ANOMALOUS BEHAVIOUR OF BERYLLIUM

• 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. Be₃N₂ is covalent rest of the nitrides are ionic.

Beryllium has a unique chemical behaviour due to its:

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

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 + H₂OBeO + 2NaOH → Na₂BeO₂ + H₂O
  Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂OAl₂O₃ + 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