AQA GCSE Chemistry 8462: A simple model of the atom, symbols, relative atomic mass, electronic charge and isotopes – 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 from your board or school.

These questions cover section 4.1.1 A simple model of the atom, symbols, relative atomic mass, electronic charge and isotopes of the AQA GCSE Chemistry (8462) specification, for teaching from September 2016 onwards and exams in 2018 onwards (version 1.1): spec points 4.1.1.1 to 4.1.1.7. This content is examined on Paper 1 at Foundation and Higher Tier. Question 4 uses content the specification marks (HT only) and is labelled (Higher). Use a periodic table for atomic numbers.

Learn the content first in the study guide and the revision notes. For questions on group trends and the periodic table, use the topic 4.1 practice questions; the questions below are different. The course hub is AQA GCSE Chemistry and the printable checklist lists every topic.

Questions

1. State what is meant by (a) an atom and (b) a compound. [2]

2. Name the compounds with these formulae.

(a) MgCl₂ [1] (b) K₂SO₄ [1] (c) CaCO₃ [1] (d) How many atoms are shown in the formula Ca(OH)₂? [1]

3. Balance these equations and write one new equation.

(a) __Li + __O₂ → __Li₂O [1] (b) __Al + __Cl₂ → __AlCl₃ [1] (c) Sodium reacts with water to form sodium hydroxide and hydrogen. Write the word equation and the balanced symbol equation. [3]

4. (Higher) Chlorine water is added to sodium bromide solution. Bromine and sodium chloride form.

(a) Write the ionic equation for the reaction. [2] (b) Write the half equation for bromide ions forming bromine. [2] (c) Write the half equation for a magnesium atom forming a magnesium ion, Mg²⁺. [1]

5. Classify each substance as an element, a compound or a mixture: air, sodium chloride, oxygen, sea water, carbon dioxide, copper. [3]

6. A student is given four separation tasks.

(a) Obtain pure water from water-based ink. Name the technique and explain how it works. [2] (b) Liquid A (boiling point 65 °C) and liquid B (boiling point 98 °C) mix completely. Name the technique that separates them and explain why it works. [2] (c) Describe how to obtain copper sulfate crystals from copper sulfate solution. [2] (d) Name the technique that shows whether a food colouring contains more than one dye. [1]

7. Models of the atom changed as new evidence was found.

(a) Give two differences between the plum pudding model and the nuclear model. [2] (b) Explain why the results of the alpha particle scattering experiment led to the plum pudding model being replaced. [3] (c) State how Niels Bohr adapted the nuclear model, and what James Chadwick’s work provided evidence for. [2]

8. The radius of an atom is about 0.1 nm.

(a) Write 0.1 nm in metres, in standard form. [1] (b) The radius of a nucleus is about 1 × 10⁻¹⁴ m. Calculate how many times larger the radius of the atom is than the radius of the nucleus. [2] (c) A museum builds a model atom with a radius of 5 m. Calculate the radius its nucleus should have, in mm. [2] (d) State where almost all the mass of an atom is found. [1]

9. Give the numbers of protons, neutrons and electrons in each particle.

(a) ²⁷₁₃Al³⁺ [1] (b) ³²₁₆S²⁻ [1] (c) ³⁹₁₉K⁺ [1] (d) An atom has 12 protons and 13 neutrons. Identify the element and give its mass number. [1]

10. Lithium has two isotopes: lithium-6 (7.5%) and lithium-7 (92.5%).

(a) Give one similarity and one difference between atoms of the two isotopes. [2] (b) Calculate the relative atomic mass of lithium to 1 decimal place. [2] (c) Explain why the answer is closer to 7 than to 6. [1]

11. A sample of magnesium contains 79% magnesium-24, 10% magnesium-25 and 11% magnesium-26.

(a) Calculate the relative atomic mass of magnesium to 1 decimal place. [3] (b) Give the electronic structure of a magnesium atom and describe how it is drawn as a diagram. [2] (c) A magnesium-26 atom loses two electrons to form an ion. Give the numbers of protons, neutrons and electrons in the ion. [2] (d) Explain why magnesium-24 and magnesium-26 atoms have no overall charge. [1]

12. Electronic structures.

(a) Write the electronic structures of nitrogen, aluminium, argon and calcium. [4] (b) An atom has the electronic structure 2,8,6. Identify the element and explain how you decided. [2]

Answers

1. (a) The smallest part of an element that can exist [1]. (b) Two or more elements chemically combined in fixed proportions [1]. [2] Examiner insight: “Fixed proportions” and “chemically combined” are the creditworthy words; “two things mixed together” describes a mixture and scores nothing.

2. (a) Magnesium chloride [1] (b) Potassium sulfate [1] (c) Calcium carbonate [1] (d) 1 + 2 + 2 = 5 atoms [1] Examiner insight: Spelling of “sulfate” and “chloride” must be clear enough to be unambiguous; “chlorine” for chloride is a different substance and is not credited.

3. (a) 4Li + O₂ → 2Li₂O [1] (b) 2Al + 3Cl₂ → 2AlCl₃ [1] (c) sodium + water → sodium hydroxide + hydrogen [1]; correct formulae Na, H₂O, NaOH, H₂ [1]; 2Na + 2H₂O → 2NaOH + H₂ [1] Examiner insight: The balancing mark depends on correct formulae; changing H₂O to H₂O₂ to “make it balance” loses both the formula and balancing marks.

4. (a) Cl₂ and Br⁻ on the left, Cl⁻ and Br₂ on the right, with Na⁺ omitted [1]; Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂ [1] (b) Correct species, 2Br⁻ → Br₂ [1]; electrons on the correct side: 2Br⁻ → Br₂ + 2e⁻ [1] (c) Mg → Mg²⁺ + 2e⁻ [1] Examiner insight: Check charge as well as atoms: in (b) the left side is 2-, so the right must also be 2-, which only works with 2e⁻ on the right.

5. Elements: oxygen and copper [1]. Compounds: sodium chloride and carbon dioxide [1]. Mixtures: air and sea water [1]. [3] Examiner insight: Each mark needs both substances in that category correct, so one misplaced substance can cost two marks.

6. (a) Simple distillation [1]; water boils, the vapour is condensed and collected, and the dyes stay in the flask [1]. (b) Fractional distillation [1]; the liquids have different boiling points, so A (lower boiling point) reaches the top of the column and condenses first [1]. (c) Heat the solution to evaporate some water until it is saturated [1]; leave to cool so crystals form, then filter and dry them [1]. (d) Chromatography [1] Examiner insight: In (a) and (b) the technique name earns one mark and the explanation the other; a bare technique name scores half.

7. (a) Any two differences, one mark each [1] [1]: positive charge spread through the atom vs concentrated in a nucleus; mass spread out vs almost all in the nucleus; electrons embedded in the positive ball vs outside the nucleus; no empty space vs mostly empty space. (b) Some alpha particles were deflected through large angles [1]; a spread-out positive charge could not do this, so the plum pudding model could not explain the evidence [1]; the results showed mass and positive charge concentrated in a small nucleus, so the nuclear model replaced it [1]. (c) Bohr: electrons orbit the nucleus at specific distances [1]. Chadwick: the existence of neutrons in the nucleus [1]. Examiner insight: A “difference” mark needs both sides of the comparison; “the nuclear model has a nucleus” alone states one model, not a difference.

8. (a) 1 × 10⁻¹⁰ m [1] (b) (1 × 10⁻¹⁰) ÷ (1 × 10⁻¹⁴) [1] = 10 000 (1 × 10⁴) times [1] (c) 5 ÷ 10 000 = 0.0005 m [1] = 0.5 mm [1] (d) In the nucleus [1] Examiner insight: In (c) the unit conversion carries the second mark; 0.0005 left in metres when mm were asked for scores the method mark only.

9. (a) 13 protons, 14 neutrons, 10 electrons [1] (b) 16 protons, 16 neutrons, 18 electrons [1] (c) 19 protons, 20 neutrons, 18 electrons [1] (d) Magnesium, mass number 25 [1] Examiner insight: Each mark needs all three numbers right; the electron count for an ion is where the mark is usually dropped.

10. (a) Similarity: same number of protons (3) or electrons [1]. Difference: lithium-7 has one more neutron (4 compared with 3) [1]. (b) (6 × 7.5 + 7 × 92.5) ÷ 100 [1] = 6.925 = 6.9 [1] (c) Lithium-7 is far more abundant, so it contributes more to the average [1]. Examiner insight: A correct answer with no working still scores both marks in (b), but a wrong answer with no working scores zero; showing the expression protects the method mark.

11. (a) (24 × 79 + 25 × 10 + 26 × 11) ÷ 100 [1] = (1896 + 250 + 286) ÷ 100 = 24.32 [1] = 24.3 [1] (b) 2,8,2 [1]; a nucleus with three shells drawn round it, carrying 2, 8 and 2 electrons from the inside out [1] (c) 12 protons and 14 neutrons [1]; 10 electrons [1] (d) Each atom has equal numbers of protons and electrons (12 each), so the charges cancel [1]. Examiner insight: In (a) the abundance-weighted expression earns the method mark even if the arithmetic slips; the final mark needs the 1 d.p. answer asked for.

12. (a) Nitrogen 2,5 [1]; aluminium 2,8,3 [1]; argon 2,8,8 [1]; calcium 2,8,8,2 [1] (b) 2 + 8 + 6 = 16 electrons, so atomic number 16 [1]; the element is sulfur [1]. Examiner insight: For (b) the reasoning mark needs the link from electron total to atomic number; naming sulfur with no reason scores one mark.

Where marks are usually lost

• Counting atoms in a formula with brackets without multiplying everything inside the bracket.
• Changing a formula, rather than the number in front, to balance an equation.
• (Higher) Half equations with the electrons on the wrong side or with unbalanced charge.
• Calling air or sea water a compound: their parts are not chemically combined.
• Naming a separation technique but not saying which property it relies on.
• Comparing atomic models by describing only one model.
• Saying the scattering experiment showed electron shells: that was Bohr’s adaptation.
• Leaving a converted length in metres when the question asks for millimetres.
• Adding electrons to positive ions instead of removing them.
• Dropping the divide-by-100 step, or rounding before the final line, in relative atomic mass.

Next steps

• Recap with the revision notes.
• Reread any weak area in the study guide.
• Practise the rest of topic 4.1 with the topic 4.1 practice questions.
• Go back to the AQA GCSE Chemistry hub or the printable checklist.
• Try one of the free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

AQA GCSE Chemistry (8462) specification, for teaching from September 2016, exams from June 2018 (version 1.1), published by AQA: section 4.1.1, A simple model of the atom, symbols, relative atomic mass, electronic charge and isotopes.