Dipole Moment Calculator
Calculate the electric dipole moment from charge separation distance.
Convert between Debye and SI units.
Understand polarity and molecular geometry effects.
The electric dipole moment (μ) measures the separation of positive and negative charge in a molecule. It determines polarity, intermolecular forces, and many physical properties.
Formula:
μ = q × d
Where:
- μ = dipole moment (Debye or C·m)
- q = magnitude of partial charges (in units of electron charge e)
- d = distance between charge centers (pm or Å)
Unit conversion: 1 Debye (D) = 3.336 × 10⁻³⁰ C·m
For bond dipoles, a useful working formula:
μ (Debye) = 4.803 × q_fraction × d (Å)
Where q_fraction is the fractional charge (0 to 1, from electronegativity difference).
Common molecular dipole moments:
| Molecule | μ (D) | Notes |
|---|---|---|
| H₂O | 1.85 | Bent geometry, strong dipole |
| NH₃ | 1.47 | Trigonal pyramidal |
| HF | 1.91 | Highest bond dipole |
| HCl | 1.08 | Moderate |
| CO | 0.11 | Small, C⁻ end is negative |
| CO₂ | 0 | Linear, dipoles cancel |
| CCl₄ | 0 | Tetrahedral, dipoles cancel |
| CHCl₃ | 1.04 | Asymmetric |
| Benzene | 0 | High symmetry |
| Acetone | 2.88 | Large due to C=O |
Vector addition for molecular dipoles: If a molecule has multiple bond dipoles, the net molecular dipole is the vector sum. Symmetric molecules (linear, trigonal planar, tetrahedral with identical substituents) have μ = 0 even though each bond is polar.
μ_net = √(Σμᵢ²) for perpendicular bonds
μ_net = |μ₁ + μ₂ + 2μ₁μ₂cos(θ)| for bonds at angle θ
Effects of dipole moment:
- Boiling point: Higher μ → stronger dipole-dipole forces → higher bp
- Solubility: “Like dissolves like” — polar solvents dissolve polar solutes
- Dielectric constant: High-μ solvents have large dielectric constants (water: 78.4)
- Microwave absorption: Polar molecules absorb microwave radiation (basis of microwave cooking)
Debye unit origin: Named after Peter Debye (1884–1966), Dutch-American physicist. 1 D is approximately the dipole moment of a pair of charges ±0.2e separated by 1 Å.