Apply IUPAC nomenclature to name and write formulae for ionic, covalent and simple organic compounds

What this dot point is asking

VCAA wants you to name and write formulae for ionic, covalent and simple organic compounds following IUPAC conventions.

Ionic compounds

Cation first, anion second

Sodium chloride: Na$^+$ Cl$^-$ $\to$ NaCl.

Balance charges

Total positive charge equals total negative charge.

Variable-valency metals

Use Roman numerals to specify oxidation state. Iron(II) = Fe$^{2+}$; iron(III) = Fe$^{3+}$.

Polyatomic ions

Common ones to know:

• Nitrate NO$_3^-$, sulfate SO$_4^{2-}$, phosphate PO$_4^{3-}$, carbonate CO$_3^{2-}$, hydroxide OH$^-$, ammonium NH$_4^+$, acetate CH$_3$COO$^-$.

Covalent compounds (binary, non-metal-non-metal)

Prefixes specify the number of each atom. Mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-.

First element keeps its name; second gets "-ide" suffix.

Examples: CO carbon monoxide, CO$_2$ carbon dioxide, N$_2$O dinitrogen monoxide, N$_2$O$_5$ dinitrogen pentoxide, SF$_6$ sulfur hexafluoride.

Drop "mono-" on the first element (CO is carbon monoxide, not "monocarbon monoxide").

Simple organic compounds

Root names based on carbon chain length: meth- (1), eth- (2), prop- (3), but- (4), pent- (5), hex- (6).

Suffixes:

• -ane: alkane (single bonds, e.g. propane CH$_3$CH$_2$CH$_3$).
• -ene: alkene (one double bond).
• -yne: alkyne (one triple bond).
• -ol: alcohol (e.g. ethanol).
• -oic acid: carboxylic acid (e.g. ethanoic acid).
• -al: aldehyde.
• -one: ketone.
• -amine: amine.

Acids

Common Australian school acids:

• HCl hydrochloric acid.
• H$_2$SO$_4$ sulfuric acid.
• HNO$_3$ nitric acid.
• CH$_3$COOH ethanoic acid (acetic acid).
• H$_3$PO$_4$ phosphoric acid.

Worked example

Name FeCl$_3$.

Iron with chloride. Chloride is $-1$; for neutral compound, iron is $+3$. So Fe$^{3+}$: iron(III) chloride.

Common traps

Forgetting charge balance in ionic

Aluminium sulfate is Al$_2$(SO$_4$)$_3$, not AlSO$_4$.

Brackets for polyatomic ions when needed

When more than one polyatomic ion is needed, use brackets: Al$_2$(SO$_4$)$_3$, Mg(NO$_3$)$_2$.

Using "mono" on first element of covalent name

CO is carbon monoxide, not monocarbon monoxide.

Variable-valency metal without Roman numerals

Iron oxide is ambiguous (FeO or Fe$_2$O$_3$); specify iron(II) or iron(III).

In one sentence

IUPAC nomenclature names ionic compounds with cation first, anion second, and charges balanced (using Roman numerals for variable-valency metals); covalent compounds use numerical prefixes (di-, tri-, tetra-...) and the "-ide" suffix; simple organic compounds use root names (meth-, eth-, prop-) plus suffixes (-ane, -ene, -ol, -oic acid).

Examples in context

Example 1. Orica Yarraville ammonium nitrate plant labelling. Orica's Yarraville site produces and labels bulk chemicals shipped across Victoria. The principal product, ammonium nitrate, is named from the cation $\text{NH}_4^{+}$ and the anion $\text{NO}_3^{-}$, giving the formula $\text{NH}_4 \text{NO}_3$ with a $1:1$ charge balance. Site safety placards must show the IUPAC name on the manifest, not the trade name. A truck carrying ammonium sulfate fertiliser, $(\text{NH}_4)_2 \text{SO}_4$, needs brackets around the polyatomic cation because two are required to balance the $2-$ charge on sulfate. The same product is sometimes mislabelled "ammonium sulphate"; modern IUPAC has standardised on "sulfate" with an f.

Example 2. Bass Strait natural gas composition for ExxonMobil. Esso Australia at Longford reports the composition of natural gas piped from the Gippsland Basin. The major component is methane, $\text{CH}_4$, a simple alkane with a one-carbon root and the -ane suffix. Trace components include ethane ($\text{CH}_3 \text{CH}_3$), propane ($\text{C}_3 \text{H}_8$), carbon dioxide ($\text{CO}_2$, named with the di- prefix on oxygen) and dinitrogen ($\text{N}_2$). When the gas is sweetened, hydrogen sulfide ($\text{H}_2 \text{S}$) is removed by reaction with an amine such as monoethanolamine. The IUPAC names are the only ones accepted on Material Safety Data Sheets sent to regulators.

Try this

Q1. Write the IUPAC name and formula for each: (a) the compound formed between magnesium and phosphate, (b) the compound formed between copper(II) and hydroxide. [2 marks]

• Cue. (a) Magnesium phosphate, $\text{Mg}_3 (\text{PO}_4)_2$. (b) Copper(II) hydroxide, $\text{Cu(OH)}_2$.

Q2. A binary covalent compound of nitrogen and oxygen has the formula $\text{N}_2 \text{O}_4$. (a) Name the compound. (b) State why a prefix is needed on the nitrogen in this name but not in carbon dioxide. [3 marks]

• Cue. (a) Dinitrogen tetroxide. (b) Two nitrogens must be signalled; the "mono-" prefix is dropped on the first element only when one atom is present, as in carbon dioxide.

Q3. (a) Write the formula for iron(III) sulfate. (b) Explain why brackets are needed. (c) Compare and contrast the naming rules used for ionic compounds versus simple binary covalent compounds. [2+2+2 marks]

• Cue. (a) $\text{Fe}_2 (\text{SO}_4)_3$. (b) Three polyatomic sulfate units must be enclosed; without brackets the formula becomes ambiguous. (c) Ionic: cation then anion, balance charges, Roman numeral for variable valency. Covalent: use Greek prefixes; no charges involved.