Paper 4 Atomic Structure Structured Practice
5 structured exam questions on atomic structure and bonding for IGCSE Chemistry Paper 4. Covers subatomic particles, electron configuration, isotopes, ionic and covalent bonding. Total: 26 marks.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
Five structured questions in the style of IGCSE Chemistry Paper 4, totalling 26 marks. Write your answers in full before checking the mark scheme.
Question 1 (5 marks)
The table shows information about four particles, P, Q, R, and S.
| Particle | Protons | Neutrons | Electrons |
|---|---|---|---|
| P | 11 | 12 | 11 |
| Q | 11 | 12 | 10 |
| R | 17 | 18 | 18 |
| S | 17 | 20 | 17 |
(a) Which particle is a positive ion? Explain your answer. [2]
(b) Which two particles are isotopes of the same element? Explain your answer. [2]
(c) State the electron configuration of particle S. [1]
Mark scheme
(a) Q is a positive ion [1]. It has more protons (11) than electrons (10), giving it a charge of +1 / it has lost one electron [1].
(b) R and S are isotopes [1]. They have the same number of protons (17) but different numbers of neutrons (18 and 20) / they are both chlorine but with different mass numbers [1].
(c) 2, 8, 7 [1]
Total: 5 marks
Question 2 (6 marks)
Sodium (atomic number 11) reacts with chlorine (atomic number 17) to form sodium chloride.
(a) State the electron configuration of a sodium atom and a chlorine atom. [2]
(b) Describe what happens to the electrons when sodium reacts with chlorine. [2]
(c) Explain why sodium chloride has a high melting point. [2]
Mark scheme
(a) Sodium: 2, 8, 1 [1]. Chlorine: 2, 8, 7 [1].
(b) The sodium atom transfers / loses its one outer electron to the chlorine atom [1]. Sodium becomes Na⁺ (2, 8) and chlorine becomes Cl⁻ (2, 8, 8) / both achieve stable noble gas electron configurations [1].
(c) Sodium chloride has a giant ionic lattice / structure [1]. There are strong electrostatic forces of attraction between the oppositely charged Na⁺ and Cl⁻ ions in all directions, which require a large amount of energy to overcome [1].
Total: 6 marks
Question 3 (5 marks)
Water (H₂O) has a low boiling point of 100 degC, while silicon dioxide (SiO₂) has a very high melting point of over 1700 degC. Both contain covalent bonds.
(a) Describe the bonding in a water molecule. [2]
(b) Explain, in terms of structure and bonding, why the boiling point of water is so much lower than the melting point of silicon dioxide. [3]
Mark scheme
(a) Each hydrogen atom shares one pair of electrons with the oxygen atom [1]. This is covalent bonding / a shared pair of electrons forms a covalent bond [1].
(b) Water consists of simple/discrete molecules with weak intermolecular forces between them [1]. Only these weak forces are broken during boiling, not the covalent bonds within the molecule [1]. Silicon dioxide has a giant covalent structure in which every atom is bonded to others by strong covalent bonds extending throughout the structure, and many strong bonds must be broken, requiring much more energy [1].
Total: 5 marks
Question 4 (5 marks)
Copper is a metal used for electrical wiring.
(a) Describe metallic bonding. [2]
(b) Explain why copper conducts electricity. [1]
(c) Explain why copper can be bent and shaped without breaking. [2]
Mark scheme
(a) Metal atoms lose their outer electrons to form positive ions [1]. The positive ions are held together by the electrostatic attraction between them and a sea of delocalised electrons [1].
(b) The delocalised electrons are free to move through the structure and carry the electrical charge/current [1].
(c) When a force is applied, layers of positive ions can slide over each other [1]. The metallic bonding is maintained because the delocalised electrons can shift to new positions / the sea of electrons holds the new arrangement together [1].
Total: 5 marks
Question 5 (5 marks)
Boron trichloride, BCl₃, and ammonia, NH₃, are both covalent compounds.
(a) State the number of covalent bonds formed by the boron atom in BCl₃. [1]
(b) State the number of covalent bonds formed by the nitrogen atom in NH₃. [1]
(c) Ammonia has a lone pair of electrons. Explain what a lone pair is. [1]
(d) When BCl₃ reacts with NH₃, a coordinate (dative covalent) bond forms. Explain what a coordinate bond is and why it forms in this reaction. [2]
Mark scheme
(a) 3 (three covalent bonds) [1]
(b) 3 (three covalent bonds) [1]
(c) A lone pair is a pair of electrons in the outer shell that is not involved in bonding / not shared with another atom [1].
(d) A coordinate bond is a covalent bond in which both electrons in the shared pair come from the same atom [1]. Nitrogen in NH₃ has a lone pair which it donates to the boron atom in BCl₃, which has an empty orbital / can accept a pair of electrons [1].
Total: 5 marks
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