Naming Inorganic Compounds Revision Notes for HSC SSCE Chemistry

Naming Inorganic Compounds

Understanding chemical nomenclature

Chemistry relies on a systematic way of naming compounds so that scientists worldwide can communicate clearly. The International Union of Pure and Applied Chemistry (IUPAC) develops these naming rules, known as chemical nomenclature. This standardised system ensures that everyone uses the same names for the same substances.

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IUPAC has created different guides for naming different types of compounds:

The Red Book contains rules for naming inorganic compounds (compounds that generally don't contain carbon)
The Blue Book covers organic compounds
The Purple Book deals with polymers

The naming system you learned previously is called compositional or stoichiometric naming. This tells us about the composition of a compound based on its formula, but doesn't provide information about its structure.

Acids and bases in everyday life

Before we look at naming rules, it's helpful to recognise that acids and bases are all around us in nature and in our homes.

Common acids include:

Rain (slightly acidic)
Citrus fruits (citric acid)
Soft drinks (carbonic acid)
Vitamin C (ascorbic acid)
Stomach acid (hydrochloric acid)

Common bases include:

Ammonia (found in cleaning products)
Caffeine (in coffee and tea)
Baking soda
Antacids

Naming inorganic acids

What are inorganic acids?

Inorganic acids (also called mineral acids) are acids that don't contain carbon chains. The most common examples you'll work with are:

Hydrochloric acid ( $\text{HCl}$ )
Sulfuric acid ( $\text{H}_2\text{SO}_4$ )
Nitric acid ( $\text{HNO}_3$ )
Phosphoric acid ( $\text{H}_3\text{PO}_4$ )

These differ from organic acids, which are carbon-based compounds with acidic properties, such as citric acid in fruit or acetic acid in vinegar.

How to name inorganic acids

When we name an inorganic acid with the general formula $\text{HA}$ , we base the name on the anion (negatively charged ion) that forms when the acid dissolves in water.

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The compositional name of an inorganic acid is derived from the anion (A) that is formed when the acid, HA, dissociates in water to form $\text{H}^+$ and $\text{A}^-$ .

The anion can be either:

Monoatomic: a single atom (like $\text{Cl}^-$ )
Polyatomic: multiple atoms bonded together (like $\text{SO}_4^{2-}$ )

Binary acids (monoatomic anions)

When an acid contains hydrogen bonded to a single other element, we call it a binary acid. To name these acids:

Start with the prefix "hydro-"
Take the name of the anion
Replace the "-ide" ending with "-ic"
Add the word "acid"

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Worked Example: Naming a Binary Acid

Name $\text{HCl}$ , which contains the chloride ion ( $\text{Cl}^-$ ).

Step 1: Identify that this is a binary acid (hydrogen + one other element)

Step 2: Apply the naming rule:

Start with "hydro-"
Chloride → Chloric
Add "acid"

Result: Hydrochloric acid

Other examples:

$\text{HF}$ → hydrofluoric acid
$\text{HBr}$ → hydrobromic acid
$\text{H}_2\text{S}$ → hydrosulfuric acid

Oxyacids (polyatomic anions)

Oxyacids are acids that contain oxygen bonded to another element such as sulfur, nitrogen, phosphorus or carbon. The naming rules depend on whether the polyatomic ion ends in "-ate" or "-ite".

Polyatomic ions ending in "-ate"

For acids containing polyatomic ions that end in "-ate":

Take the name of the polyatomic ion
Replace "-ate" with "-ic"
Add the word "acid"

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Worked Example: Naming an Oxyacid with -ate

Name $\text{HNO}_3$ , which contains the nitrate ion ( $\text{NO}_3^-$ ).

Step 1: Identify the polyatomic ion ending: nitrate

Step 2: Apply the naming rule:

Nitrate → Nitric
Add "acid"

Result: Nitric acid

Other examples:

$\text{H}_2\text{SO}_4$ (sulfate → sulfuric) → sulfuric acid
$\text{H}_2\text{CO}_3$ (carbonate → carbonic) → carbonic acid
$\text{H}_3\text{PO}_4$ (phosphate → phosphoric) → phosphoric acid

Polyatomic ions ending in "-ite"

For acids containing polyatomic ions that end in "-ite":

Take the name of the polyatomic ion
Replace "-ite" with "-ous"
Add the word "acid"

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Worked Example: Naming an Oxyacid with -ite

Name $\text{HNO}_2$ , which contains the nitrite ion ( $\text{NO}_2^-$ ).

Step 1: Identify the polyatomic ion ending: nitrite

Step 2: Apply the naming rule:

Nitrite → Nitrous
Add "acid"

Result: Nitrous acid

Other examples:

$\text{H}_2\text{SO}_3$ (sulfite → sulfurous) → sulfurous acid
$\text{H}_3\text{PO}_3$ (phosphite → phosphorous) → phosphorous acid

Summary flowchart for naming acids

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Memory aid: Remember "ATE to IC, ITE to OUS" for polyatomic ions.

HYDRO for binary acids with HYDROGEN - if you see hydrogen combined with a single element, use the "hydro-" prefix.

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Exam tip: Always check if the acid contains a monoatomic or polyatomic anion first, as this determines which naming rule to use.

Naming inorganic bases

What are inorganic bases?

An inorganic base is a substance that contains either the hydroxide ion ( $\text{OH}^-$ ) or the oxide ion ( $\text{O}^{2-}$ ), or produces hydroxide ions when dissolved in water.

Common inorganic bases include:

Sodium hydroxide ( $\text{NaOH}$ )
Barium hydroxide ( $\text{Ba(OH)}_2$ )
Magnesium oxide ( $\text{MgO}$ )
Iron(III) oxide ( $\text{Fe}_2\text{O}_3$ )
Copper(II) hydroxide ( $\text{Cu(OH)}_2$ )
Ammonia ( $\text{NH}_3$ )

How to name inorganic bases

Metal hydroxides and oxides

Most inorganic bases are ionic compounds containing metal cations bonded to either hydroxide or oxide ions. We name these bases using the standard ionic compound naming rules:

Name the metal cation first
Name the anion second (hydroxide or oxide)

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Worked Example: Naming Metal Hydroxides and Oxides

Example 1: $\text{NaOH}$

Metal cation: Sodium
Anion: Hydroxide
Name: Sodium hydroxide

Example 2: $\text{Ca(OH)}_2$

Metal cation: Calcium
Anion: Hydroxide
Name: Calcium hydroxide

Example 3: $\text{Fe}_2\text{O}_3$

Metal cation: Iron(III) - note the Roman numeral for transition metals
Anion: Oxide
Name: Iron(III) oxide

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For transition metals that can form multiple ions, include the charge in Roman numerals.

Alkalis

Bases that dissolve in water are specifically called alkalis. The most common alkalis are:

Sodium and potassium hydroxides
Calcium and barium hydroxides
Ammonia ( $\text{NH}_3$ )

When ammonia dissolves in water, it produces ammonium ( $\text{NH}_4^+$ ) and hydroxide ( $\text{OH}^-$ ) ions, making it an alkali even though it doesn't contain hydroxide ions in its formula.

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Exam tip: All alkalis are bases, but not all bases are alkalis. Only water-soluble bases are called alkalis.

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Key Points to Remember:

IUPAC nomenclature provides standardised rules for naming chemical compounds to enable clear scientific communication.
Binary acids (containing hydrogen and one other element) are named with the prefix "hydro-", changing the anion name ending to "-ic", and adding "acid" (e.g., $\text{HCl}$ = hydrochloric acid).
Oxyacids with polyatomic anions are named by converting "-ate" endings to "-ic" and "-ite" endings to "-ous" (e.g., nitrate → nitric acid, nitrite → nitrous acid).
Inorganic bases containing hydroxide or oxide ions are named as ionic compounds, using the metal name followed by hydroxide or oxide.
Alkalis are the subset of bases that dissolve in water, including common examples like sodium hydroxide, potassium hydroxide and ammonia.

Naming Inorganic Compounds (HSC SSCE Chemistry): Revision Notes