Bond Polarity and Dipole Moments Explained, with a Free Checker

Bond polarity and electronegativity

Electronegativity (χ) is the pull an atom has on the electrons in a bond. On the Pauling scale fluorine is highest at 3.98, then oxygen 3.44, chlorine 3.16 and nitrogen 3.04. Carbon is 2.55 and hydrogen 2.20.

In a bond between two different atoms the electrons spend more time near the more electronegative atom. It gains a partial negative charge (δ−) and the other atom a partial positive charge (δ+). This charge separation is a bond dipole.

Percent ionic character can be estimated with Pauling’s formula: % ionic = (1 − e^(−ΔEN²/4)) × 100. A ΔEN of 1.7 gives about 51% ionic, which is where the 1.7 cut-off comes from.

When is a molecule polar?

Bond dipoles are vectors. Add them using the 3D shape of the molecule:

1. Draw the Lewis structure and find the shape with VSEPR.
2. Draw a dipole arrow on every polar bond, pointing to the δ− atom.
3. Add the arrows. If they cancel, the molecule is nonpolar. If not, it is polar.

A simple test: a molecule is nonpolar when the central atom has no lone pairs and all outer atoms are identical (CO₂, BF₃, CCl₄, PCl₅, SF₆). Two shapes with lone pairs are still symmetric and nonpolar: linear AX₂E₃ (XeF₂) and square planar AX₄E₂ (XeF₄). Lone pairs in other shapes (NH₃, H₂O, SF₄, ClF₃) or different outer atoms (CHCl₃, CH₂Cl₂) give a net dipole.

How to use the bond polarity and dipole checker

1. Open the bond polarity and dipole checker.
2. In Bond: two elements, choose Element A and Element B, or press an example such as H–Cl, C–O or Na–Cl. The result shows ΔEN, the bond type on a colour scale, which atom is δ− and the % ionic character with the working. Swap A and B reverses the pair.
3. Switch to Molecule: polar or nonpolar?. Type a formula such as XeF4 or a SMILES string such as Cl/C=C\Cl and press Check polarity, or press an example.
4. Read the shape, electron geometry, bond angle, the vector sum of the bond dipoles and, where known, the measured dipole moment in debye.
5. The drawing shows δ+ and δ− on each atom, a purple arrow on each polar bond and a teal net dipole arrow when the molecule is polar. Dashed bonds point away from you.
6. The Reasoning list explains each step, so you can copy the logic into an answer.

Worked examples

1. H–Cl bond

ΔEN = 3.16 − 2.20 = 0.96, so the bond is polar covalent with Cl δ− and H δ+. % ionic = (1 − e^(−0.2304)) × 100 = 20.6%. HCl has a dipole moment of 1.11 D.

2. Water, H₂O

O has 2 bonded atoms and 2 lone pairs: AX₂E₂, bent, 104.5°. Each O–H bond has ΔEN = 1.24 with O δ−. The two dipoles point partly the same way, so they add up. Water is polar, 1.85 D.

3. CCl₄ and CHCl₃

Both are tetrahedral. In CCl₄ the four C–Cl dipoles (ΔEN 0.61) cancel: nonpolar, 0 D. In CHCl₃ one Cl is replaced by H, so the dipoles no longer cancel: polar, 1.04 D.

4. SF₄ and XeF₄

SF₄ is AX₄E, seesaw shaped: the S–F dipoles do not cancel, so it is polar (0.63 D). XeF₄ is AX₄E₂, square planar with the two lone pairs opposite each other: the Xe–F dipoles cancel, so it is nonpolar.

5. cis- and trans-1,2-dichloroethene

Both are flat. In the cis isomer both C–Cl dipoles point to the same side: polar, 1.90 D. In the trans isomer they point in opposite directions and cancel: nonpolar, 0 D. This difference is why the cis isomer boils higher (60 °C) than the trans isomer (48 °C).

Summary table

Common mistakes

• Assuming polar bonds always give a polar molecule. Symmetry can cancel them.
• Judging the shape from a flat drawing. CH₂Cl₂ drawn as a flat cross looks symmetric, but it is tetrahedral and polar.
• Forgetting the lone pairs on the central atom, which change the shape.
• Pointing the dipole arrow toward the δ+ atom.
• Treating 0.4 and 1.7 as sharp borders. Bond character changes smoothly with ΔEN.
• Calling every compound with ΔEN above 1.7 ionic. H–F is a covalent molecule; bonds between two non-metals stay covalent.

Exam tips (JEE, NEET, AP, A-level)

• Always state the shape first, then whether the dipoles cancel.
• JEE and NEET often ask for the order of dipole moments, for example NH₃ (1.47 D) > NF₃ (0.24 D): in NH₃ the lone pair and the bond dipoles point the same way, in NF₃ they oppose.
• AP Chemistry links polarity to intermolecular forces: polar molecules have dipole–dipole forces and usually higher boiling points.
• A-level answers on cis/trans isomers should mention that the trans isomer is nonpolar because the C–Cl dipoles cancel.
• Quote ΔEN to two decimal places with the Pauling values given in your data booklet.

Related tools

Related guides