Atomic radii of group 2 elements

Table of Contents Show

Learning outcomes
Atomic radius
Description of trend
Explanation of this trend
Does atomic radius increase in group 2?
How does atomic radius vary down group 2?
What element in group 2 has the largest atomic radius?
Which element in group 2 has smallest atomic radius?

Learning outcomes

After studying this page, you should be able to:

describe and explain the trend in atomic radius down group 2

Atomic radius

The table shows atomic radius values for the common elements in group 2 (the alkaline earth metals).

Element	Symbol	Atomic number	Atomic radius /nm
beryllium	Be	4	0.125
magnesium	Mg	12	0.160
calcium	Ca	20	0.174
strontium	Sr	38	0.191
barium	Ba	56	0.198

Atomic radius is the distance from the centre of the nucleus to the edge of the surrounding electron cloud. It is measured or calculated in different ways, so values vary from source to source.

Description of trend

The graph shows how atomic radius varies down group 2:

as the atomic number increases, the atomic radius increases.

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Explanation of this trend

Going down group 2:

there are more filled shells between the nucleus and the outer electrons …
the outer electrons are more shielded from the attraction of the nucleus …
so the electrons in the higher energy levels are further from the nucleus …
the atomic radius increases.

You might expect the atomic radius to decrease because the nuclear charge increases going down the group. However, this does not happen: although the electrons in the inner shells become closer to the nucleus, the factors described in the Explanation have a greater influence overall.

Does atomic radius increase in group 2?

Progressing down group 2, the atomic radius increases due to the extra shell of electrons for each element.

How does atomic radius vary down group 2?

The graph shows how atomic radius varies down group 2: as the atomic number increases, the atomic radius increases.

What element in group 2 has the largest atomic radius?

Ca and Mg belong to the Group II. The atomic radius decreases in moving from left to right along a period. This is due to an increase in nuclear charge which tends to pull the electrons closer to the nucleus and reduces the size of the atom. Hence K has largest atomic radii.

Which element in group 2 has smallest atomic radius?

As we move from left to right, atomic size decreases because of increase in nuclear charge but no change in the shells. Hence, Last element will be the smallest element in the period. Hence, fluorine has small radius in the second period.