Structures of Beryllium Chloride in the Solid State and Vapour Phase

Structure of Beryllium Chloride

• All metals on heating with halogens from halides of type MX₂M+X2→MX2
• BeCl₂ cannot be prepared in aqueous solution due to the formation of hydrated ion [Be(H₂O)₄]²⁺.
• BeCl₂ can be prepared by heating BeO in the presence of coke in a current of chlorine gas.
• Structure of BeCl₂
  • In Solid State:
    
  • In Liquid State: Two forms of BeCl₂ exist at different temperature. Above 1200K, a monomeric form exists as shown below.
    
    Below 1200K, dimeric form exists as shown below.
    

A "covalent alkaline earth metal halide" refers to a compound composed of an alkaline earth metal (Group 2 elements like beryllium, magnesium, calcium, etc.) and a halogen (Group 17 elements like fluorine, chlorine, bromine, iodine, etc.) in which the bonding involves the sharing of electron pairs between the metal and the halogen atoms, indicating a covalent bond.

These compounds typically form when the electronegativity difference between the metal and halogen atoms is not significant enough to warrant a complete transfer of electrons, leading to a shared electron pair between the atoms. Examples include beryllium fluoride (BeF₂), magnesium chloride (MgCl₂), and calcium bromide (CaBr₂). These compounds often have high melting and boiling points due to the strong directional covalent bonds between the metal and halogen atoms, and they may exhibit some degree of solubility in polar solvents due to their polar nature.

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Solved Examples

Example:1

Q 1. The structure of beryllium chloride in the solid state and vapour phase, respectively, are :

1) Chain and chain

2) Dimeric and dimeric

3) Chain and dimeric

4) Dimeric and chain

Solution-
As we learned-

Structure of Beryllium chloride in vapour and solid phase. -

A. In vapour state, it exists as a chlorine bridge dimer.

B. In the solid state, BeCl₂ has a polymeric structure with chlorine bridges.

BeCl₂ is an electron-deficient compound with sp hybridization. Therefore in the solid state, it combines with another BeCl₂ molecule to give Be₂Cl₄ by forming a coordinate bond between Cl and Be thus attaining more stability

However, in the gaseous state, it exists as a single molecule. At room temperature BeCl₂ is a polymeric solid, this is because it can form coordinate bonds with other molecules of the same type and forms a chain-like structure.

Therefore, option(3) is correct.

Example :2

Q.2 The covalent alkaline earth metal halide (X=Cl, Br,I) is:

1) MgX₂

2) CaX₂

3) BeX₂

4) SrX₂

Solution-

As we learned

Covalent alkaline earth metal halide:-

In chemical terms, all of the alkaline earth metals react with the Halogens to form the alkaline earth metal halides, all of which are ionic crystalline compounds except for Beryllium halide, which is a covalent [exception. BeCl₂].

A chain type of structure can be observed in the solid form of beryllium chloride.

These beryllium halides can be generally dissolved in organic solvents.

Hence, the answer is the option (3).

Conclusion

Beryllium chloride (BeCl₂) is a useful chemical for competitive examinations and applications in chemistry since it possesses distinct structural features in different phases. In the solid state, BeCl₂ forms a polymeric chain structure when beryllium atoms are linked to create a one-dimensional chain with significant covalent character. Each beryllium atom has a tetrahedral coupling to four chlorine atoms. BeCl₂ is observed as discrete linear molecules with sp hybridization and predominantly covalent bonding in the gas phase. The hydrated ion [Be(H₂O)₄]²⁺ is produced during the heating of BeO in the presence of coke and chlorine gas, rendering the production of BeCl₂ in an aqueous solution unfeasible. BeCl₂ exists as a monomeric form above 1200K and as a dimeric form below 1200K.