An oxide of allkaline earth metals \((X)\) reacts with \(\mathrm{C}\) and \(\mathrm{Cl}_{2}\) to give a compound \(Y . Y\) is found in polymeric chain structure and is electron deficient molecule. The compound \(Y\) is (a) \(\mathrm{BeO}\) (b) \(\mathrm{BeCl}_{2}\) (c) \(\mathrm{Be}(\mathrm{OH})_{2}\) (d) \(\mathrm{BeCO}_{3}\)

Beryllium chloride, or BeCl₂, is a fascinating compound that students encounter in alkaline earth metals chemistry. It stands out due to its distinctive properties and behaviors, specifically its ability to form a polymeric chain structure and act as an electron-deficient compound. When beryllium, the lightest of the alkaline earth metals, reacts with chlorine, the result is beryllium chloride. This reaction is a fine example of transforming an oxide form of an element into a chloride by a halogenation process.

In educational settings, this compound provides a great opportunity to discuss the variations in chemical behaviors among the alkaline earth metals. While magnesium chloride and calcium chloride, for example, form simple ionic structures, BeCl₂ differs significantly due to beryllium's small atomic and ionic sizes, allowing it to participate in the formation of covalent bonds. This covalent bonding leads to the formation of structures that are not typically ionic but have directional properties, as reflected in BeCl₂'s polymeric chain structure.

Electron-deficient compounds are a critical concept in chemistry that refers to molecules or ions which have fewer electrons than required for a complete set of covalently bonded electron pairs around the atomic centers. These compounds often form structures that defy the conventional octet rule. Beryllium chloride is such a molecule. In the context of beryllium chloride, the beryllium atom does not achieve a complete octet of electrons in its valence shell through its bonds with chlorine atoms.

This deficiency in electrons is what leads to the formation of electron-deficient bridges where two chlorine atoms can share a single pair of electrons with a beryllium atom, facilitating the extension of the structure into a polymer. The concept of electron-deficiency is essential for understanding the reactivity and bonding of compounds involving small, highly charged atoms like beryllium. It's also crucial in discussions relating to Lewis acids, where electron pair acceptance is a foundational property.

The polymeric chain structure is a special form of molecular arrangement where similar units, known as monomers, link together in long, repeating chains. In the case of BeCl₂, this structure is particularly intriguing because its chains are not made up of identical monomers, but rather repeat units formed by the bridging of atoms.

When students learn about polymeric structures, they often start with organic polymers, like polyethylene, where long carbon chains form the backbone. However, inorganic polymers like BeCl₂ can provide a fresh perspective on the diversity of polymeric forms. For BeCl₂, the polymeric chains comprise a series of beryllium atoms covalently bonded to chlorine atoms, which serve as bridges between beryllium centers.

• The chlorine atoms act as links, expanding the structure one-dimensionally.
• This chain-like structure results from the electron-deficiency of beryllium, as it needs to share electrons with multiple chlorines to approach a stable configuration.
• The polymeric chains of BeCl₂ are an excellent example of how molecular geometry and electron distribution can lead to diverse and complex structures in chemistry.