2 Natural gas and petroleum are two types of fossil fuel. (a) Name one other fossil fuel. … [1] (b) State the main constituent of natural gas. … [1] (c) Petroleum is separated by the process shown in Fig. 2.1. petroleum gasoline gas oil naphtha bitumen refinery gas Fig. 2.1 (i) Name this process. … [1] (ii) State one use for bitumen. … [1] (d) Ethane and ethene are both hydrocarbons. Ethane is an alkane. Ethene is an alkene. (i) Two compounds are made during the complete combustion of ethane and of ethene. Water is one of these compounds. Identify the other compound. … [1] (ii) Describe one difference between molecules of ethane and molecules of ethene. … … [1] (e) The structure of a molecule of another hydrocarbon is shown in Fig. 2.2. H H H C H H C H H C H Fig. 2.2 Deduce the formula of this hydrocarbon. … [1] [Total: 7]

2(a) coal ; 1 2(b) methane / CH4 ; 1 2(c)(i) fractional distillation ; 1 2(c)(ii) (for making) roads ; 1 2(d)(i) carbon dioxide / CO2 ; 1 2(d)(ii) ethene, is unsaturated / contains double bonds ; 1 2(e) C3H8 ; 1

2 (a) Fig. 2.1 shows part of Group I of the Periodic Table. lithium 7 3 Li sodium 23 11 Na potassium 39 19 K Fig. 2.1 (i) State the trend in the reactivity of the elements going down Group I. … [1] (ii) Explain why lithium does not react with helium, a Group VIII element. … … [1] (iii) Lithium is a solid and helium is a gas. Describe two differences between the structures of a solid and a gas. 1 … … 2 … … [2] (b) A piece of sodium is added to water, as shown in Fig. 2.2. sodium water Fig. 2.2 The sodium reacts with water. The reaction is exothermic. (i) State one other observation that is seen when sodium reacts with water. … [1] (ii) Complete the word equation for the reaction of sodium with water. sodium + water + [2] (c) X is a compound that reacts with dilute hydrochloric acid to form sodium chloride and water. Suggest the identity of X. … [1] (d) Concentrated aqueous sodium chloride is broken down by electrolysis. (i) State the type of chemical bond in sodium chloride. … [1] (ii) Identify the product that forms at the anode (positive electrode). … [1] [Total: 10]

2(a)(i) increasing / more reactive / faster reaction ; 1 2(a)(ii) helium / He is, unreactive / inert ; 1 2(a)(iii) any two from: (solid/lithium) particles close(r) (together) ORA ; (solid/lithium) particles regular arrangement ORA ; (solid/lithium) particles vibrate / not free-moving ORA ; 2 2(b)(i) fizzes / bubbles OR gets smaller / disappears OR moves around ; 1 2(b)(ii) sodium + water → sodium hydroxide + hydrogen in either order sodium hydroxide ; hydrogen ; 2 2(c) sodium hydroxide / NaOH OR sodium carbonate / Na2CO3 ; 1 2(d)(i) ionic ; 1 2(d)(ii) chlorine / Cl2 ; 1 (a)(i) You must state that the reactivity of Group I elements increases as you go down the group. (a)(ii) You need to explain that helium is unreactive or inert. (a)(iii) You must describe two differences between the structure of a solid and a gas, such as particle spacing (closer in solid), arrangement (regular in solid), or movement (vibrating in solid, free-moving in gas). (b)(i) You need to describe an observable change when sodium reacts with water, such as fizzing, bubbling, getting smaller, disappearing, or moving around. (b)(ii) You must correctly identify both products of the reaction: sodium hydroxide and hydrogen. (c) You need to name a suitable substance that turns universal indicator purple, such as sodium hydroxide or sodium carbonate. (d)(i) You must state that the bonding in sodium chloride is 'ionic'. (d)(ii) You need to identify 'chlorine' as the other product formed when sodium reacts with a Group VII element.

2 (a) A mixture contains water, dissolved sodium chloride and an insoluble solid compound. (i) State what is meant by insoluble and compound. insoluble … … compound … … [2] (ii) Describe how crystals of sodium chloride are obtained from this mixture. … … … … … [3] (b) Water is a covalent molecule. Complete Fig. 2.1 to show the dot-and-cross diagram of a molecule of water. Show all the outer shell electrons. H O H Fig. 2.1 [2] (c) An atom of oxygen contains 8 electrons and it has the nucleon number (mass number) 16. State what is meant by nucleon number. … … [1] (d) Complete Table 2.1 to show the charges and approximate relative masses of neutrons and protons. Table 2.1 particle charge relative mass neutron proton [2] [Total: 10]

2(a)(i) insoluble: cannot / does not, dissolve (in water) ; compound: two (or more) elements (chemically) combined ; 2 2(a)(ii) any three from: filter (at the start) / filter (off the insoluble solid) ; evaporate / heat (the NaCl solution) ; leave to (cool and) crystallise ; filter off the crystals / dry between folds of filter paper ; 3 2(b) two bond pairs ; two lone pairs on O ; 2 2(c) (the total number of) protons and neutrons (in the nucleus of an atom) ; 1 2(d) particle charge relative mass neutron 0 1 proton +1 1 ;; neutron row correct ; proton row correct ; 2 (a)(i) To earn these marks, you must define 'insoluble' as something that cannot or does not dissolve, and 'compound' as two or more elements chemically combined. (a)(ii) You need to describe three steps from filtering the insoluble solid, evaporating/heating the solution, allowing it to cool and crystallise, and then filtering/drying the crystals. (b) To earn these marks, you must state that water has two bond pairs and two lone pairs on the oxygen atom. (c) The mark is earned by defining mass number as the total number of protons and neutrons in the nucleus of an atom. (d) You must correctly fill in the charge and relative mass for both neutron and proton to earn the marks, with one mark for each correct row.

2 (a) Fig. 2.1 shows a process used to separate substances in a fossil fuel. fossil fuel Fig. 2.1 (i) Name this process. … [1] (ii) Name the fossil fuel that is separated by this process. … [1] (b) Methane is the main constituent of another fossil fuel. (i) Name this fossil fuel. … [1] (ii) Complete Fig. 2.2 to show the dot-and-cross diagram of one molecule of methane, CH4. H H H H C Fig. 2.2 [2] (iii) Identify a greenhouse gas that is formed by the complete combustion of methane. … [1] (c) Carbon has atomic number 6 and mass number 12. Hydrogen has atomic number 1 and mass number 1. Complete Table 2.1 to show the number of protons and the number of neutrons in one atom of carbon and in one atom of hydrogen. Table 2.1 atom number of protons number of neutrons carbon hydrogen [2] [Total: 8]

2(a)(i) fractional distillation ; 1 2(a)(ii) petroleum ; 1 2(b)(i) natural gas ; 1 2(b)(ii) ;; four bonding pairs of electrons = 2 marks one bonding pair correct = 1 mark 2 2(b)(iii) carbon dioxide / CO2 ; 1 2(c) number of protons number of neturons carbon 6 6 hydrogen 1 0 carbon row correct ; hydrogen row correct ; 2

Cambridge IGCSE Combined Science · 0653

IGCSE Combined Science (0653) Atoms, elements and compounds past paper questions

Revise IGCSE Combined Science (0653) — Atoms, elements and compounds with real Cambridge past-paper questions grouped by topic, each shown with its marking scheme. Working one topic at a time targets exactly the skill each question tests.

366 free questions from 2016–2021, each with its marking scheme. Open the full topical bank to filter by subtopic, paper, and year.

Atoms, elements and compounds in IGCSE Combined Science 0653 exams, 2020–2025

Across 2020–2025, Atoms, elements and compounds accounted for 353 questions worth 1,454 marks in Cambridge IGCSE Combined Science (0653) papers.

By year
Year	Questions	Marks
2020	40	196
2021	58	253
2022	51	261
2023	76	274
2024	72	277
2025	56	193

Most-tested subtopics

C2.4 Simple molecules and covalent bonds582 marks
C2.3 Ions and ionic bonds541 marks
C2.2 Atomic structure and the Periodic Table441 marks

Appears in

Paper 1 · 100 qs
Paper 2 · 114 qs
Paper 3 · 70 qs
Paper 4 · 67 qs
Paper 5 · 1 q
Paper 6 · 1 q

All most-tested Combined Science topics

2021 Feb/Mar · Paper 3 · Q2 · 7 marks
Marking scheme
$Mark scheme: 2(a) coal ; 1 2(b) methane / CH4 ; 1 2(c)(i) fractional distillation ; 1 2(c)(ii) (for making) roads ; 1 2(d)(i) carbon…$ Get Steven’s plain-English explanation
2021 May/Jun · Paper 3 · Q2 · 10 marks
Marking scheme
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2021 May/Jun · Paper 3 · Q2 · 10 marks
Marking scheme
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2021 May/Jun · Paper 3 · Q2 · 8 marks
Marking scheme
$Mark scheme: 2(a)(i) fractional distillation ; 1 2(a)(ii) petroleum ; 1 2(b)(i) natural gas ; 1 2(b)(ii) ;; four bonding pairs of…$ $Mark scheme: 2(a)(i) fractional distillation ; 1 2(a)(ii) petroleum ; 1 2(b)(i) natural gas ; 1 2(b)(ii) ;; four bonding pairs of… (continued)$ Get Steven’s plain-English explanation
2021 Oct/Nov · Paper 1 · Q14 · 1 mark
Marking scheme
Mark scheme — 2021 Paper 1 Q14
Answer: C
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