1.441
Debye
1.441
Debye
4.806530e-30
C·m
30
%
1
1.441
Debye
1.441
Debye
4.806530e-30
C·m
30
%
1
The Dipole Moment Calculator computes the electric dipole moment of a polar bond or molecule from the magnitude of the partial charges and the separation between them. The electric dipole moment is a fundamental property describing the polarity of a molecule — how asymmetrically the electron density is distributed.
A dipole moment arises whenever there is a separation between centers of positive and negative charge. For a diatomic molecule, mu = q * d, where q is the magnitude of the partial charge and d is the bond length. For polyatomic molecules, the total dipole moment is the vector sum of all bond dipoles, which is why CO2 (linear, symmetric) has zero net dipole moment despite having polar C=O bonds, while H2O (bent, 104.5 degree angle) has a large net dipole moment of 1.85 Debye.
The Debye unit (1 D = 3.336 x 10^-30 C·m) is the standard unit for molecular dipole moments. Water has mu = 1.85 D, HCl = 1.08 D, HF = 1.82 D, NH3 = 1.47 D, CO = 0.11 D. The dipole moment determines polarity, solubility (like dissolves like), boiling point (stronger dipole-dipole interactions mean higher boiling point), and molecular recognition.
Percent ionic character can be estimated from the ratio of the actual dipole moment to the value expected for a fully ionic bond (mu_ionic = e * d). For HCl, the actual dipole moment is about 18% of the fully ionic value, indicating significant covalent character.
Dipole moments are measured experimentally by microwave spectroscopy (pure rotational spectra depend on the dipole moment) and by measuring the dielectric constant of the substance as a function of temperature (Debye equation).
Single bond dipole: mu = q * d, where q = partial_charge * e = charge_e * 1.602e-19 C, d = bond length in meters. In Debye: mu_D = mu_Cm / 3.336e-30. For two equal bonds at angle theta to each other: mu_total = 2 * mu_bond * cos(theta/2). Percent ionic character = |charge_e| * 100%.
mu > 1.5 D indicates a significantly polar bond. mu = 0 means nonpolar. The vector sum for two bonds depends critically on bond angle: for water (104.5 degrees, 2 O-H bonds), the net dipole is large; for CO2 (180 degrees, 2 C=O bonds), the net dipole cancels to zero. Larger percent ionic character means more electron transfer between atoms.
Inputs
Results
Each O-H bond in water has a dipole of ~1.52 D. The vector sum of two O-H bonds at 104.5 degrees gives 1.85 D total, matching the known water dipole moment.
Inputs
Results
HCl has a bond dipole of 1.08 D with ~18% ionic character. The fully ionic H+Cl- pair at 127 pm would give 6.09 D, confirming HCl is largely covalent.
A measure of the polarity of a molecule — the product of charge magnitude and separation between positive and negative charge centers. It is a vector pointing from negative to positive charge (by physics convention) or positive to negative (by chemistry convention).
1 Debye = 3.336 x 10^-30 C·m. It corresponds to the dipole moment of two charges of magnitude 1 atomic charge unit separated by 0.208 angstroms. Most molecular dipoles range from 0 to 5 D.
CO2 is linear (O=C=O, 180 degrees). The two C=O bond dipoles point in exactly opposite directions and cancel, giving zero net dipole moment. The same applies to BF3 (trigonal planar) and CCl4 (tetrahedral).
Polar molecules have stronger intermolecular dipole-dipole interactions, requiring more energy to separate. This raises the boiling point. HF (1.82 D) has an anomalously high bp for its size due to both dipole-dipole and hydrogen bonding.
The fraction of a bond's character that is ionic versus covalent. It is estimated as (actual dipole moment) / (fully ionic dipole moment) x 100. HF is about 41% ionic, HCl about 17%, HI about 4%.
Two main methods: (1) Microwave rotational spectroscopy — rotational transitions depend on the dipole moment. (2) Dielectric constant measurements — the Debye equation relates the temperature dependence of molar polarization to the permanent dipole moment.
When the dipole moment is zero by symmetry but charge distribution is nonuniform, the next term in the multipole expansion is the quadrupole moment. CO2 has a significant quadrupole moment, which governs its interactions with other molecules and surfaces.
Polar molecules dissolve well in polar solvents (water, ethanol) due to favorable dipole-dipole interactions. Nonpolar molecules dissolve in nonpolar solvents (hexane, CCl4). This is the basis of the like-dissolves-like rule.
The transition dipole moment describes the interaction of a molecule with electromagnetic radiation during an electronic or vibrational transition. A transition is IR-active only if it involves a change in dipole moment; it is Raman-active if it involves a change in polarizability.
Free atoms are spherically symmetric and have zero permanent dipole moment. However, in the presence of external fields (or neighboring charges) atoms develop induced dipole moments described by their polarizability.
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