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Trend in atomic radius of Group 2 elements

What is here?

Atomic radius increases going down Group 2. You can:

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Table of physical data

Element

Proton number

Symbol

Atomic radius (nm)

beryllium

4

Be

0.125

magnesium

12

Mg

0.160

calcium

20

Ca

0.174

strontium

38

Sr

0.191

barium

56

Ba

0.198

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Graph of physical data

Graph of atomic radii of Group 2 elements

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Explanation of this trend

Going down Group 2:

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

As the number of protons in the nucleus increases going down Group 2, you might expect the atomic radius to decrease because the nuclear charge increases. This does not happen,  because although the electrons in the inner energy levels become closer to the nucleus, the factors described above have a greater influence on the atomic radius overall.

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