![2 How many p electrons does an atom of chlorine have?
A 5
B 7
C 11
D 17
Your answer [1]](/img/JUN25_H0321/JUN25_H0321_02.webp)
Answer
C
Mark scheme
Examiner's comment
Most candidates answered this correctly, showing good knowledge of electron configuration.
Electron structure and orbitals Module 2
- Where it is examined
- A-level all three papers; AS Papers 1 and 2
- Level
- AS and A level
- Specification
- Section 2.2.1, 11 learning outcomes
- Since 2016
- 32 question parts: 14 multiple choice, 0 calculations, 1 six-mark level of response
Notes and key-term cards for this topic are being written by our tutors. The past-paper questions below are ready now.
Learning outcomes
Show the 11 learning outcomes from the specification
- 2.2.1(a) the number of electrons that can fill the first four shells
- 2.2.1(b) atomic orbitals, including:
- 2.2.1(b)(i) as a region around the nucleus that can hold up to two electrons, with opposite spins
- 2.2.1(b)(ii) the shapes of s- and p-orbitals
- 2.2.1(b)(iii) the number of orbitals making up s-, p- and d-sub-shells, and the number of electrons that can fill s-, p- and d-sub-shells
- 2.2.1(c) filling of orbitals:
- 2.2.1(c)(i) for the first three shells and the 4s and 4p orbitals in order of increasing energy
- 2.2.1(c)(ii) for orbitals with the same energy, occupation singly before pairing
- 2.2.1(d) deduction of the electron configurations of:
- 2.2.1(d)(i) atoms, given the atomic number, up to Z = 36
- 2.2.1(d)(ii) ions, given the atomic number and ionic charge, limited to s- and p-blocks up to Z = 36.
Six-mark level of response questions on this topic
| Series | Paper | Q | What it asks |
|---|---|---|---|
| June 2023 | Paper 1 | 22(a) | Explain, with examples from Period 4, what is meant by the terms d-block element and Explain why some d-block elements are not transition elements. |
Past-paper questions
Tap a question to zoom it. Where a part needs a table, graph or structure from an earlier part, that part folds out above it; the mark scheme and examiner's comment open underneath. Have the OCR Data Sheet beside you.
![1 Which diagram shows a p‑orbital?
A
B
C
D
Your answer [1]](/img/JUN24_H0321/JUN24_H0321_01.webp)
Answer
C
Mark scheme
Examiner's comment
Most candidates recognised C as a diagram for a p orbital.
![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]](/img/JUN24_H4321/JUN24_H4321_01.webp)
Answer
D
Mark scheme
Examiner's comment
The correct answer was D. Wrong answers were very rarely seen as candidates had secure knowledge of filling orbitals individually before pairing.
![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]](/img/JUN24_H4321/JUN24_H4321_22(a).webp)
Mark scheme
_MS.webp)
Examiner's comment
Many candidates were successful in drawing the orbital shapes. Occasionally candidates linked the question to the formation of a π bond or drew two arrows in a box to represent the electrons. Many candidates did not realise that when transition metal ions are formed, the first electrons removed from atoms are the 4s electrons and so wrote 2s2 2p6 3s2 3p6 3d4 4s2.
Notes from the mark scheme and report
- one p orbital only (DO NOT ALLOW several lobes)
- Fe2+ loses 4s electrons first
![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]](/img/JUN24_H0322/JUN24_H0322_02(a)(i).webp)
Mark scheme
(i)_MS.webp)
Examiner's comment
A very well answered question with most candidates very confident in giving the correct electron configurations and blocks. Errors were rare but included: 2p5 or 3p6 ending for Cl; using mass number for number of electrons; and assigning group 17 as d block and giving orbital box diagrams rather than block.
Notes from the mark scheme and report
- 1 mark per correct row
- blocks s and p
- IGNORE superscripts on block letter
![4 How many p-orbitals are occupied by electrons in a sulfur atom?
A 2
B 4
C 6
D 10
Your answer [1]](/img/JUN23_H0321/JUN23_H0321_04.webp)
Answer
C
Mark scheme
Examiner's comment
Candidates found this question more difficult than Questions 1–3. The question discriminated well. Most candidates showed the electron configuration in their working. A and D were the main distractors. Rather than the number of p-orbitals occupied, option A (2) is the number of p sub-shells (2p and 3p) and D (10) is the total number of p electrons (6 + 4). The errors may be the result of candidates not understanding the meaning of orbital and sub-shell or perhaps not reading the question closely enough. Underlining ‘p-orbitals’ may have helped candidates.
![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.
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Additional answer space if required.
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...................................................................................................................................................](/img/JUN23_H4321/JUN23_H4321_22(a).webp)
Mark scheme, with the levels and indicative points
_MS.webp)
Examiner's comment
Only the higher-attaining candidates scored full marks. Very few candidates were able to define d-block element correctly without the minor slip of saying outermost electron instead of highest energy or valence electron. Many candidates often did not mention ions for the transition metal definition. Many did not include any of the electron arrangements for d-block elements and transition elements. The majority of candidates who were able to recognise zinc and scandium as d-block elements, but not transition elements, gave their electronic configurations correctly. Common errors included the presence of the 4s electrons in the electron configurations of the ions and incorrect electron configurations of copper and chromium atoms. A few candidates thought chromium and copper were not transition elements due to the 4s1 electron configuration. This candidate has mentioned outer electrons rather than highest energy but was this is a minor slip and they were still given a Level 3 response as everything else is correct. A holistic approach for LoRs is used and not a point-based marking system.
Notes from the mark scheme and report
- d-block: highest energy electron in d sub-shell (DO NOT ALLOW d shell/d block)
- transition element forms an ion with incomplete d sub-shell
- Sc3+ (empty 3d) and Zn2+ (full 3d10) with configurations
![(ii) Complete the electron configuration of a titanium atom.
1s2 ................................................................................................................................ [1]](/img/JUN23_H0322/JUN23_H0322_01(a)(ii).webp)
Mark scheme
(ii)_MS.webp)
Examiner's comment
Again, most scored this mark. Common errors included using the mass number for number of electrons, no 4s but 3d4 instead, 4d rather than 3d, 4p2 instead of 3d2 or filling up d orbital 3d10.
Notes from the mark scheme and report
- 3d2 4s2 (ALLOW 4s before 3d)
- DO NOT ALLOW [Ar] shorthand
Earlier part of question 1 that this part uses
.webp)
![(d) The two elements with atoms containing five unpaired electrons.
....................................... [2]](/img/JUN23_H4323/JUN23_H4323_01(d).webp)
Mark scheme
_MS.webp)
Examiner's comment
Most candidates chose at least one of the two elements Cr and Mn, with Mn being the most common. Incorrect elements were usually other d block elements. Erratum
Notes from the mark scheme and report
- Cr (3d5 4s1) and Mn (3d5 4s2)
- IGNORE ions
![4 What is the number of paired orbitals in a sulfur atom?
A 4
B 6
C 7
D 8
Your answer [1]](/img/JUN22_H0321/JUN22_H0321_04.webp)
Answer
C
Mark scheme
Examiner's comment
This question was answered reasonably well. From the annotations on scripts many candidates wrote out the electron configuration of a sulfur atom. The successful candidates used electrons in a box notation so that they could visually see, and count, the paired orbitals. This is an excellent strategy to use in any similar questions.
![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]](/img/JUN22_H4321/JUN22_H4321_15.webp)
Answer
B
Mark scheme
Examiner's comment
This was another challenging question, with fewer candidates choosing the correct answer of B. Successful candidates often had the electronic configuration written down and focused on the higher energy electrons as to whether they were paired or not. Missing the 4s1 in Cu was the main omission to identify the correct answer. Section B overview
Notes from the mark scheme and report
- Cu+ is 3d10
![(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]](/img/JUN22_H0321/JUN22_H0321_22(b).webp)
Mark scheme
_MS.webp)
Examiner's comment
This question produced many mixed responses. Most candidates correctly identified nickel. However, its electron configuration was frequently shown as 3d10 instead of 3d8 and some less successful responses gave nickel’s relative atomic mass of 58.7 from the periodic table, instead of the mass number of the isotope provided. Many candidates selected the incorrect element for phosphorus, with argon being a key distractor from the extra 3 electrons in the P3– ion. The numbers of protons and neutrons were largely correct, although the wrong way round for many less successful responses.
Notes from the mark scheme and report
- marked by row
- ALLOW 4s2 before 3d8
- ALLOW P3–
![9 Which element has atoms with the largest number of unpaired p-electrons?
A aluminium
B oxygen
C chlorine
D phosphorus
Your answer [1]](/img/NOV21_H0321/NOV21_H0321_09.webp)
Answer
D
Mark scheme
Earlier part of question 16 that this part uses
(i).webp)
![(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]](/img/NOV21_H4321/NOV21_H4321_16(b)(iii).webp)
Mark scheme
(iii)_MS.webp)
Notes from the mark scheme and report
- 1st, 3rd, 4th, 5th, 9th and 11th only
![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]](/img/NOV21_H0321/NOV21_H0321_21(a).webp)
Mark scheme
_MS.webp)
Notes from the mark scheme and report
- first two rows correct 1 mark, third row 1 mark
- DO NOT ALLOW extra numbers
![(ii) Complete the electron configuration of gallium.
1s2 ................................................................................................................................ [1]](/img/NOV21_H0322/NOV21_H0322_05(d)(ii).webp)
Mark scheme
(ii)_MS.webp)
Notes from the mark scheme and report
- ALLOW 4s2 and/or 4p1 before 3d10
- DO NOT ALLOW [Ar] shorthand
![5 Which p-block element contains atoms with one unpaired electron?
A Al
B Si
C P
D S
Your answer [1]](/img/NOV20_H0321/NOV20_H0321_05.webp)
Answer
A
Mark scheme
Examiner's comment
Most candidates chose the correct response of A: Al. The best approach seen on many scripts was to write out the electron configuration beside the options and to count off the paired electrons.
![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]](/img/NOV20_H4321/NOV20_H4321_14.webp)
Answer
D
Mark scheme
Notes from the mark scheme and report
- Sr2+ has 8 s electrons
- Ba forms Ba(OH)2
![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]](/img/NOV20_H0321/NOV20_H0321_21(a).webp)
Mark scheme
_MS.webp)
Examiner's comment
21(a) Most candidates could recall the number of electrons in the first four shells as being 2, 8, 18 and 32. However, many made errors for the third and fourth shell. Common incorrect responses included 2,8,18,18 and 2,8,8,8, perhaps linking back to GCSE coverage. 2,6,10,14 was also seen, confusing shells with subshells. 21(b) Almost all candidates were aware that different isotopes had different numbers of neutrons. For the similarities, ‘the same number of protons’ was usually identified, but the same number electrons was omitted by many candidates. This suggested that candidates were concentrating on the nucleus and did not read the question closely enough which asked for ‘atomic’ structures. 21(c)(ii) This was a high demand question and only the highest scoring answers identified that the peak at 72 was caused by a chlorine molecule containing the chlorine-35 and chlorine-37 isotopes shown in the supplied mass spectrum. Very few candidates went on to predict further peaks with m/z values of 70 (from 35Cl35Cl) and 74 (from 37Cl37Cl). There was little pattern in the incorrect responses, suggestion that many were guesses.
Notes from the mark scheme and report
- all four numbers (2, 8, 18, 32) required
![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]](/img/NOV20_H0321/NOV20_H0321_22(a)(i).webp)
Mark scheme
(i)_MS.webp)
Examiner's comment
22(a)(i) Candidates answered this part well, showing good knowledge and understanding of electron configuration. When incorrect, it was usually errors with the number of electrons in the 3d and 4p subshells. 22a(ii) Most candidates were able to construct a correct balanced equation for this unfamiliar equation. The commonest error was use of Br instead of Br2 in the equation. 22(b) Structure and bonding continues to be a difficult concept for many candidates. This part did discriminate extremely well, with high-attaining candidates identifying that the compound would have a giant ionic lattice with fixed ions in the solid state which become mobile in the liquid state to conduct electricity. It was common for ‘ionic’ or ‘giant’ to be omitted in the name of the lattice. Most candidates used the ideal gas equation, which was usually rearranged correctly, with substituted values for p, V, R and T being added. A common mistake was for the volume in cm3 to be multiplied by 10–3 rather than 10–6 for the necessary conversion into m3. Low-attaining candidates often did not convert 100 ºC into 373 K. Unfortunately, candidates making an error in unit conversions then obtained an unrealistic molar mass for A and were then unable to derive a possible molecular formula. Well-prepared candidates carried out the calculation well with clear working. It was very encouraging to see the number of candidates able to predict the molecular formula of A as BrF5 from the calculated molar mass of 174.6 g mol–1. There were, however a significant number of incorrect responses, suggesting that some candidates found this type of question challenging. Some candidates used the molar gas volume at room temperature and pressure of 24.0 dm3 mol–1. Two of the five marks were still available for this response.
Notes from the mark scheme and report
- DO NOT ALLOW [Ar] shorthand
- ALLOW 3d after 4s2
- check 1s2 to 3p6 carefully for mistakes
![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]](/img/JUN19_H4321/JUN19_H4321_01.webp)
Answer
D
Mark scheme
![(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]](/img/JUN19_H0321/JUN19_H0321_21(c).webp)
Mark scheme
_MS.webp)
Examiner's comment
Most candidates added arrows correctly to the boxes but the sub-shell labels were sometimes omitted. Lower attaining candidates sometimes paired electrons, rather than showing them singly or showed six electrons in the 2p sub-shell. This suggested either a lack of understanding or failure to read the question.
Notes from the mark scheme and report
- 2s (single box) AND 2p (3 boxes) labelled
- 2p shown as one pair and two unpaired electrons
![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]](/img/JUN18_H0321/JUN18_H0321_01.webp)
Answer
C
Mark scheme
Examiner's comment
Nearly all candidates responded with the correct response of C.
![(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]](/img/JUN18_H0322/JUN18_H0322_02(c)(i).webp)
Mark scheme
(i)_MS.webp)
Examiner's comment
Most candidates answered this correctly. The most common error seen was 4p6 instead of 4p4
Notes from the mark scheme and report
- ALLOW 3d10 after 4s2 or 4p4
- DO NOT ALLOW [Ar] shorthand
![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]](/img/JUN18_H4323/JUN18_H4323_01(a)(i).webp)
Mark scheme
(i)_MS.webp)
Examiner's comment
Most candidates were credited this straightforward mark and identified that hydrogen would gain an electron to form a 1– ion. Some candidates opted for lithium, able to form an ion with the same electron configuration as helium, but with a 1+ rather than a 1– charge. Candidates are recommended to look closely at the requirements of the question set.
Notes from the mark scheme and report
- hydrogen (H– is 1s2)
- ALLOW H2
![6 Which element has atoms with the greatest number of singly occupied orbitals?
A C
B Cl
C Ca
D Ga
Your answer [1]](/img/JUN17_H0321/JUN17_H0321_06.webp)
Answer
A
Mark scheme
![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]](/img/JUN17_H4321/JUN17_H4321_15.webp)
Answer
B
Mark scheme
Earlier part of question 22 that this part uses
(i).webp)
![(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]](/img/JUN17_H0321/JUN17_H0321_22(c)(iv).webp)
Mark scheme
(iv)_MS.webp)
Notes from the mark scheme and report
- Mg electron from (3)s AND Al from (3)p
- 3p higher energy than 3s
- DO NOT ALLOW unpaired electron removed more easily
- IGNORE distance from nucleus
![(c) Barium nitride is formed when barium is heated with nitrogen.
(i) Complete the electron configuration of a nitride ion.
1s2 ................................................................................................................................. [1]](/img/JUN17_H0322/JUN17_H0322_01(c)(i).webp)
Mark scheme
(i)_MS.webp)
Notes from the mark scheme and report
- 2s2 2p6 (nitride is N3–)
- ALLOW upper case and subscripts
![6 How many orbitals are occupied in a silicon atom?
A 5
B 7
C 8
D 9
Your answer [1]](/img/JUN16_H0321/JUN16_H0321_06.webp)
Answer
C
Mark scheme
![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]](/img/JUN16_H0321/JUN16_H0321_23(a)(i).webp)
Mark scheme
(i)_MS.webp)
Notes from the mark scheme and report
- DO NOT ALLOW [Ar] shorthand
- ALLOW 3d after 4s or 4p
![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]](/img/JUN16_H0322/JUN16_H0322_01(a)(i).webp)
Mark scheme
(i)_MS.webp)
Notes from the mark scheme and report
- ALLOW upper case S and P, and subscripts
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