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Basic ideas about atoms: WJEC A‑Level Chemistry questions

Every WJEC A-Level Chemistry exam question on 1.2 Basic ideas about atoms, 2016–2025, with its mark scheme and examiner’s report.

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1,204 questions

  1. Q3

    Summer 2025 · AS Unit 1

    1 mark1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2025 AS Unit 1, question 3: The visible emission spectrum of hydrogen shows prominent lines at wavelengths of 434 nm, 486 nm and 656 nm. Complete the sentences by using the words higher or

  2. Q9(b)(i)

    Summer 2025 · AS Unit 1

    3 marks1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2025 AS Unit 1, question 9(b)(i): alpha emission and has a half-life of 3.8 days. Scientists are concerned about the build-up of 222Rn in homes since it may cause lung cancer. Explain why 222Rn

  3. Q9(b)(ii)

    Summer 2025 · AS Unit 1

    2 marks1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2025 AS Unit 1, question 9(b)(ii): α α 226Ra 222Rn 218Po 214Po Pb Bi Complete the series by labelling the last three arrows to indicate the nature of the radioactive decay occurring in each step.

  4. Q6(a)

    Summer 2024 · AS Unit 1

    1 mark1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2024 AS Unit 1, question 6(a): has twice the number of neutrons that there are in . [1] S O 16 8

  5. Q6(b)

    Summer 2024 · AS Unit 1

    1 mark1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2024 AS Unit 1, question 6(b): The sum of the number of electrons in and is equal to the number of O O 8 8 32 2– electrons in . [1] S 16

  6. Q10(a)(i)

    Summer 2024 · AS Unit 1

    2 marks1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2024 AS Unit 1, question 10(a)(i): Write an equation to show this decay. [2]

  7. Q10(a)(ii)

    Summer 2024 · AS Unit 1

    2 marks1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2024 AS Unit 1, question 10(a)(ii): Complete the graph below to show how the radioactivity of a sample of iodine-124 would vary with time. [2] 100 75 Radioactivity / 50 arbitrary units 25 0 0 4 8

  8. Q11(b)(ii)

    Summer 2024 · AS Unit 1

    4 marks1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2024 AS Unit 1, question 11(b)(ii): Calculate the value of the wavelength, in nm, of the radiation that corresponds to this energy change. [4] Wavelength = … …….. nm

  9. Q4(a)

    Summer 2023 · AS Unit 1

    1 mark1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2023 AS Unit 1, question 4(a): On the diagram, draw an arrow to represent the transition corresponding to the ionisation of the atom. Label this arrow A. [1]

  10. Q4(b)

    Summer 2023 · AS Unit 1

    1 mark1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2023 AS Unit 1, question 4(b): On the diagram, draw an arrow to represent the transition corresponding to the first line in the visible region in the atomic spectrum. Label this arrow B. [1]

  11. Q8(d)(i)

    Summer 2023 · AS Unit 1

    1 mark1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2023 AS Unit 1, question 8(d)(i): decays. [1]

  12. Q8(d)(ii)

    Summer 2023 · AS Unit 1

    2 marks1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2023 AS Unit 1, question 8(d)(ii): left after 2.88 × 106 years. [2] Mass = g

  13. Q6(a)

    Summer 2022 · AS Unit 1

    1 mark1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2022 AS Unit 1, question 6(a): Give the mass number and symbol of the element formed as a product of the radioactive decay of uranium-235. [1]

  14. Q6(b)

    Summer 2022 · AS Unit 1

    1 mark1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2022 AS Unit 1, question 6(b): fraction left =

  15. Q9(a)(i)

    Summer 2022 · AS Unit 1

    2 marks1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2022 AS Unit 1, question 9(a)(i): Explain the origins of emission spectra. [2]

  16. Q9(a)(ii)

    Summer 2022 · AS Unit 1

    1 mark1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2022 AS Unit 1, question 9(a)(ii): Give one difference in the appearance of absorption and emission spectra. [1]

  17. Q9(b)

    Summer 2022 · AS Unit 1

    2 marks1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2022 AS Unit 1, question 9(b): A line in the emission spectrum of an element has a wavelength of 95.0 nm. Calculate the frequency of this line in megahertz, MHz. [2] frequency = MHz

  18. Q9(c)(i)

    Summer 2019 · AS Unit 1

    1 mark1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2019 AS Unit 1, question 9(c)(i): Give the mass number and symbol of the element formed as a product of the radioactive decay of magnesium-28. [1]

  19. Q9(c)(ii)

    Summer 2019 · AS Unit 1

    1 mark1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2019 AS Unit 1, question 9(c)(ii): If it takes 84 hours for the activity of the isotope to decay to of its original 16 th activity, calculate its half-life. [1] Half-life = hours

  20. Q10(a)

    Summer 2019 · AS Unit 1

    2 marks1.2 Basic ideas about atoms
    The whole paper ↗
    Summer 2019 AS Unit 1, question 10(a): Describe the processes within a hydrogen atom that cause electromagnetic radiation to be emitted. [2]
All 35 questions on Basic ideas about atoms, as a list
  1. Summer 2025, AS Unit 1, Q3 (1 mark): The visible emission spectrum of hydrogen shows prominent lines at wavelengths of 434 nm, 486 nm and 656 nm. Complete the sentences by using the words higher or
  2. Summer 2025, AS Unit 1, Q9(b)(i) (3 marks): alpha emission and has a half-life of 3.8 days. Scientists are concerned about the build-up of 222Rn in homes since it may cause lung cancer. Explain why 222Rn
  3. Summer 2025, AS Unit 1, Q9(b)(ii) (2 marks): α α 226Ra 222Rn 218Po 214Po Pb Bi Complete the series by labelling the last three arrows to indicate the nature of the radioactive decay occurring in each step.
  4. Summer 2024, AS Unit 1, Q6(a) (1 mark): has twice the number of neutrons that there are in . [1] S O 16 8
  5. Summer 2024, AS Unit 1, Q6(b) (1 mark): The sum of the number of electrons in and is equal to the number of O O 8 8 32 2– electrons in . [1] S 16
  6. Summer 2024, AS Unit 1, Q10(a)(i) (2 marks): Write an equation to show this decay. [2]
  7. Summer 2024, AS Unit 1, Q10(a)(ii) (2 marks): Complete the graph below to show how the radioactivity of a sample of iodine-124 would vary with time. [2] 100 75 Radioactivity / 50 arbitrary units 25 0 0 4 8
  8. Summer 2024, AS Unit 1, Q11(b)(ii) (4 marks): Calculate the value of the wavelength, in nm, of the radiation that corresponds to this energy change. [4] Wavelength = … …….. nm
  9. Summer 2023, AS Unit 1, Q4(a) (1 mark): On the diagram, draw an arrow to represent the transition corresponding to the ionisation of the atom. Label this arrow A. [1]
  10. Summer 2023, AS Unit 1, Q4(b) (1 mark): On the diagram, draw an arrow to represent the transition corresponding to the first line in the visible region in the atomic spectrum. Label this arrow B. [1]
  11. Summer 2023, AS Unit 1, Q8(d)(i) (1 mark): decays. [1]
  12. Summer 2023, AS Unit 1, Q8(d)(ii) (2 marks): left after 2.88 × 106 years. [2] Mass = g
  13. Summer 2022, AS Unit 1, Q6(a) (1 mark): Give the mass number and symbol of the element formed as a product of the radioactive decay of uranium-235. [1]
  14. Summer 2022, AS Unit 1, Q6(b) (1 mark): fraction left =
  15. Summer 2022, AS Unit 1, Q9(a)(i) (2 marks): Explain the origins of emission spectra. [2]
  16. Summer 2022, AS Unit 1, Q9(a)(ii) (1 mark): Give one difference in the appearance of absorption and emission spectra. [1]
  17. Summer 2022, AS Unit 1, Q9(b) (2 marks): A line in the emission spectrum of an element has a wavelength of 95.0 nm. Calculate the frequency of this line in megahertz, MHz. [2] frequency = MHz
  18. Summer 2019, AS Unit 1, Q9(c)(i) (1 mark): Give the mass number and symbol of the element formed as a product of the radioactive decay of magnesium-28. [1]
  19. Summer 2019, AS Unit 1, Q9(c)(ii) (1 mark): If it takes 84 hours for the activity of the isotope to decay to of its original 16 th activity, calculate its half-life. [1] Half-life = hours
  20. Summer 2019, AS Unit 1, Q10(a) (2 marks): Describe the processes within a hydrogen atom that cause electromagnetic radiation to be emitted. [2]
  21. Summer 2019, AS Unit 1, Q10(b)(i) (1 mark): Explain why there are several series of lines. [1]
  22. Summer 2019, AS Unit 1, Q10(b)(ii) (1 mark): Explain why the lines within each series converge. [1]
  23. Summer 2019, AS Unit 1, Q10(c)(i) (1 mark): State what the limit represents. [1]
  24. Summer 2019, AS Unit 1, Q10(c)(ii) (4 marks): [4] Energy = kJ mol−1
  25. Summer 2018, AS Unit 1, Q7(d) (3 marks): Although radiation from radioisotopes is harmful to health many beneficial uses of radioactivity have been found. The table below gives some information about f
  26. Summer 2018, AS Unit 1, Q8(a)(i) (1 mark): Use the letter A to label the line of longest wavelength on the diagram. [1]
  27. Summer 2018, AS Unit 1, Q8(a)(ii) (2 marks): Explain why hydrogen atoms emit only certain definite frequencies of visible light. [2]
  28. Summer 2018, AS Unit 1, Q8(b)(ii) (3 marks): Calculate the minimum frequency of radiation required to ionise a hydrogen atom in its ground state. [3] Frequency = s–1
  29. Summer 2017, AS Unit 1, Q4(a) (1 mark): Write an equation to show this decay. [1]
  30. Summer 2017, AS Unit 1, Q4(b) (1 mark): of 81Kr to decay to 0.25 g. Calculate its half-life. [1] Half-life = years
  31. Summer 2017, AS Unit 1, Q6(a)(i) (3 marks): In the Balmer series, when an electron returns from the third shell to the second shell, a red line is seen at a wavelength of 656 nm. Calculate the energy of t
  32. Summer 2017, AS Unit 1, Q6(a)(ii) (2 marks): Explain how the Lyman series can be used to calculate the ionisation energy of hydrogen. [2]
  33. Summer 2016, AS Unit 1, Q3(a) (1 mark): Give the atomic number, mass number and symbol of the nuclide produced when 1 atom of 15O decays by the emission of one positron. [1]
  34. Summer 2016, AS Unit 1, Q3(b) (1 mark): 10 minutes. [1]
  35. Summer 2016, AS Unit 1, Q12(b) (2 marks): Hydrogen chloride is a colourless gas that absorbs at 278 nm in the ultraviolet region of the electromagnetic spectrum. Use this information and the data sheet

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