Group II metals
The electronic configuration of the group 3 elements is shown below:
|Be – Beryllium||2,2|
|Mg – Magnesium||2,8,2|
|Ca – Calcium||2,8,8,2|
Similarly to the group 1 elements, the group II elements react by losing electrons. This happens in order to achieve the electronic configuration of the closest Nobel gas. As a result, positive ions are formed with a charge of 2+.
The ability to lose these electrons increases down the group resulting in an increase in reactivity. This increase in reactivity is caused by an increase in the size of the elements as you go down the group, followed by a loss in attraction between the nucleus and the surrounding outer electrons (electrons are further away and thus electrostatic forces of attraction between a positive and negative charge is less). As a result, the electrons on the outer shell of the larger elements are more easily lost during a reaction. With this in mind, the order of reactivity is as follows:
Properties of the group II metals
|Be||Shiny grey metal||1287||2900||1.86|
|Mg||Shiny white metal||650||1105||1.77|
|Ca||Shiny white metal||850||1440||1.55|
Trends in Group II
Density decreases down the group as the atoms increase in size. As you go down group 2 there is an increase in both mass and volume as we would expect from the increase in atomic mass and atomic number. However the rate at which the volume increases down the group is more significant than the rate of increase in mass because the electrons are being placed in shells further and further away from the nucleus thus occupying more space (increase in volume). Also, since electrons are negatively charged there is a slight repulsion between electron shells which also increases volume. Since Density= Mass/ Volume, and the rate at which the volume increases is greater than the rate at which the mass increases. Then there is a decrease in Density as we move down the group.
Melting and Boiling Point
Boiling and Melting points decrease with an increase in atomic size. As atomic size increases the forces of attraction between atoms decrease. As a result there is a decrease in melting and boiling points because less energy is required to break these inter-atomic forces of attraction (forces of attraction between atoms).
Reaction with Oxygen
Metals within the group II react rapidly with air to form a film or layer of oxide. The rate of reaction increases with increased atomic size as is expected.
Beryllium + Oxygen → Beryllium Oxide
Magnesium + Oxygen → Magnesium Oxide
Calcium + Oxygen → Calcium Oxide
Reaction with Water
Reactivity with water also increases as you move down the group.
Beryllium does not react with water – neither hot nor cold.
Magnesium reacts very slowly with water to form magnesium hydroxide
Magnesium + Water → Magnesium Hydroxide
Calcium reacts moderately with water to form calcium hydroxide
Calcium + Water → Calcium Hydroxide
Strontium and Barium reacts explosively with water.
Reaction with Dilute acid
Members of this group react with dilute acid to form a salt and hydrogen gas.
Since we know that reactivity increases down the group as the atoms get larger, and then we should know too that the reaction becomes more vigorous as we move from beryllium to barium.
Beryllium + Sulphuric acid → Beryllium Sulphate (salt) + Hydrogen gas
Beryllium + Hydrochloric acid → Beryllium Chloride (salt) + Hydrogen gas
The reaction is the same for all group 2 metals, for example:
Magnesium + Sulphuric acid → Magnesium Sulphate + Hydrogen gas
Calcium + Sulphuric acid → Calcium Sulphate + Hydrogen gas