Peculiar Behaviour of Beryllium:
Beryllium is the s-block element of the modern periodic shows some differences from the rest of the members of its family.
The electronic configuration of Beryllium is 1s2 2s2
The anomalous properties of beryllium is especially due the following reasons:
- small size
- high electronegativity
- high ionization energy
- high polarizing power
(i) Beryllium atom is very small so according to Fajan’s rule which states that small highly charged cations tend to form polar covalent compounds thus its compounds are somewhat covalent.
(ii) Beryllium is as hard as iron while the other members of the alkaline earth metals are soft.
(iii) Melting and boiling point of Beryllium is much higher than other members of its family.
(iv) Halides of Beryllium are soluble in organic solvents while others are soluble in water.
(v) Oxide and hydroxide of Beryllium are amphoteric while that of others is basic.
Be(OH)2 + 2HCl → BeCl2 + 2H2O
Be(OH)2 + 2NaOH → Na2[Be(OH)4]
(vi) It is the only member of the family which in reaction with alkalis liberates hydrogen.
Be + 2NaOH → Na2BeO2 + H2
(vii) Beryllium resistant complete oxidation due to presence of BeO coating.
(viii) It does not react even with boiling water.
(ix) Oxides, nitrides, sulphides, chlorides etc of group II-A are ionic but that of Be are covalent.
Explanation:
The polarizing power of both Be2+ as well as that of Cl– ion is so high. So Be2+ sufficiently pulls electrons from Cl– ion, such that electron pair is effectively shared. This is the reason that BeCl2 is covalent. This is following Fajan,s rule.
(x) Alkaline earth metals impart color to flame but Be does not impart any color to the flame.
(xi) Oxide of Be is insoluble in water.
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Electronic Configuration of Beryllium
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