Question

Which among the following statements is correct? (1) In the solid state ${\mathrm{BeCl}}_2$ has a polymcric chain structure and contains three centred bonds. (2) In the vapour state ${\mathrm{BeCl}}_2$ exists as a dimer. (3) ${\mathrm{BeCl}}_2$ is a covalent compound soluble in organic solvents. (4) $\mathrm{\Lambda }$ ll are correct.

Short answer

All are correct (Option 4).

Step-by-step solution

- Analyze the solid state

In the solid state, ${\mathrm{BeCl}}_2$ forms a polymeric chain structure. The beryllium atoms are each bonded to two chlorine atoms and share chloride bridges forming a three-center bond.

- Analyze the vapour state

In the vapour state, ${\mathrm{BeCl}}_2$ does not exist as a monomeric molecule. Instead, it forms dimers $({\mathrm{BeCl}}_2{)}_2$, where two ${\mathrm{BeCl}}_2$ molecules are linked through chlorine bridges.

- Check solubility and bonding

${\mathrm{BeCl}}_2$ is a covalent compound due to the high charge density of the beryllium ion. It is soluble in organic solvents, which typically dissolve covalent compounds.

- Interpret the options

Examine each option: \ 1. True, ${\mathrm{BeCl}}_2$ has a polymeric chain structure with three-center bonds in the solid state. \ 2. True, ${\mathrm{BeCl}}_2$ exists as a dimer in the vapour state. \ 3. True, ${\mathrm{BeCl}}_2$ is a covalent compound and is soluble in organic solvents. \ 4. True, all the statements are correct.

Key concepts

solid-state chemistry

Solid-state chemistry examines compounds in their solid state, where the atoms or ions are arranged in an organized structure. In solid-state, ${\text{BeCl}}_2$ forms an intricate pattern due to the interactions between its particles. Rather than existing as isolated molecules, ${\text{BeCl}}_2$ adopts a more complex arrangement, influencing its properties significantly.

polymeric chain structure

Solid ${\text{BeCl}}_2$ features a polymeric chain structure. This means repeated units of ${\text{BeCl}}_2$ are connected, forming long chains. Each beryllium atom bonds with two chlorine atoms directly and connects with other beryllium atoms via shared chlorine atoms. So, the structure extends, forming a macromolecule. This polymeric structure stabilizes ${\text{BeCl}}_2$ and gives it distinctive properties in its solid form.

three-center bonds

A unique feature of solid ${\text{BeCl}}_2$ is the presence of three-center bonds. In these bonds, two electrons are shared among three atoms, which in this case are typically two beryllium atoms and one chlorine atom. This bonding type is somewhat unusual and helps to explain the stability and formation of the polymeric chains in solid ${\text{BeCl}}_2$. It's a crucial concept for understanding the compound's structure.

dimer formation

Upon heating, ${\text{BeCl}}_2$ transitions to the vapor state, and its behavior changes. Instead of existing as individual molecules, ${\text{BeCl}}_2$ forms dimers. A dimer consists of two ${\text{BeCl}}_2$ units connected through chlorine atoms. This formation (\text{BeCl}_2)_2 is more stable than two separate ${\text{BeCl}}_2$ molecules due to the sharing of electrons. This structural change is important in the gaseous state.

covalent compounds

${\text{BeCl}}_2$ is classified as a covalent compound. Covalent bonds involve the sharing of electron pairs between atoms. The high charge density of beryllium makes its bonding more covalent than ionic. Therefore, ${\text{BeCl}}_2$ does not form ions in solution but remains as distinct molecules sharing electrons.

solubility in organic solvents

One notable property of ${\text{BeCl}}_2$ is its solubility in organic solvents. Organic solvents like alcohol, ether, or benzene can dissolve ${\text{BeCl}}_2$, which is unusual for many salts. This solubility is due to its covalent nature, allowing it to interact well with the non-polar structures of organic compounds, indicating useful chemical behavior in various applications.