Question

Which of the following is incorrect? (1) The unit of dipole moment is Debyc, i.c., \(10^{-18}\) esu \(\mathrm{cm}\). (2) Dipole moment is a vector quantity. (3) Decrease in bond angle of triatomic polar molccule decreascs the dipole momcnt. (4) Dipole moment can be used to calculate the magnitude of charge on an atom in a polar molecule.

Short answer

All statements are correct; the question might be flawed.

Step-by-step solution

Understand the unit of Dipole Moment

The dipole moment is measured in Debye, which is correctly represented as \(1 Debye = 10^{-18}\) esu \( \text{cm} \). Therefore, option (1) is correct in stating the unit of dipole moment.

Determine if Dipole Moment is a Vector Quantity

The dipole moment is indeed a vector quantity as it has both magnitude and direction. Hence, option (2) is correct.

Analyze the Impact of Bond Angle on Dipole Moment

In a triatomic polar molecule, an increase or decrease in the bond angle affects the overall dipole moment. As the bond angle decreases, the individual bond dipoles may add up less effectively, possibly decreasing the overall dipole moment. So, option (3) is correct.

Use of Dipole Moment to Calculate Magnitude of Charge

The dipole moment can be used to measure the separation of charge and the magnitude of charge on polar molecules. Therefore, option (4) is also correct.

Conclusion

Since all given options are correct, the question asking for the incorrect statement may contain a typo or error.

Key concepts

Vector Quantity

A dipole moment is an excellent example of a vector quantity. Unlike scalar quantities, which are described only by magnitude, vector quantities also have direction. For instance, when we talk about displacement or velocity, we not only state how much but also in which direction. This is what makes vectors unique.
For dipole moments, the magnitude is given by the product of the charge and the distance between charges, mathematically expressed as:

\( \text{Dipole Moment} = q \times d \)

where \( q \) is the charge and \( d \) is the distance. The direction of the dipole moment points from the negative charge to the positive charge, which tells you how the charges are oriented in space.

When considering multiple dipoles in a molecule, we need to add these dipole moments geometrically, taking both magnitude and direction into account, as we do with any vector addition.

Understanding that dipole moments are vector quantities is essential because it helps us to calculate the net dipole moment in larger, more complex molecules.

Triatomic Polar Molecule

A triatomic polar molecule consists of three atoms, at least one of which is different in electronegativity compared to the others. These differences result in a polar molecule, meaning the molecule has a net dipole moment.

The angle between the atoms, known as the bond angle, plays a significant role in determining the molecule's dipole moment. When this angle changes, it affects how the individual bond dipoles add up.

For example, if the bond angle decreases, the projection of individual dipole moments on the molecular axis may reduce, which can lead to a decreased overall dipole moment. This concept is crucial in understanding the behavior of molecules like water (\(H_2O\)), which is a classic example of a triatomic polar molecule.

Water, with its bent shape and bond angle of about 104.5°, has a significant dipole moment. If this angle were to increase or decrease notably, the dipole moment would also change, altering the molecule's physical and chemical properties.

Charge Magnitude

The magnitude of charge involved in a dipole moment is crucial for understanding various molecular properties. A dipole moment (
\(μ \)) in a molecule is defined as the product of the magnitude of charge (
\(q \)) and the distance (
\(d \)) separating the positive and negative charges, given by the equation:

\( μ = q \times d \)

For polar molecules, knowing the dipole moment allows chemists to calculate the magnitude of the charge on each atom. This information is essential for predicting molecular interactions, solvent behaviors, and reaction mechanisms.

Consider a molecule with a known dipole moment. If we know the distance between charges, we can rearrange our equation to find the charge magnitude:

\( q = \frac{μ}{d} \)

This equation is quite useful in experimental chemistry, as it helps in identifying how strongly atoms within a molecule attract or repel each other, thus influencing the molecule's reactivity and interaction with other substances.