Which of the following best describes the polarity for acetone?
A. Acetone has polar bonds but is a nonpolar molecule.
B. Acetone has nonpolar bonds and is also a nonpolar molecule.
C. Acetone has polar bonds and is also a polar molecule.
D. Acetone has nonpolar bonds but is a polar molecule.
The Correct Answer and Explanation is :
The correct answer is C. Acetone has polar bonds and is also a polar molecule.
Explanation:
Acetone (CH₃COCH₃) is a small organic molecule that is often used as a solvent. To understand its polarity, we need to examine both the polarity of the individual bonds and the overall structure of the molecule.
- Polar Bonds:
Acetone contains a carbonyl group (C=O), where carbon is covalently bonded to oxygen. Oxygen is more electronegative than carbon, so it pulls electron density away from the carbon, resulting in a polar bond between carbon and oxygen. The oxygen atom carries a partial negative charge (δ-), while the carbon atom carries a partial positive charge (δ+). The C-H bonds in the methyl groups (CH₃) are relatively nonpolar since the electronegativity difference between carbon and hydrogen is small, but they do not significantly cancel the polarity of the carbonyl group. - Molecular Shape and Dipole Moment:
The overall molecular structure of acetone is bent around the central carbonyl group, which creates a separation of charges across the molecule. The C=O bond contributes to a dipole, and the two CH₃ groups do not symmetrically cancel this dipole. As a result, acetone as a whole has a net dipole moment, making it a polar molecule. - Polarity of the Molecule:
Because of the polarity of the C=O bond and the asymmetrical distribution of atoms around the molecule, acetone behaves as a polar molecule. The presence of the polar bond and the lack of symmetry lead to an overall dipole moment, meaning acetone is polar.
Thus, the key points are that acetone has polar bonds (especially the C=O bond), and due to the molecule’s shape and distribution of electrons, it is classified as a polar molecule.