Alkaline Earth Metal 

Any element of the periodic table which is in group 2.
In order of proton number, Beryllium, Magnesium, Calcium, Strontium, Barium and Radium are all Alkaline Earth Metals.

They are characterized by all having 2 outer-shell electrons (two electrons in their valence shell), alas their placing in group 2 of the periodic table.

They are all silver coloured, soft metals which react readily to form ionic compounds.

The name 'Alkaline Earth Metals' is derived from the fact that the oxides formed by the elements in this group produce basic Alkaline solutions, and the melting points are such that the elements remain solid (Earths) in fires. Alkaline Earth refers to the oxides themselves.

x + 2H2O --> x(OH)2 + H2

2x + O2 --> 2xO
2xO + 2H2O --> 2x(OH)2

Where x is an Alkaline Earth Metal.
Both processes are relatively efficient unless you consider Hydrogen, which is produced in the first, to be a waste product. The second process only produces the hydroxide.

Magnesium is an Alkaline Earth Metal - it, and its oxide, react with water to form a basic alkaline solution.

Mg + 2H2O --> Mg(OH)2 + H2
Magnesium + Water --> Magnesium Hydroxide + Hydrogen

2Mg + O2 --> 2MgO
Magnesium + Oxygen --> Magnesium Oxide
2MgO + 2H2O --> 2Mg(OH)2
Magnesium Oxide + Water --> Magnesium Hydroxide

The electron configuration of Magnesium is 2,8,2 - two electrons in its outer/valence shell

Alkaline Earth Metal by Aconymous November 15, 2009