O Level Combined Science 5129 · Topic 14

Atoms, elements and compounds: past paper questions

247 real questionsasked in 10 of the last 10 exam series2019–2025usually: State, Describe, Complete, Explain, Deduce

Real questions on atoms, elements and compounds

The newest 20 of 148 written questions, plus 99 multiple-choice. Open one to see it on the real paper.

5129/21 · October/November 2025 · Q9a[4]
Describe how useful electrical power may be obtained from nuclear fuel.
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5129/21 · October/November 2025 · Q9b[1]
Describe one advantage of using nuclear fuel to produce electrical power.
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5129/31 · October/November 2025 · Q2d[3]
When the student does the flame test on the filtrate, the flame turns yellow. When barium nitrate is added to the filtrate, a white precipitate is formed. Use these observations and the conclusion made in (c) to identify three ions that are present in the filtrate.
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5129/21 · May/June 2025 · Q2b[1]
When potassium, K, reacts with water, potassium hydroxide, KOH, and hydrogen are formed. 2KOH + H 2 The relative atomic masses, A r , of hydrogen, oxygen and potassium are shown. [A r : H, 1; O, 16; K, 39] Calculate the mass of water that reacts with 3.9 g of potassium. mass = g 2K + 2H 2 O
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5129/21 · May/June 2025 · Q2c[1]
State the name of the gas produced when lithium reacts with water.
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5129/21 · May/June 2025 · Q2d[1]
Aluminium is a reactive metal but does not appear to react with water. Explain why.
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5129/21 · May/June 2025 · Q5d[1]
The formula of silver bromide is AgBr. Suggest the formula of silver chloride.
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5129/21 · May/June 2025 · Q11a(ii)[2]
Describe how the electronic configuration changes when the atom of the element forms a +2 ion.
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5129/21 · May/June 2025 · Q11b[1]
State the word used for a positive ion.
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5129/21 · May/June 2025 · Q16b(ii)[1]
Carbon dioxide, CO 2 , is present in air. Explain why carbon dioxide is a gas at room temperature and pressure.
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5129/21 · May/June 2025 · Q16b(iii)[1]
A gas can be condensed by lowering the temperature. Describe one other way of condensing a gas.
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5129/22 · May/June 2025 · Q5a(i)[1]
Give the state symbol for an aqueous solution.
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5129/22 · May/June 2025 · Q5a(ii)[2]
State the names of two chemicals used in the test for sulfate ions. chemical
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5129/22 · May/June 2025 · Q11a[2]
State the electronic configuration of an atom of the element found in Group III and Period 3 of the Periodic Table.
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5129/22 · May/June 2025 · Q11b[2]
The electronic configuration of an atom of nitrogen is 2,5. When nitrogen reacts with magnesium it forms an ion with a charge of –3. Describe how the electronic configuration changes when an atom of nitrogen forms an ion with a charge of –3.
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5129/22 · May/June 2025 · Q11c[1]
State the word used for a negative ion.
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5129/22 · May/June 2025 · Q14a(i)[1]
State the name of the solute.
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5129/21 · October/November 2024 · Q10b[2]
Solid sodium oxide is ionically bonded. Describe ionic bonding.
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5129/21 · October/November 2024 · Q10d[2]
Complete Fig. 10.1 to show the outer electrons in a molecule of oxygen. O O
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5129/21 · October/November 2024 · Q13b(i)[1]
Draw the displayed formula of methane, CH 4 .
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What examiners said

Only the most able candidates were able to apply the ratio of the reacting molecules to determine the correct reacting masses.
— Examiner report, October/November 2023, 5129/21 Q3(a)(ii) (Cambridge)

Some candidates recalled the number of electrons in the bonds between hydrogen and nitrogen atoms in this molecule of ammonia. They may also have used the Periodic Table to deduce that covalency between these non-metals requires two electrons in each bond (hydrogen has only one) and this leaves nitrogen with two unbonded electrons.
— Examiner report, October/November 2023, 5129/21 Q3(b)(i) (Cambridge)

Candidates should recall that substances with low boiling points have weak forces between their molecules. This is also essential for an understanding of fractional distillation.
— Examiner report, October/November 2023, 5129/21 Q3(b)(ii) (Cambridge)

Practise this topic

Answer these questions online and get each one marked against the official mark scheme, with what you missed and how to fix it.

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In the syllabus

14.1 Elements, compounds and mixtures

Describe the differences between elements, molecules, compounds and mixtures
Describe a: (a) solvent as a substance that dissolves a solute (b) solute as a substance that is dissolved in a solvent (c) solution as a mixture composed of one or more solutes dissolved in a solvent
Describe how to use paper chromatography to separate mixtures of soluble substances, using a suitable solvent
Interpret simple chromatograms to identify: (a) unknown substances by comparison with known substances (b) pure and impure substances

14.2 Atomic structure and the Periodic Table

Describe the structure of the atom as a central nucleus containing neutrons and protons surrounded by electrons in shells
State the relative charges and relative masses of a proton, a neutron and an electron
Define proton number / atomic number as the number of protons in the nucleus of an atom
Define mass number / nucleon number as the total number of protons and neutrons in the nucleus of an atom
Determine the electronic configuration of elements with proton number 1 to 20, e.g. 2,8,3
State that: (a) Group VIII, the noble gases, are unreactive monatomic gases, with a full outer shell, e.g. 2,8 (b) the number of outer shell electrons is equal to the group number in Groups I to VII (c) the number of occupied electron shells is equal to the period number

14.3 Ions and ionic bonds

Describe the formation of positive ions, known as cations, and negative ions, known as anions, with noble gas electronic configurations
Describe the giant lattice structure of ionic compounds as a regular arrangement of alternating positive and negative ions
State that an ionic bond is a strong electrostatic attraction between oppositely charged ions
Describe the formation of ionic bonds between ions of metallic and non-metallic elements, including between sodium and chlorine to form NaCl and magnesium and chlorine to form MgCl 2
Use dot-and-cross diagrams to show the formation of ionic bonds
Describe and explain in terms of structure and bonding the properties of ionic compounds: (a) high melting points and boiling points (b) good electrical conductivity when aqueous or molten and poor when solid

14.4 Simple molecules and covalent bonds

State that a covalent bond is formed when a pair of electrons is shared between two atoms leading to noble gas electronic configurations
Describe the formation of covalent bonds in simple molecules, including H2, Cl 2, H2O, CH4, NH3, HCl , O2 and CO2. Use dot-and-cross diagrams to show the electronic configurations in these and similar molecules.
Describe and explain in terms of structure and bonding the properties of simple molecular compounds: (a) low melting points and boiling points in terms of weak intermolecular forces (specific types of intermolecular forces are not required) (b) poor electrical conductivity

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