The group 2 elements are called the alkaline earth metals. The physical properties and chemical reactivity depend upon the electronic structure of the elements.

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Alkesh Chohan                Chemistry

Group 2  trends

  • The group 2 elements are called the alkaline earth metals. The physical properties and chemical reactivity depend upon the electronic structure of the elements.

Atomic radius – the distance between nucleus and the outer shell (measured in units nm)

Trend – atomic radius increases down the group

Explanation

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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First ionisation energy – the amount of energy required (Kjmol-1) to remove an electron from a gaseous atom

Trend – as you can see, the first ionisation energy decreases going down the group.

Explanation

There are more filled energy levels between the nucleus and the outer electron; these shield the outer electron from the attraction of the nucleus.

The radius of the atom increases, so the distance between the nucleus and the outer electron increases therefore the force of attraction between the nucleus and outer electron is reduced so less energy is needed to remove the outer electron.

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