Question detail

Which statement correctly explains the trend in atomic radius and first ionisation energy for Group 2 elements?

Try the question, check the answer, then read the explanation to understand the curriculum point.

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At a glance

MCQ

Type

practice

Style

Topic

Group 2, the alkaline earth metals

Question

A. Both atomic radius and first ionisation energy increase down the group
B. Atomic radius increases while first ionisation energy decreases down the group
C. Both atomic radius and first ionisation energy decrease down the group
D. Atomic radius decreases while first ionisation energy increases down the group

Answer

Atomic radius increases while first ionisation energy decreases down the group

Explanation

As you move down Group 2, the atomic radius increases due to additional electron shells, while the first ionisation energy decreases due to increased distance from the nucleus and greater shielding effect.

Common mistake

Atomic radius trend misinterpreted

Students often think that the atomic radius of Group 2 elements increases because the number of electrons increases, but they ignore the effect of the increasing nuclear charge and the shielding by inner electrons.

Explain that as you move down Group 2 the principal quantum number increases, adding a new shell which outweighs the increased nuclear charge, so the outer electrons are further from the nucleus and the atomic radius increases. Use the rule that the effective nuclear charge felt by the outermost electrons decreases slightly because of shielding, leading to a larger radius.

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