Question

Discuss the preparation, properties and structure of \(\mathrm{BeCl}_{2}\).

Short answer

Beryllium Chloride can be prepared through the reaction of beryllium metal with chlorine gas. It's a deliquescent white solid with a high melting point and is soluble in water. In its gaseous state, BeCl2 is linear with a 180-degree bond angle due to its two bonding pairs. However, in its solid state, it forms a polymer structure with a tetrahedral geometry.

Step-by-step solution

Preparation of BeCl2

Beryllium chloride, BeCl2, can be prepared by reaction of beryllium metal with chlorine gas. The reaction is as follows: \[ Be + Cl_2 \rightarrow BeCl_2 \]. Beryllium metal reacts with chlorine gas to form beryllium chloride.

Properties of BeCl2

Beryllium chloride is a white solid with a high melting point (405 C) and it is soluble in water. It's a deliquescent compound, meaning it can absorb water from the atmosphere. In the gaseous phase, BeCl2 exists as a linear molecule. In its solid state, BeCl2 forms a polymer structure.

Structure of BeCl2

In the gaseous phase, BeCl2 is linear with a 180-degree bond angle. This is because beryllium has two bonding pairs and no lone pairs, so these pairs try to get as far apart as possible, resulting in a linear molecule. In the solid phase, BeCl2 forms a polymer structure, where each Be is coordinated to four Cl atoms, thus forming a tetrahedral geometry. The hybridization of Be in BeCl2 is sp.

Key concepts

Preparation of BeCl2

The synthesis of Beryllium Chloride (BeCl2) is a fundamental process in inorganic chemistry that involves the direct combination of beryllium metal with chlorine gas. The chemical reaction is succinctly represented by the equation:
\[ Be + Cl_2 \rightarrow BeCl_2 \].
During the reaction, which is typically conducted at high temperatures, beryllium metal atom reacts vigorously with molecules of chlorine gas to form the ionic compound BeCl2. It's important to handle the reactants and the product with care, as they are hazardous materials. Variables like temperature, pressure, and the purity of the beryllium metal can affect the yield and quality of the produced beryllium chloride.

Properties of BeCl2

Beryllium chloride distinguishes itself by several notable properties that are crucial to understand its reactivity and applications. This white solid has a high melting point of about 405°C, indicative of its strong ionic bonds. Remarkably, BeCl2 is soluble in water; however, it is a deliquescent compound, which means it has the ability to absorb moisture from the environment and dissolve in it. That's why BeCl2 needs to be stored in airtight containers to prevent it from becoming a hydrated form. In the gaseous phase, beryllium chloride takes form as a discrete linear molecule leading to its unique physical and chemical behavior that differs from its state in the solid phase.
Moreover, due to its polar nature, BeCl2 can act as a Lewis acid, forming complexes with donor molecules. When dissolved in water, it can hydrolyze to give hydrochloric acid and species of beryllium hydroxide, which should be noted given the toxicity of beryllium compounds.

Structure of BeCl2

The structure of BeCl2 varies markedly between its gaseous and solid states due to different bonding schemes. In the gaseous phase, the molecule adopts a linear shape, which can be attributed to the electronic configuration of beryllium. With just two bonding pairs and no lone pairs of electrons, the electron cloud around beryllium is shaped to minimize repulsion, thus arranging the chlorides opposite each other and producing a bond angle of 180 degrees.
In its solid state, BeCl2 displays a more complex polymeric structure. Here, each beryllium atom becomes surrounded by four chlorine atoms, leading to a coordination number of four and a tetrahedral coordination geometry. This polymeric chain structure accounts for BeCl2's high melting point and solidity. The bonds within the polymer are covalent in nature with partial ionic character, and the hybridization state of beryllium in this compound is described as sp. It is essential to understand this dual behaviour in order to grasp the versatility of BeCl2 in different physical contexts and its implications for chemical reactions.