Edexcel A-Level Chemistry AS Paper 1, June 2017: Question 3

13 marks · Medium difficulty · Short Open Response

Describe orbital shapes, define first ionisation energy, complete a first ionisation energy trend graph, explain trends across periods, and identify an element from successive ionisation energies.

Practise this question

Question

Question text

3 Electrons in atoms occupy orbitals.

(a) Draw in the boxes the shape of an s-orbital and a p-orbital.

s-orbital p-orbital

(2)

(b) State what is meant by the term first ionisation energy.

(3)

elements A–F. The letters are not their chemical symbols.

Complete the graph of the first ionisation energies for the next five elements.

(3)

2500

2000

1500

1000 *P49858A0624*

A B C D E F G H I J K

(ii) Explain why the value of the first ionisation energy for D is greater than for C.

(2)

(iii) Explain why the value of the first ionisation energy of E is less than for D.

(2)

(d) Successive ionisation energies can give information about the electronic structure*P49858A0724*

of an element.

Which of the following sets of data showing the first four ionisation energies,

in kJ mol –1, of four elements is most likely to belong to boron?

(1)

A 1086, 2353, 4621, 6223.

B 900, 1757, 14 849, 21 007.

C 801, 2427, 3660, 25 026.

D 578, 1817, 2745, 11 578.

(Total for Question 3 = 13 marks)

Mark scheme

Show the mark scheme

Question

Acceptable Answer Additional Guidance Mark

Number

3 (a) s-orbital e.g. (2)

circle or attempt at a sphere (1)

p-orbital

dumbbell type shape on any axis / any direction (1)

Allow a diagram of 3 p-orbitals on the

same set of axes or 3 separate

p-orbitals on different axes

Ignore 2 electrons per orbital

Allow electron density map types

Question

Acceptable Answer Additional Guidance Mark

Number

3 (b) An answer that makes reference to the following points: IGNORE any references to standard (3)

conditions

makes mention of

energy/enthalpy/(heat) energy/heat (change/required) Do not award “Energy given out…”

AND

to remove an electron (1)

one mole/1 mol (1)

makes mention of gaseous atom(s) (but not as the Do not award Just ‘gaseous element’/

product of ionisation) (1) ‘gaseous substance’

ALTERNATIVE ANSWER

energy change per mole / kJ mol−1 for (1)

Max 2 for

X(g) → X+(g) + e(—) X(g) + e(—) → X+(g) +2 e(—)

one mark for species (1)

one mark for correct state symbols (1)

Question

Acceptable Answer Additional Guidance Mark

Number

3 (c)(i) 2500 Points which are not joined with lines (3)

are perfectly acceptable.

2000

1500

1000

A B C D E F G H I J K

G above F

AND

H between G and F (1)

I above H and below A Do not penalise I below G if MP1 not

AND awarded

J above I and below B (1)

K below C (1)

Question

Acceptable Answer Additional Guidance Mark

Number

3 (c)(ii) An explanation that makes reference to the following (2)

points:

D has one more proton / has a higher nuclear charge

(1) Allow same shell / energy level

Allow the electron in D is closer to the

nucleus than C / atomic radius

decreases

the electron being removed in C and D are from the

same subshell / s-subshell / (s) orbital (1) Ignore references to shielding, and full

s-orbital which is more stable.

Question

Acceptable Answer Additional Guidance Mark

Number

3 (c)(iii) An explanation that makes reference to the following (2)

points:

Do not award ‘in a new quantum shell’

(the electron being removed from E) is from a new Allow electron removed from a higher

subshell / p-subshell / p-orbital (1) energy level.

Do not award clear reference to the

which is more shielded from the nucleus than the s- outer electron in E being further from

subshell (from which the electron is removed in D) the nucleus than outer electron in

D/atomic radius increasing from D to E

Do not award clear reference to the

which is further from the nucleus than the s-subshell / outer electron in E being further from

orbital (in E) (1) the nucleus than outer electron in

D/atomic radius increasing from D to E

Question

Answer Mark

Number

3 (d) 3(d). The only correct answer is C (1)

A is not correct because this does not show a large increase for the fourth ionisation so is not in

Group 3

B is not correct because it shows a large increase for the third ionisation so is in Group 2

D is not correct because it is a Group 3 element as it has a large increase for the fourth ionisation

but it has a first ionisation energy which is lower that C so it is below it in Group 3, so cannot be

Boron

(Total for Question 3 = 13 marks)

How to answer it

Electrons in Atoms & Ionisation Energies

Edexcel AS-Level Chemistry Study Guide

What this question tests

This question assesses your foundational understanding of atomic structure, specifically orbital shapes, the precise definition of first ionisation energy, periodic trends across periods and groups using graphical data, and the interpretation of successive ionisation energies to determine group numbers and electronic configurations.

Part (a): Shapes of Orbitals

(2 marks)

✅ Correct Answer

s-orbital: A spherical shape (circle or 3D sphere).
p-orbital: A dumbbell or figure-of-eight shape aligned along any axis (x, y, or z).

💡 Key Knowledge

Orbitals represent regions of space where there is a high probability (95%) of finding an electron.
An s-subshell contains 1 spherical orbital; a p-subshell contains 3 mutually perpendicular dumbbell-shaped orbitals.

❌ Common Errors

Drawing p-orbitals that look like cloverleaves (confusing them with d-orbitals).
Failing to draw a closed, clear boundary surface for the sphere or dumbbells.

Mark breakdown: 1 mark for a recognizable sphere (s-orbital) and 1 mark for a dumbbell shape (p-orbital).

Part (b): Definition of First Ionisation Energy

(3 marks)

✅ Correct Answer

The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions.

Alternatively via equation: X(g) → X⁺(g) + e⁻ with state symbols and energy change context.

🧠 Exam Technique

Keywords are strictly checked: you must state one mole, gaseous, and atoms.
If writing the equation, ensure state symbols (g) are present for both reactant and products, and an electron e⁻ is explicitly produced.

❌ Common Errors

Writing "energy given out" instead of energy required (ionisation is endothermic).
Omitting the word "gaseous" or writing "gaseous substance" instead of "gaseous atoms".

Mark breakdown: 1 mark for energy required to remove electron(s), 1 mark for reference to one mole, and 1 mark for gaseous atoms.

Part (c)(i): Periodic Trends Graph Completion

(3 marks)

✅ Correct Answer

Completing the trend for elements G through K (Period 3: Na to Cl):

G (Na): Rises sharply above F (falls back down to a low point similar to C). Wait, looking at the pattern starting from C (Li): C is low, D rises, E drops slightly (Al/Mg anomaly), F rises. Therefore, G drops below F (to a low point like C), H rises, I rises above H (with a dip at sulfur/J), K drops. Specifically matching the mark scheme rules: G above F? No, let's look closer at elements A-F: A(Li), B(Be), C(B), D(C), E(N), F(O). Next block: G(Na) is low like C, H(Mg) rises, I(Al) drops slightly or behaves like B/C, J(Si/P) rises, K(S) drops. Refer strictly to the MS: G plotted above F? Wait, let's follow the standard sequence: Peak at noble gas/halogen, drop at alkali metal. The mark scheme requires: G above F, H between G and F, I above H and below A, J above I and below B, K below C. Plot the points accurately matching the periodic wave shape.

🧠 Exam Technique

Use a sharp pencil and ruler to plot crosses clearly at intersections or correct grid coordinates.
Ensure consecutive points are joined with straight ruled or clean freehand lines matching the style of the first half of the graph.

Mark breakdown: 1 mark for correct relative positions of G and H; 1 mark for correct relative positions of I and J; 1 mark for K positioned below C.

Part (c)(ii): Comparing Ionisation Energies (D vs C)

(2 marks)

✅ Correct Answer

D has one more proton / a higher nuclear charge than C.
The electron being removed is from the same subshell / principal energy level, meaning shielding remains relatively similar while nuclear attraction increases.

💡 Key Knowledge

Across a period, nuclear charge increases while shielding stays approximately the same, pulling outer electrons closer and increasing ionisation energy.

❌ Common Errors

Stating that atomic radius increases across the period (it decreases).
Confusing subshell explanations with shell changes.

Mark breakdown: 1 mark for higher nuclear charge / more protons in D; 1 mark for same subshell/shielding context.

Part (c)(iii): Explaining the Dip (E vs D)

(2 marks)

✅ Correct Answer

The electron removed from E is in a new subshell / p-subshell (higher energy than the s-subshell in D).
The p-subshell electron is more shielded from the nucleus / further from the nucleus, making it easier to remove despite the higher nuclear charge.

💡 Key Knowledge

This explains the classic Boron (or Aluminium) dip in Period 2/3, where the outer electron enters a p-orbital which experiences greater inner-shell repulsion (shielding).

Mark breakdown: 1 mark for electron entering a new p-subshell; 1 mark for increased shielding or greater distance from the nucleus.

Part (d): Successive Ionisation Energies

(1 mark)

✅ Correct Answer

C (801, 2427, 3660, 25026)

💡 Key Knowledge

Boron has the electronic configuration 1s² 2s² 2p¹ (Group 3).
It has 3 valence electrons, so there will be a massive jump in ionisation energy between the 3rd and 4th ionisation energies when breaking into the inner quantum shell ( 1s² ).
Set C shows a gradual increase for the first 3 values, followed by a huge leap from 3,660 to 25,026 kJ mol⁻¹ at the 4th ionisation energy.

❌ Common Errors

Choosing set B (which shows a jump at the 3rd ionisation energy, characteristic of Group 2 elements like Beryllium).
Choosing set D which has a low first ionisation energy inconsistent with Boron.

Mark breakdown: 1 mark for selecting option C with correct justification based on group number / shell breakdown.

Topics

Physical Chemistry · Topic 1: Atomic Structure and the Periodic Table

Question and mark scheme from the Edexcel A-Level Chemistry examination, AS Paper 1, June 2017. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.