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Chemical Nomenclature

Naming Inorganic Compounds

  1. Ionic compounds
  2. 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:

  1. Monatomic ions
  2. Polyatomic ions 
  3. Ions with variable charges

Compounds containing monatomic ions

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

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

Example 1

Name the following ionic compounds:



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


This compound has two monatomic ions: cation Mg2+ and anion N3-. 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


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. CaCO

This compound has one cation of calcium (Ca2+ and one polyatomic ion: carbonate (CO32-).

Therefore, the name becomes calcium carbonate.

2. K3PO4

This compound has one cation potassium  (K+ and one polyatomic ion: phosphate (PO43-).

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


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-



nitrite NO2-
bromate BrO3- oxalate C2O42-
carbonate CO32- perchlorate ClO4-
chlorate ClO3- periodate IO4-
chlorite ClO2- permanganate MnO4-
chromate CrO42- peroxide O22-
cyanide CN- phosphate PO43-
dichromate Cr2O72- phosphite PO33-

hydrogen carbonate



HCO3- silicate SiO44-

hydrogen sulfate



HSO4- sulfate SO42-

hydrogen phosphate



HPO42- sulfite SO32-
hydroxide OH- thiocyanate SCN-
hypochlorite ClO- thiosulfate S2O32-

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.


Name the following compound:


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


dichlorine heptoxide


dinitrogen trioxide


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