Question

The molecule having largest dipole moment among the following is: (a) \(\mathrm{CHI}_{3}\) (b) \(\mathrm{CH}_{4}\) (c) \(\mathrm{CHCl}_{3}\) (d) \(\mathrm{CCl}_{4}\)

Short answer

The molecule with the largest dipole moment is \(\mathrm{CHCl}_{3}\).

Step-by-step solution

Understanding Dipole Moment

The dipole moment is a measure of the separation of charge in a molecule. It quantifies the polarity of a molecule; molecules with polar bonds and an asymmetrical shape will generally have a higher dipole moment.

Analyzing Molecular Structure

Let's examine the structures:- (a) \(\mathrm{CHI}_{3}\) has polar C-I bonds, but the symmetrical shape may reduce overall dipole moment. - (b) \(\mathrm{CH}_{4}\) is completely symmetrical and non-polar, resulting in a dipole moment of zero. - (c) \(\mathrm{CHCl}_{3}\) has an asymmetrical structure with polar C-Cl bonds.- (d) \(\mathrm{CCl}_{4}\) is symmetrical and the bond dipoles cancel out, making it non-polar.

Determining Highest Dipole Moment

Evaluate the dipole moments based on symmetry and polarity:- (a) \(\mathrm{CHI}_{3}\) could have a dipole moment, but its symmetry reduces it.- (b) \(\mathrm{CH}_{4}\) is non-polar.- (c) \(\mathrm{CHCl}_{3}\), being asymmetrical with polar C-Cl bonds, has a significant dipole moment.- (d) \(\mathrm{CCl}_{4}\) is non-polar due to symmetry.Thus, \(\mathrm{CHCl}_{3}\) has the largest dipole moment.

Key concepts

Polarity of Molecules

The polarity of a molecule refers to the distribution of electrical charge over the atoms involved. This determines whether a molecule is polar or non-polar. A polar molecule arises when there is an uneven distribution of electrons between the nuclei of the bonded atoms. This can occur in two major scenarios: when different atoms with varying electronegativities form a bond, or when the molecular shape does not balance out the dipoles.
For example, let's consider a water molecule. Its V-shape and electronegative oxygen create a region with a partial negative charge and the hydrogen atoms exhibit partial positive charges. Thus, water is a highly polar molecule. In contrast, molecules like methane (\( ext{CH}_4\)) have an equal distribution of charge due to the symmetrical arrangement and similar electronegativity among hydrogen atoms and the central carbon atom, making it non-polar.

• Polar molecules have significant dipole moments due to the separation of charges.
• Non-polar molecules maintain a balanced charge distribution and have no net dipole moment.
• The overall polarity affects how molecules interact with electric fields and other molecules.

Symmetrical vs Asymmetrical Structures

The shape of a molecule greatly influences its polarity. Molecules can be either symmetrical or asymmetrical, and this can determine whether bond dipoles cancel out or reinforce each other.
In symmetrical structures, such as in carbon tetrachloride (\( ext{CCl}_4\)), the molecule's shape is such that the individual bond dipoles cancel each other out. This is due to an even distribution around the central atom, resulting in no overall dipole moment. Symmetrical arrangements often lead to non-polar molecules.
On the other hand, asymmetrical structures like chloroform (\( ext{CHCl}_3\)) have a shape where the dipoles from polar bonds do not cancel because they are not evenly distributed. This creates areas of partial charges, making the molecule polar and leading to a higher dipole moment.

• Symmetrical structures often lead to non-polar molecules because dipoles cancel out.
• Asymmetrical structures have a higher likelihood of being polar and having a net dipole moment.
• The shape affects how molecules interact with each other due to the presence or absence of polar interactions.

Polar vs Non-Polar Bonds

Understanding the type of bonds within molecules is crucial for determining molecular polarity. In essence, bonds can be categorized into polar and non-polar types.
In polar bonds, atoms with different electronegativities share electrons unequally. The more electronegative atom attracts the electrons more strongly, creating a dipole. Chlorine is more electronegative than carbon, so C-Cl bonds in chloroform (\( ext{CHCl}_3\)) are polar.
Non-polar bonds occur between atoms with similar electronegativities, sharing electrons equally. In methane (\( ext{CH}_4\)), the C-H bonds are considered non-polar due to similar electronegativity values causing no separation of charge.

• Polar bonds have a positive and a negative end, creating molecular dipoles.
• Non-polar bonds generally do not create distinct charge ends, leading to a neutral molecule.
• While polar bonds contribute to molecular polarity, the overall molecular structure determines the final polarity status.