Nomenclature Rules

Nomenclature rules are used to name elements and compounds based on their chemical formulas.

Chemical nomenclature has existed since the 18^th century. It evolved over time, leading to several nomenclature standards today. Therefore, the nomenclature rules may be different from one textbook to another.

The rules explained below were established before 2005 by the International Union of Pure and Applied Chemistry (IUPAC)^[1]. Although IUPAC released an updated guide since, the nomenclature rules established before 2005 remain the most common ones in the field of chemistry.

While formal nomenclature rules apply to all substances, some of them have alternative common names that are used very frequently. For example, $\text{H}_2 \text{O}$ is commonly referred to as water instead of dihydrogen monoxide.

An element is a substance made up of only one type of atom.

1. If an element contains a single atom, it preserves the name indicated in the periodic table with the possible addition of the word atom.

2. If an element contains more than one atom, it preserves the name indicated in the periodic table with added terminology indicating that it is a molecule.

A binary compound is a substance made of two types of atoms. Binary compounds can be covalent or ionic.

A covalent binary compound, such as $\text{P}_2 \text{O}_5$, is composed of two types of nonmetal atoms: $\text{P}$ (phosphorus) and $\text{O}$ (oxygen).

An ionic binary compound, such as $\text{NaCl}$ is composed of a metal and a nonmetal atom: $\text{Na}$ (sodium) and $\text{Cl}$ (chlorine).

1. Start by naming the atom that appears first in the chemical formula.

   1. Use the element name in the periodic table.

   2. If applicable, add a prefix (mono-, di-, tri-, etc.) to indicate the number of atoms of the element in the compound.
      Note: The prefix mono- is often omitted.

2. Name the second atom.

   1. Alter the element name, add the suffix -ide to the root.

   2. If applicable, add a prefix (mono-, di-, tri-, etc.) to indicate the number of atoms of the element in the compound.

In some instances, when the word oxide is preceded by a prefix, the last vowel of the prefix has to be removed, as shown in the following table.

Use the rules of nomenclature to name the compound with the following chemical formula: $\text{CO}_2.$

Use the nomenclature rules to name the compound with the following chemical formula: $\text{N}_2 \text{O}_4.$

What is the chemical formula of carbon monosulphide?

What is the chemical formula of diphosphorus pentoxide?

1. Start by naming the atom that appears first in the chemical formula (usually a metal) using the element name in the periodic table.

2. Name the second atom (usually a nonmetal) by altering its element name and adding the suffix -ide to the root, as shown in the reference table. 

Prefixes are not used when naming ionic compounds. The rules of chemical notation are used to indicate the number of atoms of each element in the compound.

Use the nomenclature rules to name the compound with the following chemical formula: $\text{CaCl}_2.$

Use the nomenclature rules to name the compound with the following chemical formula: $\text{Al}_2 \text{O}_3.$

What is the chemical formula of potassium iodide?

A polyatomic ion is an ion composed of several atoms.

1. Start by naming the atom or the group of atoms that appear first in the chemical formula.

   1. If the compound’s chemical formula begins with an atom (usually a metal), name it using its element name in the periodic table.

   2. If the compound’s chemical formula begins with a polyatomic ion, name it using the reference table in the previous section.

2. Name the atom or the group of atoms that appears second.

   1. If the compound’s chemical formula ends with a polyatomic ion, name it using the reference table in the previous section.

   2. If the compound’s chemical formula ends with an atom (usually a nonmetal), name it by altering its element name and adding the suffix -ide to the root, as shown in the reference table.

Prefixes are not used when naming ionic compounds with polyatomic ions. Instead, the rules of chemical notation are used to indicate the number of each ion in the compound.

Use the nomenclature rules to name the compound with the following chemical formula: $\text{KClO}_3.$

Use the nomenclature rules to name the compound with the following chemical formula: $\text{Mg(NO}_3 \text{)}_2.$

Use the nomenclature rules to name the compound with the following chemical formula: $\text{NH}_4 \text{F}.$

What is the chemical formula of sodium nitrate?