A dipole moment is a measure of the separation of positive and negative charges in a molecule. It tells us how polar a molecule is.
Key Points:
- A dipole forms when two atoms in a bond have different electronegativities, so electrons are shared unequally.
- The more electronegative atom pulls the shared electrons closer, becoming slightly negative (δ–), while the other atom becomes slightly positive (δ+).
- The dipole moment (μ) is defined as the product of the magnitude of charge (q) and the distance (d) between the charges: μ=q×d
- It is a vector quantity, having both magnitude and direction (from positive to negative).
Units:
- Measured in Debye (D), where
1 D ≈ 3.34 × 10⁻³⁰ C·m.
Examples:
- HCl molecule: Hydrogen (δ+) and Chlorine (δ–) create a strong dipole moment.
- CO₂ molecule: Each C=O bond has a dipole, but they cancel out because the molecule is linear → net dipole moment is zero (nonpolar).
- H₂O molecule: The bent shape means dipoles don’t cancel → strong net dipole moment.