Problem 103 - A Complete Resource Book in Chemistry for JEE Main

Question

If the molecule of \(\mathrm{HCl}\) was totally polar, the expected value of dipole moment was \(6.12 \mathrm{D}\) but the experimental value of dipole moment calculated was \(1.03\) D. Calculate the percentage ionic character. (a) 0 (b) 17 (c) 50 (d) 90

Step-by-Step Solution

Answer

The percentage ionic character is approximately 17%.

Step 1: Understand the Concept

The dipole moment (1D1D) is a measure of the polarity of a molecule. The percentage ionic character of a bond can be determined by comparing the observed dipole moment with the theoretical dipole moment if the bond were 100% ionic.

Step 2: Use the Formula for Percentage Ionic Character

The formula to calculate the percentage ionic character is given by:\[\text{Percentage Ionic Character} = \left( \frac{\text{Observed Dipole Moment}}{\text{Expected Dipole Moment}} \right) \times 100\] Where the observed dipole moment is 1.03 D and the expected dipole moment is 6.12 D.

Step 3: Plug Values into the Formula

Substitute the known values into the formula:\[\text{Percentage Ionic Character} = \left( \frac{1.03}{6.12} \right) \times 100\]Calculate this expression to find the result.

Step 4: Calculate the Result

Perform the calculation:\[\frac{1.03}{6.12} \approx 0.1683\]Therefore, the percentage ionic character is:\[0.1683 \times 100 \approx 16.83\]

Key Concepts

Understanding Dipole Moment

In chemistry, the dipole moment is an important concept that helps in determining how polar a molecule is. Essentially, it quantifies the electric polarity of a molecule, which is formed due to the difference in electronegativity between atoms. When two atoms form a bond and have different electronegativities, they don't share electrons equally, resulting in a dipole moment. This moment is represented by the symbol Debye (D) and reflects how much charge separation exists in the bond.

Some key points about dipole moments include:

• A larger dipole moment indicates a more significant degree of polarity in the molecule.
• If there is a complete charge separation (100% ionic character), the molecule will have a high dipole moment.
• For example, in the molecule HCl, because chlorine is more electronegative than hydrogen, there is a noticeable dipole, where electrons are shifted more towards the chlorine atom, creating a polar molecule.

Understanding the dipole moment helps us predict the behavior of molecules in an electric field and gives insights into molecular interactions.

Calculating Percentage Ionic Character

The percentage ionic character offers a quantitative insight into how much a chemical bond behaves like an ionic bond compared to a purely covalent bond. It takes into account both the observed and theoretical dipole moments of the bond. The formula for calculating percentage ionic character is:\[\text{Percentage Ionic Character} = \left( \frac{\text{Observed Dipole Moment}}{\text{Expected Dipole Moment}} \right) \times 100\]This expression helps establish what fraction of the bond's nature can be attributed to ionic characteristics.

In our example with HCl:

• The observed dipole moment is given as 1.03 D.
• The expected dipole moment, if HCl were completely ionic, is 6.12 D.
• Using the values in the formula results in a percentage ionic character of approximately 16.83%. Thus, HCl is not fully ionic, and it shows partial covalent properties.

This calculation is crucial for understanding the nature of different chemical bonds and predicting the molecule's properties and reactions.

Characteristics of Polar Molecules

Polar molecules are those that possess a net dipole moment because of the unequal sharing of electrons between their constituent atoms. This imbalance in electron sharing results in regions of partial positive and negative charges within the molecule.

Here are some key characteristics of polar molecules:

• They have a significant dipole moment as a result of distinct electronegativity differences between bonded atoms.
• Polar molecules tend to align in the presence of an electric field and dissolve well in polar solvents such as water due to their ability to form hydrogen bonds and electrostatic interactions.
• In polar molecules like HCl, the molecule has one end that is partial positive, and the other is partial negative, causing strong dipole-dipole interactions.

These properties are essential in numerous chemical processes, affecting how substances mix, react, and contribute to biological function. Understanding polar molecules is a cornerstone of molecular chemistry, helping in the design of new materials and drugs.