Group 2: ionisation energy and properties

In a nutshell

As you go down Group $2$ in the periodic table, the atomic radius and reactivity increase, whilst the ionisation energy and melting points decrease for Group $2$ metals.

Chemistry; Inorganic chemistry and the periodic table; KS5 Year 12; Group 2: ionisation energy and properties

Electron configuration

Element	Atom	Ion
$Be$	$1s^22s^2$	$1s^2$
$Mg$	$1s^22s^22p^63s^2$	$1s^22s^22p^6$
$Ca$	$1s^22s^22p^63s^23p^64s^2$	$1s^22s^22p^63s^23p^6$

As Group $2$ elements react, they tend to lose their two outermost electrons and form $2+$ ions.

Atomic radius

For Group $2$ elements the atomic radius decreases as you go down the group. This is because electron shells are added as you go down the group which causes an increase in radius.

First ionisation energy

For Group $2$ elements as you go down the group an extra electron shell is added. The inner shells shield the outer shell from the nucleus. This weakens the attraction of the outer electrons to the nucleus making them easier to remove. Thus, decreasing the first ionisation energy as you go down the group.

Reactivity

As you do down Group $2$ , reactivity increases. This is due to the first ionisation energy decreasing as you go down the group. Since less energy is required to remove the outermost electrons as you go down the group, this means it's easier for the metals to react. Therefore reactivity of the Group $2$ metals increases down the group.

Melting points

Group $2$ metals have metallic structures with positive ions surrounded by delocalised electrons. Going down the group the metal ions get bigger, but the charge remains the same, $2+$ . This means that charge density decreases resulting in a weaker attraction between atoms. This means less energy is required to separate the atoms.

Group 2 and water

When Group $2$ elements react with water they are oxidised and their oxidation number changes from $0$ to $+2$ . This forms $M^{2+}$ ions.

Example

$Ca\ +\ 2H_2O\ \rightarrow\ Ca(OH)_2\ +\ H_2\\0 \, \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,+2 \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \,\,\,\,\,\,\,\,\,\\Ca \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,Ca^{2+}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,$