Group 2- Alkaline Earth Metals

trends, reactios, solubility

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  • Created by: melissa
  • Created on: 08-04-12 14:25

Properties

Atomic radius/ ionic radius...INCREASES...due to an increasing number of electron shells. Charge to size ratio decreases so less attraction

First ionisation energy...DECREASES...because outer electrons are further from the nucleus with increased distance and shielding. Metals are more reactive down the group.

Melting point...DECREASES...All have high melting points. Positive ions are surrounded by a sea of delocalised electrons. Larger metals have weaker metallic bonds. Mg is different as it has a different crystal structure.

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Reactions with water

Be doesnt react.

Mg slow with water but readily with steam:

cold: Mg(s) + 2H2O(l) Mg(OH)2(s) + H2(g)

steam: Mg(s) + H2O(g) MgO(s) + H2(g)

Ca, Sr and Ba all react readily with water.

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Solubility

Sulphates of group 2 become more insoluble down the group.

MgSO4 is soluble BaSO4  isnt soluble

Ba2+ + SO42- → BaSO4

BaSO4 is used in x-rays as it blocks them and although it is toxic, Ba canno be dissolved in water or bodily fluids.

 

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solubility

The hydroxides of group 2 become more soluble own the group.   Mg(OH)2(s)+ 2H → Mg2+ +2H2O Mg(OH)2 acts as a laxative/ antacid (relieves indigestion). Almost insoluble Ba(OH)2(s)+ aq →Ba2++2OH- Strong alkaline solution when dissolved in water

Ca(OH)2 reduces soil acidity

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