Question

Which one of the following has the highest dipole moment? (i) \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\) (ii) \(\mathrm{CHCl}_{3}\) (iii) \(\mathrm{CCl}_{4}\)

Short answer

\(\mathrm{CH}_{2} \mathrm{Cl}_{2}\) has the highest dipole moment.

Step-by-step solution

Understanding Dipole Moments

A dipole moment arises from differences in electronegativity between atoms in a molecule. Molecules with higher electronegativity differences typically have higher dipole moments. Additionally, the molecule's symmetry affects whether dipole moments cancel each other out or add up.

Analyzing Each Molecule

Let's look at each molecule:(i) \(\mathrm{CH}_2 \mathrm{Cl}_2\) contains two chlorine atoms and two hydrogen atoms bonded to a central carbon. The molecule is not symmetrical, leading to a net dipole moment.(ii) \(\mathrm{CHCl}_3\) has three chlorine atoms and one hydrogen atom. The shape creates some symmetry, but the polarity of the molecules is significant.(iii) \(\mathrm{CCl}_4\) is symmetrical with four chlorine atoms, leading to the cancellation of dipole moments and resulting in zero net dipole moment.

Determining Electronegativity and Shape

The presence and arrangement of chlorine atoms (which are more electronegative than hydrogen) significantly influences dipole moments. \(\mathrm{CHCl}_3\) has a slightly lesser symmetric shape compared to \(\mathrm{CH}_2 \mathrm{Cl}_2\), which leads to a greater dipole moment in \(\mathrm{CH}_2 \mathrm{Cl}_2\).

Conclusion on Highest Dipole Moment

Given the asymmetrical shape and arrangement of atoms, \(\mathrm{CH}_2 \mathrm{Cl}_2\) has the highest dipole moment of the three options. The molecular geometry ensures that the dipoles do not completely cancel, resulting in a higher net dipole moment.

Key concepts

Electronegativity

Electronegativity is a fundamental concept in chemistry, relating to the ability of an atom to attract electrons towards itself when it forms a bond with another atom. This property plays a crucial role in determining the dipole moment of a molecule. The larger the difference in electronegativity between two bonded atoms, the more polar the bond becomes, resulting in a higher dipole moment. For example, chlorine is significantly more electronegative than hydrogen.
Hence, in molecules such as HCH₂(Cl)₂ and HCCl₃ , the chlorine atoms draw electron density towards themselves, leading to a polarization of bonds.
When we compare different molecules, those with greater electronegativity differences among atoms tend to have larger dipole moments.
- Chlorine's high electronegativity makes it a common contributor to dipole moments in organic molecules. - Electronegativity tends to increase across a period and decrease down a group in the periodic table. Understanding electronegativity helps predict molecular behavior in reactions and interactions with other compounds.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. This geometry is crucial because it influences the overall dipole moment. For instance, linear, tetrahedral, and trigonal pyramidal shapes each exhibit different behaviors when it comes to dipole neutrality or tip-offs. Let's consider the examples given: - CH₂Cl₂ (dichloromethane) has a tetrahedral arrangement around the central carbon atom. However, because it is not symmetric, the electronegative chlorine atoms lead to a high net dipole moment. - CHCl₃ (chloroform) also presents a tetrahedral shape but with less symmetry compared to CCl₄ , where four chlorine atoms surround the central carbon symmetrically, leading to dipole moment cancellation. - In symmetrical molecules such as CCl₄ , the dipoles cancel out due to equal and opposite dipole vectors. - Asymmetrical molecules with polar bonds typically result in non-zero dipole moments. Understanding molecular geometry can be pivotal when predicting molecular interactions and reactivity, as it provides insights into the molecule's polarity.

Symmetry in Molecules

Symmetry in molecules greatly impacts their dipole moments. A molecule with symmetric geometry is likely to have dipoles that cancel each other out, resulting in a net dipole moment of zero. Conversely, asymmetrical molecules often exhibit non-zero dipole moments due to the inability of the dipoles to cancel completely.
Let's delve deeper: - Symmetric structures like CCl₄ are tetrahedral but perfectly symmetrical, so their dipole moments balance, leading to no net dipole moment. - Asymmetry, as seen in CH₂Cl₂ , prevents the complete cancelation of individual bond dipoles, hence a non-zero net dipole moment. - Molecular symmetry affects physical properties like boiling and melting points, solubility, and reactivity. Understanding symmetry helps chemists predict how molecules will interact with each other and other substances, almost acting as a compass for molecular behavior in different environments. Overall, recognizing and analyzing molecular symmetry is essential for understanding the physical and chemical properties of molecules.