Question

In which form does \(BeCl_{2}\) exist in the solid state, vapor state and high temperature?
(1) Polymeric, Dimeric, Monomeric
(2) Dimeric, Polymeric, Monomeric
(3) Monomeric, Dimeric, Polymeric
(4) Polymeric, Monomeric, Dimeric

Answer 1

Beryllium Chloride Structure Analysis 

\( \text{BeCl}_2 \) exhibits different structures depending on the phase and temperature:

Solid State:

In the solid state, \( \text{BeCl}_2 \) exists as a polymeric structure. Beryllium has a tendency to form coordinate covalent bonds due to its small size and relatively high charge density. In the polymeric structure, each beryllium atom is bonded to four chlorine atoms, and each chlorine atom bridges between two beryllium atoms, forming a chain-like structure.

Vapour Phase:

In the vapour phase, below 1200 K, \( \text{BeCl}_2 \) primarily exists as a dimer (\( \text{Be}_2\text{Cl}_4 \)). The dimeric structure is formed through chloro-bridging, where two chlorine atoms bridge between two beryllium atoms. This satisfies the beryllium's desire for a coordination number of four.

Very High Temperature (above 1200 K):

At very high temperatures (above 1200 K), the thermal energy is sufficient to break the chloro bridges in the dimer, leading to the formation of monomeric \( \text{BeCl}_2 \) units. The monomeric form has a linear structure with beryllium having a coordination number of two.

Conclusion:

Therefore, the structures of \( \text{BeCl}_2 \) are polymeric in the solid state, dimeric in the vapour phase, and monomeric at very high temperatures.