Problem 46 - A Complete Resource Book in Chemistry for JEE Main

Question

Carbon tetrachloride does have not dipole moment because of (a) its planar structure (b) its regular tetrahedral structure (c) similar sizes of carbon and chlorine atoms (d) similar electron affinities of carbon and chlorine

Step-by-Step Solution

Answer

(b) its regular tetrahedral structure

Step 1: Understanding Dipole Moment

A molecule's dipole moment is determined by the separation of electrical charges. A molecule will have a net dipole moment if there is a significant difference in electronegativity between its atoms and if it lacks symmetry.

Step 2: Analyzing Carbon Tetrachloride Structure

Carbon tetrachloride (CCl_4) consists of one carbon atom bonded to four chlorine atoms. The molecule has a tetrahedral geometry, which is a symmetrical shape.

Step 3: Tetrahedral Symmetry and Dipole Moment

Due to its tetrahedral structure, the dipoles between the carbon atom and each chlorine atom cancel each other out. This cancelation occurs because the dipoles point in opposite directions, resulting in no net dipole moment.

Key Concepts

Carbon Tetrachloride Structure

Carbon tetrachloride, commonly represented as \( \text{CCl}_4 \), is a fascinating molecule due to its unique arrangement of atoms. At the center, you have a single carbon atom that forms the backbone of the structure. This carbon is surrounded symmetrically by four chlorine atoms. Each chlorine atom is connected directly to the carbon, forming single covalent bonds.
These carbon-chlorine bonds are crucial in defining the properties of carbon tetrachloride. It's important to remember that while the individual bonds are polar due to the difference in electronegativity between carbon and chlorine, the overall structure of the molecule can influence whether it has a dipole moment or not.
Understanding the spatial arrangement in \( \text{CCl}_4 \) allows us to appreciate why this compound behaves the way it does, particularly when it comes to properties such as boiling point, solvent capabilities, and, of course, dipole moment.

Tetrahedral Symmetry

The shape of the \( \text{CCl}_4 \) molecule is described as tetrahedral. This tetrahedral geometry is a key feature because it contributes significantly to the molecule's overall behavior and characteristics.
In a tetrahedral structure, the carbon atom is situated at the center with the chlorine atoms at the corners of a tetrahedron. This geometric arrangement is perfectly symmetrical. The angles between any two bonds (the bond angle) are roughly 109.5 degrees.

• This symmetry means that any dipole moments due to the C-Cl bonds are balanced.
• The chlorine atoms are so distributed that they effectively cancel out each other's dipole moments.

This balance and symmetry lead to no net dipole moment, rendering \( \text{CCl}_4 \) a non-polar molecule despite the differences in individual bond polarities.

Electronegativity

Electronegativity is a measure of an atom's ability to attract shared electrons within a chemical bond. In \( \text{CCl}_4 \), this concept is pivotal as it determines the polarity of each C-Cl bond.

• Chlorine is more electronegative than carbon. This means that in a C-Cl bond, chlorine will attract the shared electrons closer to itself.
• This attraction makes each individual C-Cl bond polar because there is a distinct separation of charge between the carbon and chlorine atoms, with chlorine being partially negative and carbon being partially positive.

However, the tetrahedral symmetry ensures that any bond polarity is evenly distributed and thus cancels out, eliminating any overall dipole moment. Hence, while electronegativity contributes to polar bonds, it is the structural symmetry that ultimately determines the lack of a net dipole moment in \( \text{CCl}_4 \).