Question

Draw the structure of (i) \(\mathrm{BeCl}_{2}\) (vapour) (ii) \(\mathrm{BeCl}_{2}\) (solid).

Short answer

In vapor, BeCl2 is linear; in solid, it's a polymeric chain.

Step-by-step solution

Understand BeCl2 in Vapour Phase

In the vapour phase, beryllium chloride ( BeCl_2 ) exists as a discrete molecule. Each Be atom is covalently bonded to two Cl atoms in a linear fashion. This occurs because Be can hybridize its orbitals to form sp hybrid orbitals, allowing it to bond at a 180-degree angle, making the structure linear.

Draw the Structure of Vapour Phase BeCl2

Represent BeCl2 in the vapour phase by drawing a linear molecule. Place Be in the center and bond two Cl atoms at either end: Cl-Be-Cl. Ensure the bond angles are 180 degrees to illustrate the linear shape.

Understand BeCl2 in Solid Phase

In the solid phase, BeCl_2 forms a polymeric chain structure. Each Be is tetrahedrally coordinated with Cl atoms. Connections are formed through bridging Cl atoms, resulting in a continuous chain. The coordination number increases due to the extended network.

Draw the Structure of Solid Phase BeCl2

To illustrate the polymeric chain structure, draw each Be atom bonded to four Cl atoms, two of which are terminal (not shared) and two are bridging Cl atoms that connect with adjacent Be atoms. This forms a continuous chain of connected tetrahedra.

Key concepts

Linear Molecular Geometry

In chemistry, understanding a molecule's geometry helps predict both its physical and chemical properties. One interesting example is beryllium chloride (\(\mathrm{BeCl}_{2}\)), which exhibits linear molecular geometry in its vapor phase. Beryllium in the center, flanked by two chlorine atoms, forms a straight line, making it linear, perfect for BeCl₂ vapor. Beryllium, in this case, undergoes

• sp hybridization: Beryllium's single 2s electron pairs with one 2p electron to form two sp hybrid orbitals,
• resulting in two equivalent linear bonds at a bond angle of 180 degrees, demonstrating the linear geometry.

This predictable bond angle maintains the molecule's linear geometry at all times, simplifying the visualization of its structure. As such, both bond length and molecular symmetry contribute to this simple yet critical characteristic of BeCl₂.

Polymeric Chain Structure

Unlike in the vapor phase, beryllium chloride behaves quite differently in its solid form. It arranges itself into a polymeric chain structure, showcasing a transformation in its molecular configuration. The notable feature of the polymeric chain structure is the continuous network of bonded atoms:

• In solid BeCl₂, each beryllium atom is surrounded by four chlorine atoms in a tetrahedral coordination,
• Out of these, two are terminal chlorines directly bonded to beryllium,
• While the other two are bridging chlorines that link to adjacent beryllium atoms.

This interconnected arrangement leads to a continuous chain structure. The increased coordination number hints at stronger interactions within the solid lattice, impacting physical properties like melting point and solubility. Understanding this transformation from simple to complex structures is crucial for comprehending how molecular architecture can influence material properties.

Hybridization

Hybridization is a key concept in explaining molecular shapes, particularly for compounds like beryllium chloride. In chemistry, hybridization refers to how atomic orbitals mix to form new hybrid orbitals, suitable for bonding. For the vapor form of BeCl₂:

• Beryllium starts with a 2s orbital and an empty 2p orbital,
• These orbitals undergo sp hybridization, producing two identical sp hybrid orbitals,
• This hybridization allows each Be atom to form two equal-length bonds with the chlorine atoms, resulting in linear geometry.

Meanwhile, in its solid form, BeCl₂ adopts a giant covalent structure, demanding different coordination through overlapping of larger sets of orbitals. Recognizing the role of hybridization aids in understanding how structures adapt based on the state of the matter and external influences, giving insight into its behavior in both gaseous and solid states.