Group 2 - The Alkaline Earth Metals

All members of Group 2 have two electrons in there outer s-orbital. The s-orbital become further away from the nucleus as we go down the group.

The atoms get bigger as you go down the group, as each member has an extra level of electrons than the previos member.

All the members have high melting points as they all have giant metallic structures. As the atom size increases, the delocalized sea of electrons gets further away from the nucleus meaning the force of attraction is weaker and less energy is required to break the metallic bond. As a result the melting points decrease slightly down the group.

Magnesium is an exception as it has a lattice arrangement different to the other elements which makes them easier to separate.

In all there reactions Group 2 elements lose two electrons to have a positive charge.

M--->M2+ + 2e-

Both the first an second ionisation energy decrease as we go down the group. As the atom size increases the outer shell become further from the nucleus, reducing the force of attraction, meaning less energy is required to remove an electron. the nucleus is shielded by more inner shells.

All the Group 2 elements are oxidised in all there reaction going from oxidation stat 0 to oxidation state +2.

The metals get more reactive with water as we go down the group. These are Redox reactions. The basic reaction is

M(s) + 2H2O(l) --> M(OH)2(aq) + H2(g)

M is any of the group 2 elements.

The hydroxides get more soluble as you go down the group. They are all white solids.

Magnesium is alomost insoluble, being sold in a suspension in water rather than as a solution.

Calcium Hydroxide is sparyingly soluble.

Strontium Hydroxide is more soluble.

Barium Hydroxide dissolves and forms a strong alkaline solution as seen below

Ba(OH)2(s) + aq --> Ba2+(aq) + 2OH-(aq)

The sulfates become less soluble down the group. Barium Sulfate is used as a test for Sulfates ions in solution.

The solution is acidified with nitric or hydrochloric acid.

Barium Chloride solution is added to the solution under test.

If Sulfate is present a white precipitate of Barium Sulfate is formed.

Ba2+(aq) + SO4(2-) (aq) --> BaSO4(s)

The addition of acid removes the carbonate ions as Barium Carbonate is also a white solid like Barium Sulfate.

Barium Sulfate can be taken by mouth as a 'barium meal' to outline the gut in medical X-rays as it is virtually insoluble.

Magnesium Hydroxide is 'milk of magnesia' used in indigestion remedies to neutralise excess stomach acid.

Calcium Hydroxide is know as 'slaked lime' to neutralise acidified soil. Oats corn and barley prefer neutral soil while grass prefers pH6