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

These are original questions written for Marlbridge, in the style and at the standard of the examination. They are not reproduced past-paper questions — 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. Questions 1, 2 and 4 test C1.2 Atomic structure (Papers 1 and 3); questions 3 and 5-11 test C4.1 Predicting chemical reactions – group trends and the periodic table (Papers 2 and 4). Use the two halves alongside the paper they actually belong to rather than as a single Paper 1/3 set.

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Section A

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

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

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

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Section B

4. 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]

5. 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]

6. 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]

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

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

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

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

11. 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. Proton: mass 1, charge +1 [1]. Neutron: mass 1, charge 0 [1]. Electron: mass very small (1/1836), charge −1 [1].

2. 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].

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

4. (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].

5. (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.

6. (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].

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

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

9. 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].

10. 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].

11. 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.