GCSE Chemistry: Atomic Structure and the Periodic Table — Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs — examination boards hold copyright in their own papers. Use these alongside the official past papers available free from your board.

Related: Atomic Structure revision notes

This paper spans two separate specification topics. In Section A, questions 1, 2 and 6-10 test C1.2 Atomic structure (Papers 1 and 3); questions 3-5 and 11-15 test C4.1 Predicting chemical reactions – group trends and the periodic table (Papers 2 and 4). In Section B, questions 16, 17 and 19 test atomic structure; questions 18 and 20-26 test group trends and the periodic table. Use the two halves alongside the paper they actually belong to rather than as a single Paper 1/3 set.

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OCR’s real J248 papers open with a whole-paper Section A of 15 multiple-choice questions (15 marks, four-option A-D) before a longer Section B of short-answer and extended questions. The set below now matches that real 15-mark weighting, but every question is drawn from the two topics covered in this file (atomic structure, and group trends in the periodic table) alone, rather than sampling across the whole specification as a genuine paper’s Section A would — so it is still not a reproduction of a full paper’s Section A.

Section A — Multiple choice (topic sample)

1. What is the relative charge of a neutron? A) +1 B) −1 C) 0 D) 2 [1]

2. Chlorine has two isotopes, ³⁵Cl and ³⁷Cl. Which statement correctly explains why the relative atomic mass of chlorine (35.5) is not a whole number? A) The mass number of an atom is always non-integer B) It is the weighted mean of the isotope masses, weighted by their relative abundance C) Neutrons have a slightly different mass to protons in this element D) The value includes the mass of the electrons, which reduces the whole-number total [1]

3. Which statement correctly explains why reactivity increases down Group 1? A) The atoms become smaller, so gain electrons more readily B) The number of protons decreases down the group, reducing nuclear attraction C) The outer electron is more strongly attracted to the nucleus, so is lost more easily D) The outer electron is further from the nucleus with more shielding, so is lost more easily [1]

4. Which statement correctly explains the trend in reactivity down Group 7? A) Reactivity decreases, because an incoming electron is attracted less strongly as shielding increases and the outer shell is further from the nucleus B) Reactivity increases, because the outer shell is further from the nucleus and gains an electron more easily C) Reactivity increases, because the atoms become smaller D) Reactivity decreases, because the outer electron is lost more easily further down the group [1]

5. An atom has the electron configuration 2,8,3. Which group and period is it in? A) Group 8, Period 3 B) Group 2, Period 8 C) Group 3, Period 3 D) Group 3, Period 2 [1]

6. The number of protons in a neutral atom is always equal to: A) The number of neutrons only B) The number of electrons C) The mass number D) The relative atomic mass [1]

7. What is the mass number of an atom? A) The number of protons only B) The number of protons plus the number of neutrons C) The number of protons plus the number of electrons D) The average mass of all isotopes of the element [1]

8. Which statement correctly defines isotopes? A) Atoms of different elements with the same mass number B) Atoms of the same element with the same number of protons but different numbers of neutrons C) Atoms of the same element with different numbers of protons D) Atoms with the same number of neutrons but different numbers of protons [1]

9. Which subatomic particle has a mass that is negligible compared with a proton or a neutron? A) Proton B) Neutron C) Electron D) All three have the same mass [1]

10. Where in an atom are the protons and neutrons located? A) In shells surrounding the nucleus B) In the nucleus C) Spread evenly throughout the atom D) Protons in the nucleus, neutrons in the shells [1]

11. On what basis did Mendeleev arrange elements in his early periodic table? A) Strictly increasing atomic number, with no exceptions B) Increasing relative atomic mass, sometimes leaving gaps and switching the strict mass order to keep elements with similar properties in the same group C) Alphabetical order of element names D) Date of discovery [1]

12. The modern periodic table arranges elements in order of: A) Increasing relative atomic mass, exactly as Mendeleev proposed B) Increasing atomic number (number of protons) C) Decreasing atomic number D) Alphabetical order [1]

13. How do the melting and boiling points of the Group 1 metals change down the group? A) They increase down the group B) They decrease down the group C) They stay the same for all Group 1 metals D) They increase and then decrease [1]

14. Which statement correctly describes the physical states of the Group 7 elements (halogens) at room temperature? A) All are gases B) Chlorine is a gas, bromine is a liquid, and iodine is a solid C) All are solids D) Chlorine is a solid, bromine is a gas, and iodine is a liquid [1]

15. Which group of the periodic table contains the noble gases, and what is their key chemical property? A) Group 1; highly reactive metals B) Group 7; reactive non-metals that readily form ions C) Group 0; very unreactive, because they have full outer electron shells D) Group 0; highly reactive, because of a single outer electron [1]

Section B — Short answer and extended questions

16. Give the relative mass and charge of a proton, a neutron and an electron. [3]

17. Explain why the relative atomic mass of chlorine is 35.5 and not a whole number. [2]

18. State why elements in the same group have similar chemical properties. [2]

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19. In the alpha-scattering experiment, alpha particles were fired at a thin gold foil.

(a) State three observations and the conclusion drawn from each. [6]

(b) Explain why this experiment led to the plum pudding model being replaced. [2]

20. Lithium, sodium and potassium all react with water.

(a) Write a word equation for the reaction of sodium with water. [1]

(b) State how the reactivity changes down the group. [1]

(c) Explain this trend fully. [3]

21. Chlorine, bromine and iodine are halogens.

(a) State how reactivity changes down Group 7. [1]

(b) Explain why this trend is the opposite direction to Group 1. [3]

(c) Chlorine is bubbled through potassium bromide solution. Predict the observation and write a word equation. [2]

22. Explain why the noble gases are unreactive. [2]

23. Magnesium has the electron configuration 2,8,2. State its group and period number, explaining how you know. [2]

24. State how melting and boiling points change down Group 7, and explain why — despite this trend, reactivity changes in the opposite direction. [3]

25. Explain why Mendeleev’s periodic table is remembered as a major scientific achievement. [2]

26. State the general rule for a halogen displacement reaction, and predict whether iodine will displace chlorine from potassium chloride solution, giving a reason. [2]

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Answers

1. C) A neutron carries no charge; it is protons that carry +1 and electrons that carry −1 [1].

2. B) Relative atomic mass is the weighted mean of the masses of an element’s isotopes, weighted by their relative abundance — it is not a simple average of the mass numbers, which is why it need not be a whole number [1].

3. D) Down Group 1 the outer electron is in a shell further from the nucleus with more shielding from inner shells, so it is attracted less strongly and lost more easily, making the atom more reactive [1].

4. A) Down Group 7 a halogen must gain an electron to react; as the outer shell gets further from the nucleus and shielding increases, an incoming electron is attracted less strongly, so reactivity decreases [1].

5. C) The number of outer-shell electrons (3) gives the group number, and the number of occupied shells (2,8,3 = three shells) gives the period number [1].

6. B) In a neutral atom, the number of protons (positive charge) is always balanced by an equal number of electrons (negative charge), so the atom has no overall charge [1].

7. B) Mass number is the total count of protons and neutrons in the nucleus; it does not include electrons, whose mass is negligible, and it is a whole-number count for a single atom, not an average [1].

8. B) Isotopes are atoms of the same element — so they have the same number of protons and the same atomic number — but with different numbers of neutrons, giving them different mass numbers [1].

9. C) An electron has a mass roughly 1/1840 that of a proton or neutron, which is treated as negligible on the relative mass scale used at this level [1].

10. B) The nucleus, at the centre of the atom, contains the protons and neutrons; electrons occupy shells around the nucleus [1].

11. B) Mendeleev arranged known elements mainly by increasing relative atomic mass, but left gaps for undiscovered elements and occasionally switched the strict mass order where needed to keep elements with similar chemical properties in the same group [1].

12. B) The modern periodic table is arranged by increasing atomic number (number of protons), which resolved the few ordering problems left by using relative atomic mass alone [1].

13. B) Melting and boiling points decrease down Group 1: caesium and francium, near the bottom, are the least stable of the Group 1 metals in this respect and have the lowest melting points [1].

14. B) At room temperature, chlorine is a pale green gas, bromine is a dense red-brown liquid, and iodine is a dark grey/purple solid — physical state changes from gas to liquid to solid down the group [1].

15. C) The noble gases are in Group 0 and are very unreactive because their atoms already have full outer electron shells, giving them no tendency to lose, gain or share electrons [1].

16. Proton: mass 1, charge +1 [1]. Neutron: mass 1, charge 0 [1]. Electron: mass very small (1/1840), charge −1 [1].

17. Chlorine exists as two isotopes (Cl-35 and Cl-37) [1], and the relative atomic mass is the weighted average of their masses allowing for abundance [1].

18. They have the same number of electrons in their outer shell [1], and it is the outer electrons that determine chemical behaviour [1].

19. (a) Most passed straight through [1] — the atom is mostly empty space [1]. Some were deflected [1] — the nucleus is positively charged (repelling the positive alpha particles) [1]. A very few bounced back [1] — the nucleus is very small but contains most of the mass [1].

(b) The plum pudding model predicted all particles would pass through with little deflection [1], because charge and mass were spread evenly — the observations could not be explained by it [1].

20. (a) sodium + water → sodium hydroxide + hydrogen [1].

(b) Reactivity increases down the group [1].

(c) The outer electron is in a shell further from the nucleus [1]; there is more shielding by inner shells [1]; so the attraction between the nucleus and the outer electron is weaker and the electron is lost more easily [1]. All three parts are required — most answers give only one.

21. (a) Reactivity decreases down Group 7 [1].

(b) A halogen must gain an electron rather than lose one [1]. Further down the group the outer shell is further from the nucleus with more shielding [1], so an incoming electron is attracted less strongly and is gained less readily [1].

(c) The solution turns orange/brown [1]. chlorine + potassium bromide → potassium chloride + bromine [1].

22. They have full outer electron shells [1], so they have no tendency to lose, gain or share electrons [1]. Not “because they are gases”.

23. Group 2 — the number of outer-shell electrons (2) [1]; Period 3 — the number of occupied shells (2,8,2 = three shells) [1].

24. Melting and boiling points increase down Group 7, because the molecules get larger and intermolecular forces strengthen [1]. Reactivity instead decreases, because a halogen must gain an electron, and further down the group the outer shell is further from the nucleus with more shielding, so an incoming electron is attracted less strongly [1] — melting/boiling point and reactivity are governed by two entirely different factors [1].

25. He left gaps for undiscovered elements and correctly predicted their properties [1]; the later discovery of gallium and germanium, matching his predictions, confirmed his table was correct [1].

26. A more reactive halogen displaces a less reactive one from its salt solution [1]. Iodine will not displace chlorine, since iodine is less reactive than chlorine (Group 7 reactivity decreases down the group, so iodine is the least reactive of the three) [1].

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Where marks are usually lost

• Giving the alpha-scattering observations without the conclusions.
• Saying reactivity increases down both Group 1 and Group 7.
• Giving only one reason for the Group 1 trend.
• Explaining noble gas unreactivity by their physical state.
• Forgetting that relative atomic mass is a weighted average.
• Confusing group number (outer-shell electrons) with period number (occupied shells).
• Assuming melting/boiling point and reactivity change in the same direction down Group 7 — they don’t.
• Predicting a less reactive halogen can displace a more reactive one — displacement only ever goes from more reactive to less reactive.