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diagonal relationship between mg and li

diagonal relationship between mg and li


1 Answers

sumit kumar
askIITians Faculty 13 Points
7 years ago
  1. The reason for resemblance of properties of lithium with magnesium is that these two elements have almost same polarizing power.
  2. The following points illustrate the anomalous properties of lithium and its diagonal relationship with magnesium:
  3. The melting point and boiling point of lithium are comparatively high.
  4. Lithium is much harder than the other alkali metals. Magnesium is also hard metal.
  5. Lithium reacts with oxygen least readily to form normal oxide whereas other alkali metals form peroxides and superoxides.
  6. LiOH like Mg (OH)2 is weak base. Hydroxides of other alkali metals are strong bases.
  7. Due to their appreciable covalent nature, the halides and alkyls of lithum and magnesium are soluble in organic solvents.
  8. Unlike elements of group 1 but like magnesium. Lithium forms nitride with nitrogen.6Li + N2 → 2Li3N
  9. LiCl is deliquescent and crystallizes as a hydrate, LiCI2H2O. Other alkali metals do not form hydrates. also forms hydrate, MgCI2.8H2O .
  10. Unlike other alkali metals lithium reacts directly with carbon to form an ionic carbide. Magnesium also forms a similar carbide.
  11. The carbonates, hydroxides and nitrates of lithium as well as magnesium decompose on heating.
    Li2CO3→ Li2O + CO2
    MgCO3→ MgO + CO2
    2LiOH → Li2O + H2O
    Mg (OH)2 → MgO + H2O
    4LiNO3 → 2Li2O + 4NO2 + O2
    2Mg ( NO3)2 → 2Mg + 4NO2 +O2
    The corresponding salts of other alkali metals are stable towards heat.
  12. Lithium nitrate, on heating, decomposes to give lithium oxide, Li2O whereas other alkali metals nitrate decomposes to give the corresponding nitrite.
    4LiNO3 → 2Li2O + 4NO2 + O2
    2NaNO3 → 2NaNO2 + O2
    2KNO3 → 2KNO2 + O2
  13. Li2CO3, LiOH, LiF and Li3PO4 are the only alkali metal salts which are insoluble in water. The corresponding magnesium compounds are also insoluble in water.
  14. Hydrogen carbonates of both lithium and magnesium can not be isolated in solid state. Hydrogen carbonates of other alkali metals can be isolated in solid state.
Thanks & Regards
Sumit Kumar
askIITians Faculty

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