AQA GCSE Physics 8463: Atomic structure – 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 4.4 Atomic structure (4.4.1 to 4.4.4) of the AQA GCSE Physics (8463) specification, Version 1.1 (30 September 2019), for teaching from September 2016 and exams from 2018 onwards. The topic is assessed on Paper 1, set at Foundation and Higher Tier. Parts 7(c) and 10(b) test the one point the specification marks (HT only) and are labelled Higher tier only. A calculator is allowed throughout.

Learn the content first in the Atomic structure study guide and the revision notes. The course hub is AQA GCSE Physics, and the printable checklist lists every point.

Questions

1. Describe the structure of an atom. Include the approximate radius of an atom and where most of its mass is. [3]

2. Potassium has atomic number 19. Two of its isotopes are potassium-39 and potassium-40.

(a) Give the number of protons, neutrons and electrons in an atom of each isotope. [3] (b) An atom of potassium-39 loses one outer electron. Give the number of electrons in the particle formed, and name the type of particle. [1] (c) Explain why potassium-39 and potassium-40 are atoms of the same element. [1]

3. Before the alpha particle scattering experiment, scientists used the plum pudding model of the atom. Describe the plum pudding model, and explain how the results of the alpha scattering experiment led to the nuclear model. [6]

4. An electron in an atom absorbs electromagnetic radiation. Describe what happens to the electron, and what happens when it later emits radiation. [2]

5.

(a) Name the type of nuclear radiation that is stopped by a sheet of paper. [1] (b) Name the most strongly ionising of alpha, beta and gamma. [1] (c) A factory makes thin card. A source is placed above the card and a detector below it. If the card gets thicker, the count-rate falls. Explain which type of radiation the source should emit. [3]

6. Write balanced nuclear equations for these decays.

(a) Americium-241 (atomic number 95) emits an alpha particle and becomes neptunium. Neptunium has atomic number 93. [2] (b) Iodine-131 (atomic number 53) emits a beta particle and becomes xenon. Xenon has atomic number 54. [2]

7. A student measures the count-rate from a radioactive sample, corrected for background.

Time (min)	0	2	4	6	8
Count-rate (counts/s)	480	339	240	170	120

(a) Determine the half-life of the sample. Show how you used the data. [2] (b) Calculate the count-rate after 12 minutes. [2] (c) (Higher tier only) Calculate the net decline in count-rate after 20 minutes, as a ratio. [2] (d) Explain why the student cannot predict when a particular nucleus in the sample will decay. [1]

8. Compare the hazards of radioactive contamination and irradiation. [4]

9. In one area, a person’s yearly dose from background radiation is 2.7 mSv. A CT scan gives a dose of 8.1 mSv.

(a) Convert 2.7 mSv into sieverts. [1] (b) Calculate how many times greater the CT dose is than the yearly background dose. [1] (c) Give one natural and one man-made source of background radiation. [2] (d) Suggest why an airline pilot may receive a higher background dose than an office worker. [1]

10. A hospital needs a radioactive tracer to explore a patient’s kidneys. The detector is outside the body.

Isotope	Radiation emitted	Half-life
A	Alpha	6 hours
B	Gamma	6 hours
C	Gamma	5 years
D	Beta	2 days

(a) Evaluate which isotope is the best choice. Give reasons for rejecting the others. [4] (b) (Higher tier only) Calculate the fraction of the tracer’s initial activity left after 24 hours. [2] (c) A patient is worried about the radiation dose from the test. Suggest why a doctor still recommends it. [2]

11. Uranium-235 is used in nuclear reactors.

(a) Describe what happens when a uranium-235 nucleus undergoes fission. [4] (b) Each fission in a sample releases 3 neutrons. Assume every released neutron causes another fission. One fission starts the process. Calculate the number of fissions in the fourth generation, and explain what this shows. [3] (c) Explain the difference between the chain reaction in a nuclear reactor and in a nuclear weapon. [2]

12. Compare nuclear fission and nuclear fusion. [4]

Answers

1. A positively charged nucleus containing protons and neutrons [1]; surrounded by negatively charged electrons at different distances (energy levels) [1]; radius about 1 × 10⁻¹⁰ m, with most of the mass in the nucleus [1] Examiner insight: “Electrons in the nucleus” contradicts the structure and cancels the mark for that point.

2. (a) Both: 19 protons and 19 electrons [1]; potassium-39: 39 − 19 = 20 neutrons [1]; potassium-40: 40 − 19 = 21 neutrons [1] (b) 18 electrons; a positive ion [1] (c) Both have 19 protons (the same atomic number) [1] Examiner insight: An isotope answer that says “different mass” without “different number of neutrons” does not earn the mark.

3. Plum pudding: a ball of positive charge [1]; with negative electrons embedded in it [1]; most alpha particles passed straight through, so most of the atom is empty space [1]; some were deflected, so the centre is charged (positive, repelling the alpha particles) [1]; a very few bounced back, so the mass is concentrated in a tiny centre [1]; the plum pudding model could not explain this, so it was replaced by the nuclear model with a small, dense, positive nucleus [1] Examiner insight: AQA marks 6-mark answers by level; top-level answers link each observation to its conclusion rather than listing observations alone.

4. It moves further from the nucleus, to a higher energy level [1]; when it emits radiation it moves closer to the nucleus, to a lower energy level [1] Examiner insight: “The electron gains energy” alone is not enough; the mark needs the change in distance or energy level.

5. (a) Alpha [1] (b) Alpha [1] (c) Beta [1]; alpha would be stopped completely by the card, so the count-rate would not change with thickness [1]; gamma would pass through almost unchanged, so small changes in thickness would not be detected [1] Examiner insight: Choosing beta scores only the first mark; the other two need reasons for rejecting alpha and gamma.

6. (a) ²⁴¹₉₅Am → ²³⁷₉₃Np + ⁴₂He: mass numbers 241 = 237 + 4 [1]; atomic numbers 95 = 93 + 2 [1] (b) ¹³¹₅₃I → ¹³¹₅₄Xe + ⁰₋₁e: mass numbers 131 = 131 + 0 [1]; atomic numbers 53 = 54 + (−1) [1] Examiner insight: The beta symbol must show 0 on top and −1 below; writing ⁰₁e loses the atomic-number mark.

7. (a) 480 counts/s falls to 240 counts/s [1]; in 4 minutes [1] (b) 12 ÷ 4 = 3 half-lives [1]; 480 → 240 → 120 → 60 counts/s [1] (c) 20 ÷ 4 = 5 half-lives [1]; net decline = 1 : 32 (count-rate is 1/32 of the start, 15 counts/s) [1] (d) Radioactive decay is random [1] Examiner insight: In (a), a bare “4 minutes” with no halving shown can lose the method mark when the question says “show how”.

8. Contamination: radioactive atoms are on or in the object [1]; the hazard continues as long as those atoms keep decaying, and depends on the type of radiation [1]; irradiation: the object is only exposed to radiation from an outside source [1]; it does not become radioactive, so the hazard stops when the source is removed or shielded [1] Examiner insight: “Compare” needs both sides; four facts about contamination alone cap the answer at two marks.

9. (a) 2.7 ÷ 1000 = 0.0027 Sv [1] (b) 8.1 ÷ 2.7 = 3 times [1] (c) Natural: rocks or cosmic rays [1]; man-made: fallout from nuclear weapons testing or nuclear accidents [1] (d) Pilots fly at high altitude, where they are exposed to more cosmic rays [1] Examiner insight: Part (c) needs one source of each kind; two natural sources earn only one of the two marks.

10. (a) B [1]; gamma passes out of the body to the detector and is the least ionising, so it causes least damage [1]; a 6-hour half-life lasts long enough for the test but the activity falls quickly afterwards [1]; A’s alpha cannot leave the body and is strongly ionising; C stays active for years; D’s beta is more ionising and may not all reach the detector [1] (b) 24 ÷ 6 = 4 half-lives [1]; fraction left = 1/16 [1] (c) The benefit of diagnosing the illness is greater than the small risk from the dose [1]; the tracer’s short half-life means it does not stay highly active in the body for long [1] Examiner insight: “Evaluate” needs a clear choice plus reasons for rejecting the other options; a choice with no comparison stays in the lowest mark band.

11. (a) The nucleus absorbs a neutron [1]; it splits into two smaller nuclei of roughly equal size [1]; it emits two or three neutrons and gamma rays [1]; energy is released and all the fission products have kinetic energy [1] (b) Each generation is 3 times the one before: 1 → 3 → 9 → 27 [1]; fourth generation = 27 fissions [1]; the number of fissions grows very rapidly, so the energy released grows rapidly (a chain reaction) [1] (c) In a reactor the chain reaction is controlled, so energy is released at a controlled rate [1]; in a weapon it is uncontrolled, causing an explosion [1] Examiner insight: Missing “absorbs a neutron” as the first step is the usual gap in fission descriptions; spontaneous fission is rare.

12. Fission splits a large, unstable nucleus; fusion joins two light nuclei [1]; fission produces two smaller nuclei; fusion forms one heavier nucleus [1]; fission usually needs a neutron to be absorbed first; fusion does not [1]; both release energy (in fusion, some mass is converted into the energy of radiation) [1] Examiner insight: Each comparison mark needs both processes in the same point; separate paragraphs on each process rarely earn full credit.

Where marks are usually lost

• Linking “most alpha particles went straight through” to “the nucleus is small” instead of “the atom is mostly empty space”.
• Writing mass number as the number of neutrons.
• Giving the beta particle symbol with the wrong charge.
• Reading a half-life from a time value instead of from the drop to half the count-rate.
• Stopping one half-life short, or dividing the time by 2 instead of by the half-life.
• (Higher tier only) Writing the net decline as 1 : 10 after 5 half-lives, or giving a percentage when a ratio is asked for.
• Saying an irradiated object becomes radioactive.
• Choosing a source without saying why each other option is worse.
• Leaving out the neutron absorption, the extra neutrons or the gamma rays in a fission description.

Next steps

• Atomic structure revision notes
• Atomic structure study guide
• AQA GCSE Physics course hub
• Printable AQA GCSE Physics checklist
• All free 10-minute diagnostics
• Book a free trial class

Official syllabus

AQA GCSE Physics (8463) specification, Version 1.1, 30 September 2019, for teaching from September 2016 and exams from 2018 onwards (AQA), section 4.4 Atomic structure.