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.

Similarities with Magnesium

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