Group 2 Elements

Basics

Group 2 elements are called alkaline earth metals

They always have an electronic configuration that ends with S²

All group 2 carbonates are insoluble. None of the carbonates are soluble

Density

The density down the group increases. However, there are some exceptions

Boiling and Melting Points

The melting and boiling point down the group decreases in a general trend. This is due to the charge density of the metal cations. As the size of the cation increases, then the charge density also decreases. This reduces the electrostatic attraction forces between the sea of delocalised electrons and the metal cations.

Reactivity

The reacivity increases down the group

Solubility

Now there is a pattern of particular compounds down the group. We will especially look at hydroxides and sulfates. The reason is not required but will be dicussed in A2 chemistry

Atomic radius

Down the group, the atomic radius increases down the group. This is because, down the group, more electron are added to new electron shells. The shielding effect also increases as more inner core electrons. So the nuclear charge or attraction force between the valence electrons and nucleus decreases so the radius increases. This could applied to Ionisation energy and electronegativity also

Ionisation energies

As electrons are added to new principal quantum shells, the shielding effect due to inner core electrons increases. Also the radius increases. So this will reduce the effective nucleur charge between the valence electron and the nucleus. So the ionisation energy will decrease down the group

Electronegativity

The electronegativity also decreases down the group and this is due to the same reasons as Ionisation energy

Uses of Group 2 Elements

Group 2 elements has a range of uses and it is a good idea to remember the table below:

Compound	Uses
MgSO4	Used as epson salt as bath salts
CaOH2	To treat acidified soil or lakes
CaO & CaCO3	To treat acidified soil or lakes and also used to make cement and concrete
BaSO4	Used for X-ray imaging of large intestines ( Barium meal )
MgOH2	Used as antiacids for stomach // Milk of magnesia
MgO	Used for lining of furnaces and in strong ceramic production

Hydroxides

The solubility of hydroxides increases down the group. This means that barium and strontium hydroxides are soluble than magnesium hydroxide.

You need to know the solubility of each element

Element	Solubility
Mg(OH)2	Insoluble
Ca(OH)2	Slightly soluble
Sr(OH)2	Soluble
Ba(OH)2	Highly soluble

This can be also used to predict the solubility of the group 2 oxides. This is because when group 2 oxides dissolve in water, OH^- ions are released

O^2- + H²O → 2OH^-

So the solubility of oxides also has the same trend

Element	Solubility
MgO	Insoluble
CaO	Slightly soluble
SrO	Soluble
BaO	Highly soluble

The more soluble the hydroxide, the more OH^- ions are released. This increases the pH of the alkali.

Element	pH
Mg(OH)2	7
Ca(OH)2	11
Sr(OH)2	14
Ba(OH)2	14

Sulfates

The sulfates follows the opposite trend of the hydroxides. The solubilty decreases down the group

Element	Solubility
MgSO4	Soluble
CaSO4	very slightly soluble
SrSO4	insoluble
BaSO4	insoluble

Remember this table! For example:

Mg(NO₃)₂ + H₂SO₄

This will cause no reaction as they will form a mixture of ions. This is because magnesium sulfate is soluble

Ba(NO₃)₂ + H₂SO₄ → BaSO₄ + HNO₃

This will cause a white ppt formed which is barium sulfate

Thermal Stability of Carbonates & Nitrates

Down the group the thermal stability increases. This means it needs a high temperature to decompose. In other words, the ease of decomposition decreases down the group

We will see the products formed when heated, we will take an example for each:

Nitrates are broken down to oxides, nitrogen and oxygen gas

2Mg(NO₃)₂ → 4NO₂ + 2O₂ + 2MgO

For Carbonates, the products are carbon dioxide and oxides:

MgCO₃ → CO₂ + MgO