Atoms, elements and compounds — IGCSE Science - Combined (0653) questions by topic
Atomic structure, electron-shell diagrams and distinguishing elements from compounds and mixtures define this topic: working out atomic and mass numbers from given electron and neutron counts, completing an electron diagram for a chlorine atom, and identifying diagrams showing mixtures of elements. State, identify and complete lead the command words, and complete wants every electron placed in the correct shell rather than just the right total.
With 11 real questions from 2023 to 2025 papers and marks from 1 to 11, single-value recall sits beside diagram-completion tasks. Submitting each diagram and short answer for instant marking is useful here, since it catches quickly when only outer-shell electrons should be drawn but the full quota is given instead.
What examiners look for
- A recurring slip uses the word particle instead of atoms when describing how elements are joined in a compound.
- Explanations often omit that atoms in a compound are combined chemically, not just physically mixed.
- Chemical formulae must be given in symbol form; answers given only in words are not accepted.
- Electron-shell diagrams are marked down when the full quota of electrons is shown rather than only those in the outer shell.
- Strong answers state that bacteria are killed by chlorine, and correctly explain that neon is unreactive because it has a full outer shell of electrons.
May–June 2025, Paper 11
Which diagram represents a mixture of two different elements? Each diagram is a box containing circular particles, some open (white) and some filled (black). A mixture of two…
Answer this question and get it marked →May–June 2025, Paper 12
Which statement describes how an atom forms an ion with a 1+ charge? A The atom gains 1 electron. B The atom gains 7 electrons. C The atom loses 1 electron. D The atom loses 7…
Answer this question and get it marked →Which molecule contains the lowest number of outer-shell electrons? A Cl2 B CH4 C H2 D H2O
Answer this question and get it marked →May–June 2025, Paper 21
Which diagram represents a mixture of elements? A particles each made of two identical (open) atoms joined together, all the same kind B a mixture of different molecules,…
Answer this question and get it marked →A neutral atom of chlorine contains 17 electrons and 18 neutrons. What is the atomic number and what is the mass number of this atom? atomic number mass number --- --- --- A 17 35…
Answer this question and get it marked →May–June 2025, Paper 23
Which diagram represents molecules of a single compound? Each option shows a box containing particles drawn as open (white) circles and filled (black) circles bonded together. A…
Answer this question and get it marked →May–June 2025, Paper 33
Lithium fluoride, LiF, is an ionic compound. Complete the sentences to explain why lithium fluoride has a high melting point. Choose words from the list. Each word may be used…
Answer this question and get it marked →May–June 2024, Paper 31
The elements chlorine, bromine and iodine are diatomic covalent molecules. State the meaning of diatomic.
Answer this question and get it marked →October–November 2023, Paper 31
Chlorine is in Group VII of the Periodic Table. A chlorine atom has 17 electrons and nucleon number 35. Complete Fig. 8.1 to show the electrons in this chlorine atom.
Answer this question and get it marked →October–November 2023, Paper 32
Chlorine exists as diatomic molecules. State what is meant by the term molecule.
Answer this question and get it marked →October–November 2023, Paper 33
Chlorine exists as diatomic molecules. State what is meant by the term molecule.
Answer this question and get it marked →Other IGCSE Science - Combined topics
- Practical skills (96)
- Motion, forces and energy (53)
- Electricity and magnetism (38)
- Waves (32)
- Human nutrition (23)
- Acids, bases and salts (22)
- Organisms and their environment (21)
- Organic chemistry (21)
- Reproduction (20)
- Thermal physics (20)
- Plant nutrition (19)
- The Periodic Table (18)