Chemical Properties of Alkaline Earth Metals

Alkaline Earth Metals are also known as group 2 metals. Group 2 metals include beryllium, magnesium, calcium, strontium, barium, and radium. Excluding beryllium, all of the group 2 metals are called alkaline earth metals. They react with oxygen, water, and dilute acids. These metals are given this name because their oxides and hydroxides act alkaline in nature. The metal oxides are found in the Earth’s crust. Alkaline earth metals conduct electricity and are metallic. They also form metallic bonds. They can donate 2 electrons which then change their oxidation states to +2.  The electronic configuration for alkaline earth metals is ns2.

For example, electronic configuration for Na is = 1s2 2s2 2p6 3s2

Reactions with oxygen

• Metal oxides are formed when alkaline earth metals react with oxygen. 

• The general equation is = 2M(s) + O2(g) → 2MO(s)

Here M = Metal 

MO = Metal oxide

• Strontium and Barium react with oxygen to form SrO2 and BrO2, respectively.
  
  
• Alkaline earth metals react with water to form hydroxides.

General equation = Oxides + colourlessHydroxides 

Example = Calcium Oxide(Quick lime) + Water → Calcium hydroxide (also known as limewater)

• When alkaline earth metal oxides react with acids, they form colourless salt solutions and water.

Metal oxide + HCl → Salt + water

Metal Oxide + H2SO4 → Sulphate + water

• Group 2 hydroxides react with acid to form metal chlorides that are colourless and water.
  
  

Metal hydroxide + HCl → salt + water

Metal hydroxide + H2SO4 → sulphate + water  

Reaction with water 

• Group 2 metals form metal hydroxides by reacting with water. 

Beryllium is an exception. It does not react with water.

• Group 2 metals reactivity increases with water, going down the group.
• Metal hydroxides also become more soluble down the group.
• General equation for the reactions is = M(s) + 2H2O(l) → M(OH)2(s) + H2(g)

Reaction with acid  

• Alkaline earth metals react with HCl to form a colourless solution of a metal chloride, and hydrogen gas is released.
• General equation = M + 2HCl → MCl2  + H2  
• Reactions turn more vigorous down the group

• Alkaline earth metals react with dilute sulfuric acid to give metal sulphates.
• It is a colourless solution of metal sulphate reaction, and hydrogen gas is given off.
• General equation = M(s) + H2SO4(aq) → MSO4(aq) + H2(g)
• The solubility of sulphates decreases down the group

Reaction with Group 2 Carbonates 

• When group 2 carbonates are reacted with water, they prove to be insoluble. Only Beryllium Carbonate (BeCO3) dissolves and reacts in water.
  
  
• Reacting Carbonates with dilute HCl results in
• Soluble chloride salt
• Water 
• Carbon dioxide gas
•  Reacting carbonates with dilute H2SO4 results in 
• Sulphate 
• Water
• Carbon dioxide gas 

Alkaline earth metals basic trends 

• All group 2 metals form metal ions that have a charge of 2+. They lose 2 electrons from their outer electrons.
• The metal cations are smaller in size at the top, and size increases as we go down the group.
• The atomic radius of group 2 metals keeps on increasing going down. 
• The charge. The density of the group 2 metals decreases going down the group. 
• At the top of group 2, the charge is denser because electrons are packed in a smaller volume.
• Thermal stability increases down the group. 
• Cations become larger. So the charge density lowers down.
• The smaller group 2 ions form a higher polarising effect. 
• High heat is required to thermally decompose them.
• Going down the group, the solubility of hydroxides of alkaline earth metals increases.
• Going down the group, the solubility of carbonates of alkaline earth metals decreases.

Conclusion

Alkaline earth metals are also known as group 2 metals. They have an oxidation number of +2. Group 2 metals have a high melting and boiling point. They react more vigorously down the group when reacting with water. Group 2 metals have a smaller ionic radius at the top; then, the radius keeps on increasing as we go down. The sulphates of group 2 metals become less soluble down the group. When carbonates of group 2 metals are reacted with water, they are insoluble, except for beryllium. The carbonates that are formed by group 2 metals are usually insoluble in water. Reacting group 2 carbonates with water results in salt + water + carbon dioxide as products.