Problem 40 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The \(\mathrm{Cl}-\mathrm{C}-\mathrm{Cl}\) angle in \(1,1,2,2\)-tetrachloroethene and tetrachloromethane respectively will be about (a) \(120^{\circ}\) and \(109.5^{\circ}\) (b) \(90^{\circ}\) and \(109.5^{\circ}\) (c) \(109.5^{\circ}\) and \(90^{\circ}\) (d) \(109.5^{\circ}\) and \(120^{\circ}\)

Step-by-Step Solution

Answer

Option (a): 120° and 109.5°.

Step 1: Determine the molecular geometry of 1,1,2,2-tetrachloroethene

1,1,2,2-tetrachloroethene (C_2Cl_4) features a double bond between the two carbon atoms. This compound has a nearly planar geometry due to the sp\(^2\) hybridization, leading to bond angles close to \(120^\circ\).

Step 2: Determine the molecular geometry of tetrachloromethane

Tetrachloromethane (CCl_4) has a central carbon atom tetrahedrally surrounded by chlorine atoms. The geometry of this compound is tetrahedral, with bond angles around \(109.5^\circ\) due to sp\(^3\) hybridization.

Step 3: Compare given answer choices to the bond angles derived

After analyzing the geometries, we find that the \(Cl-C-Cl\) angle in 1,1,2,2-tetrachloroethene is close to \(120^\circ\) and in tetrachloromethane it is \(109.5^\circ\). Upon reviewing the options, option (a) matches these calculated bond angles: \(120^\circ\) and \(109.5^\circ\).

Key Concepts

Bond Angles

Bond angles are a critical concept in molecular geometry, influencing the shape and reactivity of molecules. A bond angle is the angle formed between three atoms across at least two bonds. In simpler terms, if you imagine a molecule's structure as a framework, the bond angle is the figure that tells you how those parts are positioned relative to each other. For example, the

• VSEPR Theory: This stands for Valence Shell Electron Pair Repulsion theory, and it's used to predict the geometry of molecules. It operates on the principle that electron pairs will position themselves as far apart as possible to minimize repulsion.
• Impact of Different Hybridizations: When atoms form molecules, the types of hybridization will affect bond angles. For example, in an sp t³ hybridization typical of a tetrahedral geometry, the bond angles are around 109.5°. In contrast, sp t² hybridization, often seen in planar geometries, results in bond angles of about 120°.

Understanding bond angles allows chemists and students to infer the geometry and potential reactivity of the molecules, which is essential in fields like drug design and materials science.

sp2 Hybridization

The sp t² hybridization is a fascinating concept in chemistry. It occurs when one s and two p orbitals combine to form three hybrid orbitals. These orbitals arrange themselves in a planar triangular shape, each separated by an angle of roughly 120°. This hybridization is common in compounds containing double bonds, such as alkenes.

• Planar Geometries: In molecules like 1,1,2,2-tetrachloroethene, the carbons are sp t² hybridized. This imparts a planar geometry to the molecule, which is a contrast to a tetrahedral geometry.
• Importance in Reactivity: The presence of sp t² hybridization affects how reactive a molecule is. The molecule's flat shape allows for better overlap during reactions, influencing the molecule's properties and interactions.

The ability to recognize sp t² hybridization is essential for understanding double-bonded systems. This helps predict the geometry and also impacts how it might interact in chemical reactions.

sp3 Hybridization

The sp t³ hybridization involves the combination of one s orbital and three p orbitals to form four equivalent hybrid orbitals. This form of hybridization results in a tetrahedral molecular geometry, with bond angles of approximately 109.5°. A classic example is methane (CH t₄), but it's also seen in tetrachloromethane (CCl ₄).

• Characteristics: The sp t³ hybridized molecules are three-dimensional, creating a more spatially distributed structure. This geometry is key in defining the compactness and the overall reactivity of the molecules.
• Applications in Nature and Industry: Understanding sp t³ hybridization aids in predicting reactions in which these molecules participate. For instance, enzymes that require specific molecular fits often rely on the geometry provided by sp t³ hybridization.

Grasping the concept of sp t³ hybridization is vital for students studying organic chemistry as it underpins many structural and functional attributes of organic reactions.