Problem 32 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Give reason of the following: \(\mathrm{BeCl}_{2}\) can be easily hydrolysed.

Step-by-Step Solution

Answer

BeCl2 is easily hydrolysed because it is electron-deficient and forms stable hydrolysis products with water.

Step 1: Understanding Hydrolysis

Hydrolysis is a reaction that involves breaking chemical bonds with water. For a compound to undergo hydrolysis, it usually needs to have bonds that can be easily broken by water.

Step 2: Identify the Bond Type in BeCl2

Beryllium chloride ( BeCl_2 ) is a covalent compound because the electronegativity difference between Be and Cl is not high enough to form an ionic bond. This makes the Be - Cl bonds more susceptible to hydrolysis.

Step 3: Check for Electron Deficiency

Beryllium, being a group 2 element, usually forms compounds where it is in a +2 oxidation state. It has only four electrons in its valence shell, making BeCl_2 electron-deficient and thus reactive with water, which can donate electrons to stabilize Be .

Step 4: Role of Water in Hydrolysis

Water can act as a nucleophile, where it donates an electron pair to Be^{2+} . This interaction facilitates the breaking of Be - Cl bonds in the presence of water.

Step 5: Stability of Hydrolysed Products

Once BeCl_2 is hydrolysed, Be(OH)_2 and HCl are formed. Both of these products are more stable compared to the reactants in the presence of water, favoring the hydrolysis process.

Key Concepts

Electronegativity

Electronegativity is a measure of an atom's ability to attract and hold onto electrons within a bond. It's a crucial concept that affects the type of bonds between atoms and the properties of compounds. In the case of beryllium chloride \( \text{BeCl}_2 \), we see that the beryllium atom and chlorine atom come together to form a compound.
The electronegativity difference between beryllium \( \text{Be} \) and chlorine \( \text{Cl} \) is not very high. This moderate difference means that the bond formed between \( \text{Be} \) and \( \text{Cl} \) is more covalent rather than ionic.
When bonds have significant differences in electronegativity, they tend to become ionic. In contrast, a lower difference means a covalent bond, which can be more susceptible to interactions with water, such as hydrolysis.

Covalent Bonds

Covalent bonds are formed when two atoms share a pair of electrons. This sharing allows each atom to achieve a more stable electron configuration, usually resembling the nearest noble gas. In \( \text{BeCl}_2 \), each chlorine atom shares one electron with beryllium.
Sharing electrons allows the bonded atoms to fill their outer electron shells, which is the driving force for bond formation. Covalent bonds can range in strength and type, but they are generally stronger than ionic bonds regarding one-to-one interactions. Still, when water interacts, covalent bonds in \( \text{BeCl}_2 \) can be vulnerable if other factors, such as electron deficiency, play a role.
This type of bond ensures the compound's integrity, yet it can also determine how the compound interacts with other substances, such as in hydrolysis, where water breaks these covalent bonds.

Electron Deficiency

Electron deficiency occurs when an atom does not have a full complement of electrons to achieve a stable electronic configuration. This is quite apparent in molecules like \( \text{BeCl}_2 \).
Beryllium, in its compounds, typically features only four electrons shared in its bonding interactions, two from each chlorine atom, rather than the full octet that most chemists use as a benchmark for stability in main group elements.
This deficiency makes \( \text{Be} \) a sort of electron "sink", eager to accept electron pairs from other atoms. When water is present, it can donate an electron pair to \( \text{Be} \), facilitating the hydrolysis reaction by breaking the \( \text{Be-Cl} \) covalent bonds.
The reactivity of electron-deficient molecules like \( \text{BeCl}_2 \) underscores why they are more prone to undergoing further chemical reactions, paving the way to form more stable substances like \( \text{Be(OH)}_2 \) and \( \text{HCl} \). This electron deficiency is a key factor in understanding why compounds undergo certain reactions such as hydrolysis.