Electronic configuration — KCSE Chemistry

KCSE Chemistry · 54 practice questions · 4 syllabus objectives

23 easy22 medium9 hard

What You'll Learn

Key learning outcomes for this topic, aligned to the KNEC KCSE syllabus.

Write the electronic configuration of elements using shells and sub-shells (s, p, d notation up to Z=20)

Relate the electronic configuration of an element to its position in the periodic table

Use electronic configuration to explain the chemical properties and valency of elements

Electronic configuration

Sample Questions

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1
easySHORT ANSWER4 marks

Identify the electronic configuration of Oxygen (Z = 8) and discuss how this configuration determines its group placement in the periodic table. (4 marks)

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Part (a) — 1 mark
Electronic configuration: 1s² 2s² 2p⁴ (1 mk)
Part (b) — 3 marks
Oxygen is in Group 16, as it has six electrons in its outer shell (1 mk)
The configuration indicates it requires two more electrons to achieve a full outer shell (1 mk)
This gives it properties consistent with nonmetals, such as forming covalent bonds (1 mk)
2
easySHORT ANSWER3 marks

Identify the electronic configuration of the following element and explain how it relates to its position in the periodic table: Lithium (Z = 3). (3 marks)

View Marking Scheme
Part (a) — 1 mark
Electronic configuration: 1s² 2s¹ (1 mk)
Part (b) — 2 marks
Lithium is in Group 1, indicating it has one electron in its outer shell (1 mk)
The configuration shows it is a metal, with properties of reactivity and forming cations (1 mk)
3
easySHORT ANSWER3 marks

List the electronic configurations of the following elements: (a) Lithium (Z = 3) (b) Beryllium (Z = 4) (c) Oxygen (Z = 8). (3 marks)

View Marking Scheme
Part (a) — 1 mark
Lithium (Z=3): Shell: 2,1 | Sub-shell: 1s² 2s¹ (1 mk)
Part (b) — 1 mark
Beryllium (Z=4): Shell: 2,2 | Sub-shell: 1s² 2s² (1 mk)
Part (c) — 1 mark
Oxygen (Z=8): Shell: 2,6 | Sub-shell: 1s² 2s² 2p⁴ (1 mk)
4

Write the electronic configuration of the following elements using shell and sub-shell notation: (a) Nitrogen (Z = 7) (b) Magnesium (Z = 12) (c) Fluorine (Z = 9) (d) Neon (Z = 10). (4 marks)

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