Magnesium and Its Properties

Magnesium Mg(Z=12) in Group 2 Alkaline Earth Metals

The structure of the element:
Giant lattice metallic structure of immobile positive metal ions surrounded by a 'sea' of freely moving mobile electrons (so-called delocalised electrons).

Physical properties:
A moderately hard silvery-white solid; mpt 649oC; bpt 1090oC; good conductor of heat/electricity.

Group, electron configuration (and oxidation states):
Gp2 Alkaline Earth Metal; e.c. 2,8,2 or 1s2 2s2 2p6 3s2; (+2 only) e.g. MgCl2, MgO.

Reaction of element with oxygen:
Burns brightly when heated in air to form a white powder of ionic magnesium oxide Mg2+O2- when heated strongly in air.
2Mg(s) + O2(g) ==> 2MgO(s)

Reaction of oxide with water:
It is slightly soluble in water, and is a basic oxide forming an alkaline solution of magnesium hydroxide
Mg2+(OH-)2, of about pH12.
MgO(s) + H2O(l) ==> Mg(OH)2(aq) Reaction of oxide with acids:
Behaves as a basic oxide dissolving to form the chloride, sulphate and nitrate salt in the relevant dilute acid.
MgO(s) + 2HCl(aq) ==> MgCl2(aq) + H2O(l)
MgO(s) + H2SO4(aq) ==> MgSO4(aq) + H2O(l)
MgO(s) + 2HNO3(aq) ==> Mg(NO3)2(aq) + H2O(l)
In all cases the ionic equation is: MgO(s) + 2H+(aq) ==> Mg2+(aq) + H2O(l)

Reaction of oxide with strong bases/alkalis:
No reaction.

Reaction of element with chlorine:
Forms colourless solid ionic magnesium chloride, Mg2+(Cl-)2, when heated in chlorine.
Mg(s) + Cl2(g) ==> MgCl2(s)

Reaction of chloride with water:
The salt dissolves in water forming a nearly neutral solution of about pH6.
MgCl2(s) + aq ==> Mg2+(aq) + 2Cl-(aq) or MgCl2(s) + 6H2O(l) ==> [Mg(H2O)6]2+(aq) + 2Cl-(aq)
The solution is slightly acidic(may assume to just dissolve) asthe following reaction occurs:
[Mg(H2O)6]2+(aq) + H2O(l) [Mg(H2O)5OH]+(aq) + H3O+(aq) Reaction of element with water:
Very slow reaction with cold water to form hydrogen (bubbles form slowly on the surface) and alkaline magnesium hydroxide.