Anomalous Behaviour of Berllium

  • It is the hardest of all alkaline earth metals.
  • The melting and boiling points of the beryllium are the highest.
  • It is not effected by atmosphere.
  • It does not decompose water.
  • It has the tendency to form covalent compounds.
  • It does not react directly with hydrogen.
  • It dissolves in alkaline with evolution of hydrogen.
  • It does not liberate hydrogen from acids readily.
  • Its oxide is atmosphere in nature.
  • Its hydroxide is atmospheric in nature.
  • Its carbide (Be2C) on hydrolysis evolves methane:
    Be2C + 4H2O → 2 Be (OH) 2 + CH4
    The carbides of other alkaline earth metals (MC2) evolve acetylene on hydrolysis.
  • Its carbonate (BeCO3) is not stable towards heat.
  • Its nitride (Be3N2). Is volatile. Be3Nis covalent rest of the nitrides are ionic.

Beryllium has a unique chemical behavior due to it’s:

  1. small size
  2. high charge to size ratio
  3. high electronegativity

Diagonal relationship between Be and Al:

Diagonal relationship between Be and Al

The following are the causes of diagonal relationship:

  • The polarizing power of Be2+ and Al+3 ions is high consequently the compounds develop covalent nature.
  • The standard oxidation potential values of both the elements are very close to each other.
  • The electronegativity values of both elements are the same

Similarities in properties are listed below:

  • In nature, both the elements occur together in the mineral, beryl, 3BeO.Al2O3.6SiO2
  • Both are effected by atmosphere.
  • They do not decompose water.
  • Both become passive when treated with concentrated HNO3
  • Both dissolve in caustic alkalis liberating hydrogen.
  • Both BeO and Al2O3 are atmospheric in nature.
    BeO + H2SO4 → BeSO4 + H2O
    BeO + 2NaOH → Na2BeO2 + H2O
    Al2O3 + 6HCl → 2AlCl3 + 3H2O
    Al2O3 + 2NaOH → 2NaAlO2 + H2O
  • The hydroxides are also amphoteric in nature.
    Be (OH) 2 + 2HCl → BeCl2 + 2H2O
    Be (OH) 2 + 2NaOH → Na2BeO2 + 2H2O
    Al (OH) 3 + 3HCl → AlCl3 + 3H2O
    Al (OH) 3 + NaOH → NaAlO2 + 2H2O
    The hydroxides are insoluble in water and decompose on heating into corresponding oxides.
  • Beryllium carbide (Be2C) and Aluminium carbide (Al4C3) both evolve methane on treatment with water
    Be2C + 2H2O → 2BeO + CH4
    Al4C3 + 6H2O → 2Al2O3 + 3CH4
  • Beryllium and aluminium both form polymeric covalent hydrides.
  • Both combine with nitrogen when strongly heated in its atmosphere.
    3Be + N2 → Be3N22Al + N2 → 2AlNNitrides on action with water evolve ammonia
    Be3N2 + 6H2O → 3Be(OH)2 + 2NH3
    AlN + 3H2O → Al(OH)3 + NH3