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Electron structure and orbitals

Past-paper questions pack

Name
Class
Date set
Date due
Score/ 45

Questions are numbered; the mark schemes (the answer key) follow on separate pages so the question pages can be handed out alone. www.chemistryaleveltutor.com

OCR AS and A-level Chemistry past-paper questions since 2016 · 32 parts · mark schemes follow the questions · www.chemistryaleveltutor.com · Questions and mark schemes © OCR

1. June 2025 · AS Paper 1 · Q2 · 1 marks ·
2 How many p electrons does an atom of chlorine have? A 5 B 7 C 11 D 17 Your answer [1]
2. June 2024 · AS Paper 1 · Q1 · 1 marks ·
1 Which diagram shows a p‑orbital? A B C D Your answer [1]
3. June 2024 · Paper 1 · Q1 · 1 marks ·
1 Oxygen has the electron configuration 1s22s22p4. How are the electrons in an atom of oxygen arranged in the p-orbitals? A ↑↑ ↑↑ B ↑↓ ↑↓ C ↑↑ ↑ ↑ D ↑↓ ↑ ↑ Your answer [1]
4. June 2024 · Paper 1 · Q22(a) · 2 marks ·
22 This question is about transition elements. (a) Iron is in the d block of the periodic table and contains s, p and d orbitals. • Draw diagrams to show the shapes of an s orbital and a p orbital. • Complete the electron configurations of an iron atom and an iron(II) ion. Shapes s orbital p orbital Electron configurations Iron atom: 1s2 ................................................................................................................................... Iron(II) ion 1s2 .................................................................................................................................. [2]
5. June 2024 · AS Paper 2 · Q2(a)(i) · 3 marks ·
2 This question is about periodicity and the reaction of some Group 2 metals. (a) Periodicity is the repeating trend in properties of elements across different periods in the periodic table. (i) Complete the table below with the electron configurations and blocks. Group 2 Group 17 (7) Period 2 Be F 1s2 ........................................................ 1s2 ........................................................ Period 3 Mg Cl 1s2 ........................................................ 1s2 ........................................................ Block ............................. ............................. [3]
6. June 2023 · AS Paper 1 · Q4 · 1 marks · AO1
4 How many p-orbitals are occupied by electrons in a sulfur atom? A 2 B 4 C 6 D 10 Your answer [1]
7. June 2023 · Paper 1 · Q22(a) · 6 marks · AO1
22 This question is about the d-block elements in Period 4 of the periodic table (Sc to Zn). (a)* Explain, with examples from Period 4, what is meant by the terms d-block element and transition element. Explain why some d-block elements are not transition elements. Use electron configurations to support your explanations. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [6] Additional answer space if required. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ...................................................................................................................................................
8. June 2023 · AS Paper 2 · Q1(a)(ii) · 1 marks · AO1
(ii) Complete the electron configuration of a titanium atom. 1s2 ................................................................................................................................ [1]
9. June 2023 · Paper 3 · Q1(d) · 2 marks · AO1
(d) The two elements with atoms containing five unpaired electrons. ....................................... [2]
10. June 2022 · AS Paper 1 · Q4 · 1 marks · AO2
4 What is the number of paired orbitals in a sulfur atom? A 4 B 6 C 7 D 8 Your answer [1]
11. June 2022 · Paper 1 · Q15 · 1 marks · AO1
15 Which ion(s) contain(s) one or more unpaired electrons? 1 Mn3+ 2 V3+ 3 Cu+ A 1, 2 and 3 B Only 1 and 2 C Only 2 and 3 D Only 1 Your answer [1]
12. June 2022 · AS Paper 1 · Q22(b) · 2 marks · AO1
(b) Complete the table for an atom and an ion of two different elements. Mass Element Protons Neutrons Electron configuration Charge number 28 34 0 ................... ................... ................................................. 33 1s22s22p63s23p6 3– ................... ................... ................... [2]
13. November 2021 · AS Paper 1 · Q9 · 1 marks · AO1
9 Which element has atoms with the largest number of unpaired p-electrons? A aluminium B oxygen C chlorine D phosphorus Your answer [1]
14. November 2021 · Paper 1 · Q16(b)(iii) · 1 marks · AO2
(iii) Electrons occupy orbitals. In Table 16.2 below, add a tick (✓) below the ionisation numbers that are responsible for removing an electron from a full orbital in a magnesium atom. Ionisation 1 2 3 4 5 6 7 8 9 10 11 12 number Table 16.2 [1]
15. November 2021 · AS Paper 1 · Q21(a) · 2 marks · AO1
SECTION B Answer all the questions. 21 This question is about atomic structure. (a) Complete the table to show the maximum number of electrons that can occupy each shell and sub-shell. Some boxes may need to be left blank. Sub-shell Total number Shell of electrons s p d 1st 2nd 3rd [2]
16. November 2021 · AS Paper 2 · Q5(d)(ii) · 1 marks · AO1
(ii) Complete the electron configuration of gallium. 1s2 ................................................................................................................................ [1]
17. November 2020 · AS Paper 1 · Q5 · 1 marks · AO2
5 Which p-block element contains atoms with one unpaired electron? A Al B Si C P D S Your answer [1]
18. November 2020 · Paper 1 · Q14 · 1 marks · AO1
14 Which statement(s) for Group 2 elements is/are correct? 1 The 2nd ionisation energy of magnesium is greater than the 2nd ionisation energy of calcium. 2 A strontium ion, Sr2+, contains a total of 6 electrons in s orbitals. 3 The equation for the reaction of barium with water is: 2Ba + 2H2O 2BaOH + H2. A 1, 2 and 3 B Only 1 and 2 C Only 2 and 3 D Only 1 Your answer [1]
19. November 2020 · AS Paper 1 · Q21(a) · 1 marks · AO1
SECTION B Answer all the questions. 21 This question is about atoms, isotopes and mass spectrometry. (a) Complete the table to show the number of electrons that can fill the first four shells. Shell 1st shell 2nd shell 3rd shell 4th shell Number of electrons [1]
20. November 2020 · AS Paper 1 · Q22(a)(i) · 1 marks · AO1
22 This question is about compounds of bromine. (a) Bromine reacts with phosphorus, P4, to form phosphorus tribromide, PBr3. (i) Complete the electron configuration of a bromine atom. 1s2 ................................................................................................................................ [1]
21. June 2019 · Paper 1 · Q1 · 1 marks · AO1
1 In the diagrams below, each box represents an orbital and each electron is shown as an arrow. Which diagram shows the correct arrangement of electrons in an atom of carbon? 2p 2s A energy 1s 2p 2s B energy 1s 2p 2s C energy 1s 2p 2s D energy 1s Your answer [1]
22. June 2019 · AS Paper 1 · Q21(c) · 2 marks · AO1
(c) Electrons occupy orbitals which are arranged in energy levels. In the diagram below, each box represents an orbital and each electron is shown as an arrow. Label the sub-shells and add arrows to show how electrons occupy orbitals in an atom of oxygen. .......... energy .......... 1 s .......... [2]
23. June 2018 · AS Paper 1 · Q1 · 1 marks ·
1 The electron configuration of element X is: 1s22s22p63s23p4 What is the formula of a compound formed when sodium reacts with element X? A NaX B NaX2 C Na2X D Na2X3 Your answer [1]
24. June 2018 · AS Paper 2 · Q2(c)(i) · 1 marks ·
(c) Selenium is in the same group of the periodic table as sulfur. (i) Complete the full electron configuration of a selenium atom. 1s2 ................................................................................................................................ [1]
25. June 2018 · Paper 3 · Q1(a)(i) · 1 marks ·
1 This question refers to the elements in the first three periods (H Ar) of the Periodic Table. (a) Select an element from the first three periods that fits each of the following descriptions. (i) The element that forms a 1– ion with the same electron configuration as helium. .............................. [1]
26. June 2017 · AS Paper 1 · Q6 · 1 marks ·
6 Which element has atoms with the greatest number of singly occupied orbitals? A C B Cl C Ca D Ga Your answer [1]
27. June 2017 · Paper 1 · Q15 · 1 marks ·
15 Which electron configuration(s) is/are correct? 1 Cr atom: 1s22s22p63s23p63d54s1 2 Cu atom: 1s22s22p63s23p63d104s1 3 Fe2+ ion: 1s22s22p63s23p63d54s1 A 1, 2 and 3 B Only 1 and 2 C Only 2 and 3 D Only 1 Your answer [1]
28. June 2017 · AS Paper 1 · Q22(c)(iv) · 2 marks ·
(iv) Explain why the general increase in first ionisation energies across Period 3 is not followed for Mg (Z = 12) to Al (Z = 13). ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]
29. June 2017 · AS Paper 2 · Q1(c)(i) · 1 marks ·
(c) Barium nitride is formed when barium is heated with nitrogen. (i) Complete the electron configuration of a nitride ion. 1s2 ................................................................................................................................. [1]
30. June 2016 · AS Paper 1 · Q6 · 1 marks ·
6 How many orbitals are occupied in a silicon atom? A 5 B 7 C 8 D 9 Your answer [1]
31. June 2016 · AS Paper 1 · Q23(a)(i) · 1 marks · AO1
17 23 This question is about properties of the halogens and halide ions. (a) Bromine can be extracted by bubbling chlorine gas through concentrated solutions containing bromide ions. (i) Write the electron configuration of a bromide ion, in terms of sub-shells. ...................................................................................................................................... [1]
32. June 2016 · AS Paper 2 · Q1(a)(i) · 1 marks · AO1
1 Group 2 elements are metals that react with oxygen and water. (a) Magnesium is oxidised when it burns in oxygen to form an ionic compound. (i) Write the electron configuration, in terms of sub-shells, of a magnesium atom. ...................................................................................................................................... [1]

Mark schemes

1. June 2025 · AS Paper 1 · Q2
Mark scheme June 2025 Paper 1 Q2
2. June 2024 · AS Paper 1 · Q1
Mark scheme June 2024 Paper 1 Q1
3. June 2024 · Paper 1 · Q1
Mark scheme June 2024 Paper 1 Q1
4. June 2024 · Paper 1 · Q22(a)
Mark scheme June 2024 Paper 1 Q22(a)
5. June 2024 · AS Paper 2 · Q2(a)(i)
Mark scheme June 2024 Paper 2 Q2(a)(i)
6. June 2023 · AS Paper 1 · Q4
Mark scheme June 2023 Paper 1 Q4
7. June 2023 · Paper 1 · Q22(a)
Mark scheme June 2023 Paper 1 Q22(a)
8. June 2023 · AS Paper 2 · Q1(a)(ii)
Mark scheme June 2023 Paper 2 Q1(a)(ii)
9. June 2023 · Paper 3 · Q1(d)
Mark scheme June 2023 Paper 3 Q1(d)
10. June 2022 · AS Paper 1 · Q4
Mark scheme June 2022 Paper 1 Q4
11. June 2022 · Paper 1 · Q15
Mark scheme June 2022 Paper 1 Q15
12. June 2022 · AS Paper 1 · Q22(b)
Mark scheme June 2022 Paper 1 Q22(b)
13. November 2021 · AS Paper 1 · Q9
Mark scheme November 2021 Paper 1 Q9
14. November 2021 · Paper 1 · Q16(b)(iii)
Mark scheme November 2021 Paper 1 Q16(b)(iii)
15. November 2021 · AS Paper 1 · Q21(a)
Mark scheme November 2021 Paper 1 Q21(a)
16. November 2021 · AS Paper 2 · Q5(d)(ii)
Mark scheme November 2021 Paper 2 Q5(d)(ii)
17. November 2020 · AS Paper 1 · Q5
Mark scheme November 2020 Paper 1 Q5
18. November 2020 · Paper 1 · Q14
Mark scheme November 2020 Paper 1 Q14
19. November 2020 · AS Paper 1 · Q21(a)
Mark scheme November 2020 Paper 1 Q21(a)
20. November 2020 · AS Paper 1 · Q22(a)(i)
Mark scheme November 2020 Paper 1 Q22(a)(i)
21. June 2019 · Paper 1 · Q1
Mark scheme June 2019 Paper 1 Q1
22. June 2019 · AS Paper 1 · Q21(c)
Mark scheme June 2019 Paper 1 Q21(c)
23. June 2018 · AS Paper 1 · Q1
Mark scheme June 2018 Paper 1 Q1
24. June 2018 · AS Paper 2 · Q2(c)(i)
Mark scheme June 2018 Paper 2 Q2(c)(i)
25. June 2018 · Paper 3 · Q1(a)(i)
Mark scheme June 2018 Paper 3 Q1(a)(i)
26. June 2017 · AS Paper 1 · Q6
Mark scheme June 2017 Paper 1 Q6
27. June 2017 · Paper 1 · Q15
Mark scheme June 2017 Paper 1 Q15
28. June 2017 · AS Paper 1 · Q22(c)(iv)
Mark scheme June 2017 Paper 1 Q22(c)(iv)
29. June 2017 · AS Paper 2 · Q1(c)(i)
Mark scheme June 2017 Paper 2 Q1(c)(i)
30. June 2016 · AS Paper 1 · Q6
Mark scheme June 2016 Paper 1 Q6
31. June 2016 · AS Paper 1 · Q23(a)(i)
Mark scheme June 2016 Paper 1 Q23(a)(i)
32. June 2016 · AS Paper 2 · Q1(a)(i)
Mark scheme June 2016 Paper 2 Q1(a)(i)