Question
Sat September 10, 2011 By: Mitali Joshi

What is the difference between alkali metals and alkali earth metals

Expert Reply
Sat September 10, 2011
Alkali and alkaline earth metals belong to S-block elements. As the outer electronic configuration of these two groups is similar they show similarity in most of their properties. However, there are certain differences in the properties of the elements belonging to these two groups. Let us discuss the differences in the nature, properties and reactivity of alkali and alkaline earth metals.
  • Nature of the elements: alkali metals are soft in nature when compared to alkaline earth metals.

  • Oxidation state: alkali earth metals exhibit an oxidation state of +1. Alkaline earth metals which have two electrons in the outermost s-orbital exhibit an oxidation state of +2.

  • Reactivity with nitrogen: alkali metals do not react with nitrogen directly. Alkaline earth metals combine with nitrogen directly and form nitrides.

  • Reaction with ammonia: alkali metals react with ammonia forming amides. Alkaline earth metals react with ammonia at low temperature forming hexamines M (NH36

  • Stability of the carbonates: carbonates formed by alkali metals are very stable compared to those formed by alkaline earth metals. Carbonates of alkaline earth metals decompose easily upon heating.

  • Decomposition of nitrates: nitrates formed by alkali metals decompose evolving oxygen. NO2 is liberated by decomposition of nitrates formed by alkaline earth metals. 

    2KNO3 ? 2KNO2 + O2 

    2Ba (NO3)2 ? 2BaO + 4NO2 + O2

  • Solubility of sulphates: Sulphates formed by alkali metals are highly soluble and form alums very easily. Sulphates of alkaline earth metals are sparingly soluble and do not form alums.

  • Solubility of bicarbonates: bicarbonates of alkali metals are less soluble than their corresponding carbonates. But, the bicarbonates of alkaline earth metals are more soluble than their corresponding carbonates.

  • Solubility of fluorides, carbonates, phosphates and oxalates: fluorides, carbonates, phosphates and oxalates of alkali metals are soluble. While those of alkaline earth metals are insoluble.
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