Intermediate Topic 137 of 1102 Bonding & Molecular Structure
Dipole Moment
A measure of charge separation equal to charge times distance, measured in debye.
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In-depth explanation of Dipole Moment
The dipole moment measures the separation of charge in a system and is defined as mu = q times r, with the charge multiplied by the distance between the charges. Its SI unit is the coulomb metre, but the debye is more common, with 1 D equal to 3.34 x 10^-30 C m. The dipole moment is a vector, and the net dipole of a molecule is the vector sum of its bond dipoles. Molecules with a nonzero net dipole are polar, and the dipole moment controls solubility, boiling point and orientation in an electric field. Symmetric molecules can have zero net dipole even when individual bonds are polar.
Going deeper: Dipole Moment
Key ideas: Compute mu equals q times d, with 1 D equal to 3.34 x 10^-30 C m. To estimate percent ionic character, divide the observed value by e times bond length: for HCl, e times 127 pm gives 6.1 D, so 1.08 over 6.1 is about 18 percent. Net dipole of a molecule is the vector sum, so use angles: the water dipole is 2 times the bond dipole times cosine of 52.25 degrees.
Common mistakes and connections: Do not add magnitudes as plain numbers and ignore the angle. Lone pair contributions can partly cancel or add: NH3 is 1.47 D while NF3 is only 0.23 D because lone pair and bond dipoles oppose. Also, a bigger electronegativity difference does not always mean a bigger molecular dipole. Connects to polarity, solubility, dielectric constants and IR activity.
Visualization of Dipole Moment
Measured dipole moments: CO2 is zero because its polar bonds cancel by symmetry, while bent water and pyramidal ammonia have large net dipoles. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Water has a dipole moment of about 1.85 D, whereas carbon dioxide has zero because its two bond dipoles cancel.
Frequently asked questions about Dipole Moment
What is Dipole Moment?
A measure of charge separation equal to charge times distance, measured in debye.
Is Dipole Moment a beginner, intermediate or advanced topic?
Dipole Moment is a intermediate topic in Bonding & Molecular Structure. It builds on the vocabulary of beginner topics in this area.
What should I learn before Dipole Moment?
Study these earlier topics in Bonding & Molecular Structure first: Bond Energy, Bond Order, Bond Polarity.
What comes after Dipole Moment?
The next topics in Bonding & Molecular Structure are Polar and Nonpolar Molecules and Percent Ionic Character.
Can I practise Dipole Moment with quizzes?
Yes. The interactive lesson includes a self-check question on Dipole Moment, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Where Dipole Moment fits in Bonding & Molecular Structure
Dipole Moment is topic 22 of 104 in Bonding & Molecular Structure.