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Writing Chemical Formulas

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Writing Chemical Formulas

A labelling mix-up has left a set of compounds without formulas. Use ion charges, atom counts and chemical naming rules to restore the labels. For ionic compounds, make the total charge zero and use the simplest whole-number ratio. Use brackets around a polyatomic ion when more than one is needed.

Ion reference panel

Use these common ions for the questions below. The charge applies to the entire ion.

Positive ion

Charge

Negative ion

Charge

Na⁺

Cl⁻

−1

Mg²⁺

O²⁻

−2

Al³⁺

SO₄²⁻

−2

Ca²⁺

NO₃⁻

−1

Restore the formula labels

Show working where a formula needs more than one ion or atom.

1.Choose the correctly written formula for sodium chloride.

NaCl
NaCl₂
Na₂Cl
Na₂Cl₂

2.Magnesium ions and oxide ions combine in the simplest neutral ratio. Write the formula for magnesium oxide and state the total charge contributed by each ion in one formula unit.

3.Aluminium sulphate contains Al³⁺ ions and SO₄²⁻ ions. Work out the smallest whole-number ratio of ions and write the compound formula.

4.Calcium nitrate is made from Ca²⁺ and NO₃⁻. Write its formula, using brackets where needed, and explain what the subscript outside the brackets counts.

5.A student writes Mg₂O₂ for magnesium oxide because the charges are 2+ and 2−. Correct the formula and explain why the student's version is not written in the simplest form.

6.Match each molecular name to its formula. Use the prefixes mono- (one), di- (two) and tri- (three).

carbon dioxide
carbon monoxide
dinitrogen trioxide

CO
N₂O₃
CO₂

7.A sealed sample contains molecules with 2 carbon atoms and 4 hydrogen atoms per molecule. Write its molecular formula. Do not reduce the subscripts.

8.True or false: In the formula Ca(NO₃)₂, there are two nitrogen atoms and six oxygen atoms. Correct the statement if it is false.

TrueFalse

9.A compound contains 2.0 mol of carbon atoms and 4.0 mol of hydrogen atoms. Find its empirical formula, the simplest whole-number atom ratio.

10.A compound has empirical formula CH₂ and relative molecular mass 56. The empirical formula mass is 14. Calculate the molecular formula and show how many empirical-formula units are present in one molecule.

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Writing Chemical Formulas

Writing Chemical Formulas

Ion reference panel

Restore the formula labels

3 printable pages

About This Worksheet

Free in Kuraplan

Print-Ready

AI-Generated

For Teachers & Parents

Need a custom version of this worksheet?

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