Periodic trends — KCSE Chemistry

KCSE Chemistry · 56 practice questions · 4 syllabus objectives

21 easy23 medium12 hard

What You'll Learn

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

Explain trends in atomic radius, ionisation energy, electronegativity and electron affinity across a period and down a group

Relate periodic trends to electronic configuration and nuclear charge

Predict the properties of an element from its position in the periodic table

Periodic trends

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easySHORT ANSWER4 marks

Name two properties of elements found in Group 1 of the periodic table and explain how their position influences these properties. (4 marks)

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Part (a) — 2 marks

Low ionization energy (1 mk)

High reactivity with water (1 mk)

Part (b) — 2 marks

Elements have one electron in their outer shell, making it easier to lose an electron (1 mk)

The atomic radius increases down the group, resulting in decreased attraction between the nucleus and the outer electron (1 mk)

easySHORT ANSWER4 marks

Define the term 'electronegativity' and explain how it varies within group 17 from fluorine to iodine. (4 marks)

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Part (a) — 1 mark

Electronegativity is the ability of an atom to attract electrons in a bond (1 mk)

Part (b) — 3 marks

Electronegativity decreases from fluorine to iodine (1 mk)

This is due to increasing atomic size, which means the nucleus is further from the bonding electrons (1 mk)

Increased electron shielding also contributes to the decrease in electronegativity (1 mk)

easySHORT ANSWER3 marks

Explain how the first ionization energy changes as you move from potassium to calcium in period 4. (3 marks)

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Part (a) — 3 marks

First ionization energy increases from potassium to calcium (1 mk)

This is due to an increase in nuclear charge as protons increase (1 mk)

The outermost electron is not significantly shielded, making it harder to remove (1 mk)

Identify the element in Period 3 with the highest electronegativity. Explain your answer. (3 marks)