Anomalous Properties of Lithium

• It is more harder and lighter than other alkali metals
• If is not affected by air easily and does not lose its lustre even on melting.
•  It reacts slowly with water to liberate hydrogen.
• Lithium is the only alkali metal which directly reacts with nitrogen to form Li₃N
•  Lithium hydroxide decomposes when heated to form Li₂O.  Hydroxides of other alkali metals do not decompose.
  2 LiOH → Li₂O + H₂O
• LiHCO₃ is known in solution but not in solid state.
• LiHCO₃ is less stable, as it decomposes on heating.
  LiHCO₃ → Li₂O + CO₂ + H₂O
• LiNO₃ on heating gives a mixture of NO₂ and O₂ while nitrates of rest of alkali metals yield only oxygen.
  4 LiNO₃ → 2Li₂O + 4NO₂ + O₂
  2NaNO₃ → 2NaNO₂ + O₂
• Li₂SO₄ is the only alkali metal sulphate which does not form double salts.
• Lithium reacts with bromine very slowly, other alkali metals react violently.
• LiF, Li₃PO₄, Li₂C₂O₄, Li₂CO₃ are sparingly soluble in water.
• LiCl is highly deliquescent and soluble in alcohol and pyridine.

Lithium shows anomalous behavior due to the following reasons:

1. Extremely small size of lithium atom and its ion.
2. Greater polarizing power of lithium ion (Li⁺) due to its small size which results in covalent character in its compounds.
3. Least electropositive character and highest ionization enthalpy as compared to other alkali metals.

Diagonal Relationship:

Similarities with Magnesium:

     Lithium shows resemblance with magnesium, an element of group IIA. This resemblance is termed as diagonal relationship.

Reasons for the diagonal relationship:

• Electro negatives of Li and Mg are quite comparable.
• Atomic radii and ionic radii of Li and Mg are not much different.
• Atomic volumes of Li and Mg are quite similar.
• Both have high polarizing power.

Lithium and Magnesium resembles:

1. Both Li and Mg are harder and have higher melting points than the other metals in their respective groups.
2. Li like Mg decomposes water slowly to liberate hydrogen.
   2Li + 2H₂O → 2LiOH + H₂
   Mg + 2H₂O → Mg (OH)₂ + H₂
3. Both the elements combine with nitrogen on heating
   6Li + N₂ → 2Li₃N
   3Mg + N₂ → Mg₃N₂
4. Both Li and Mg combine with carbon on heating.
   2Li + 2C → Li₂C₂
   Mg + 2C → MgC₂
5. Lithium forms monoxide when heated in oxygen. Mg also forms monoxide.
   4Li + O₂ → 2Li₂O
   2Mg + O₂ → 2MgO
   Both the oxides are less soluble in water