁺ or Fe³⁺. A list of metal ions with variable charges is given in a table at the end of this page.

Since these transition metals can take more than one charge, the charge should be specified when naming these compounds. Roman numerals are used in a bracket after the name of the cation to indicate the charge it is taking.

Example 1

Predict the names of the following ionic compounds:

1. FeCl₃

Fe, in this case, is a transition metal that takes a +3 charge. Therefore, the name becomes iron(III) chloride. Note that the suffix of chlorine anion is changed to "ide" as mentioned in the rules above, and the + charge is mentioned in the name using the roman numeral (III). Ferrous chloride is another name for iron(III) chloride. A list of alternate compound names is also given in the table below.

2. CuSe

Selenium (Se) has a -2 charge in this case, so the charge of copper (Cu) is +2. The name thus becomes copper(II) selenide.

3.Ti₂(SO₄)₃

One sulfate polyatomic ion (SO₄^-2) has a -2 charge; three of them give a total of -6 charge. To balance that and make the compound electrically neutral, we can determine that two titanium ions have a total of +6 charge. Therefore, each titanium ion takes a charge of +3. The name of this ionic compound becomes titanium(III) sulfate.

Table 1. List of Common Polyatomic Ions

Name	Formula	Name	Formula
ammonium	NH₄⁺	iodate	IO₃^-
acetate	CH₃COO^- C₂H₃O₂^-	nitrite	NO₂^-
bromate	BrO₃^-	oxalate	C₂O₄^2-
carbonate	CO₃^2-	perchlorate	ClO₄^-
chlorate	ClO₃^-	periodate	IO₄^-
chlorite	ClO₂^-	permanganate	MnO₄^-
chromate	CrO₄^2-	peroxide	O₂^2-
cyanide	CN^-	phosphate	PO₄^3-
dichromate	Cr₂O₇^2-	phosphite	PO₃^3-
hydrogen carbonate or bicarbonate	HCO₃^-	silicate	SiO₄^4-
hydrogen sulfate or bisulfate	HSO₄^-	sulfate	SO₄^2-
hydrogen phosphate or biphosphate	HPO₄^2-	sulfite	SO₃^2-
hydroxide	OH^-	thiocyanate	SCN^-
hypochlorite	ClO^-	thiosulfate	S₂O₃^2-

Table 2. Common Metal Ions with Variable Charges

copper (I)	cuprous	Cu⁺
copper (II)	cupric	Cu²⁺
iron (II)	ferrous	Fe²⁺
iron (III)	ferric	Fe³⁺
lead (II)	plumbous	Pb²⁺
lead (IV)	plumbic	Pb⁴⁺
mercury (I)	mercurous	Hg₂²⁺
mercury (II)	mercuric	Hg²⁺
tin (II)	stannous	Sn²⁺
tin (IV)	stannic	Sn⁴⁺

Naming Covalent Compounds

Name the first non-metal;
Name the second non-metal and change the ending to "-ide";
Use the prefixes such as "mono-," "di-" etc. to indicate the number of elements.
- If "mono-" is the prefix for the first element, then it doesn't have to be included in the name.

Example

Name the following compound:

1.SO₂

This compound has one sulfur and two oxygens. The first element has mono- as a prefix, so it is not included in the name, as explained above. The second element has a prefix of di- because there are two of them. Then, the suffix of the second element is changed to -ide, leading to the name sulfur dioxide,

Table 3. Nomenclature Prefixes for Covalently Bonded Compounds

Number	Prefix
1	mono-
2	di-
3	tri-
4	tetra-
5	penta-
6	hexa-
7	hepta-
8	octa-
9	nona-
10	dec-

Table 4. Examples of Covalently Bonded Species and Their Names

Chemical Formula	Name
SF₆	sulfur hexafluoride
NO₂	nitrogen dioxide
P₄O₁₀	tetraphosphorus decaoxide
Cl₂O₇	dichlorine heptoxide
N₂O₃	dinitrogen trioxide

Chemistry

Attribution

Chemical Nomenclature

Naming Covalent Compounds