Electronegativity Calculator (Pauling values, Δχ and bond type for two elements)

Understanding the electronegativity calculator — concept and principle

This calculator looks up the Pauling electronegativity of two elements, finds their difference Δχ, classifies the bond as nonpolar covalent, polar covalent or mostly ionic, shows which atom carries the partial negative charge, and estimates the percent ionic character. It is a staple of general-chemistry homework on bond polarity.

How it is calculated

Δχ = |χ1 − χ2|

• Below 0.4: nonpolar covalent; 0.4 to 1.8: polar covalent; above 1.8: mostly ionic.
• The more electronegative atom is the partial negative end (δ−).
• Pauling's estimate of ionic character = (1 − e^(−Δχ²/4)) × 100%.
• Values are on the Pauling scale; fluorine is highest at 3.98 and caesium among the lowest at 0.79.

The principle

Electronegativity describes how strongly an atom in a molecule pulls shared electrons towards itself. Pauling derived his scale from bond energies: a bond between unlike atoms is stronger than the average of the two like bonds, and the extra stability grows with the electronegativity difference. When Δχ is small the electrons are shared almost equally; as it grows, the electron pair shifts towards one atom, until at large differences the bond is better described as ions held together by attraction. The cut-offs are conventions, and textbooks put the ionic boundary anywhere from 1.7 to 2.0.

Worked example

Default inputs: hydrogen (2.20) and chlorine (3.16).

1. Δχ = |2.20 − 3.16| = 0.96.
2. 0.96 lies between 0.4 and 1.8, so the bond is polar covalent.
3. Chlorine is more electronegative, so Cl is the δ− end.
4. Ionic character = (1 − e^(−0.96²/4)) × 100 = (1 − e^(−0.2304)) × 100 = 20.6%.

How to read the result

Treat bond type as a spectrum rather than three boxes. A Δχ of 0.96 means a clearly polar bond with a dipole moment, which is why HCl dissolves well in water. Δχ above 2, as in NaCl or KF, points to ionic compounds. Bonds between two metals are metallic whatever Δχ says.

Common mistakes

• Treating the cut-offs as sharp physical limits.
• Applying the rule to metal–metal pairs.
• Concluding that a molecule is polar from polar bonds alone. Symmetric molecules such as CO₂ have polar bonds but no net dipole.
• Mixing Pauling values with Mulliken or Allen scales.

Frequently asked questions

Which element is the most electronegative?

Fluorine, at 3.98 on the Pauling scale.

Is a C–H bond polar?

With χ = 2.55 and 2.20, Δχ is 0.35, so it is usually classed as nonpolar.

Why are noble gases missing?

Most of them form no bonds that would give a Pauling value.

Sources: L. Pauling, The Nature of the Chemical Bond, 3rd ed. (Cornell University Press, 1960)