Electronegativity (χ) measures how strongly an atom pulls shared bonding electrons towards itself. Linus Pauling built the most widely used scale from bond energies: fluorine is the most electronegative element at 3.98, oxygen follows at 3.44 and the alkali metals caesium and francium sit at the bottom near 0.7–0.8. Values rise from left to right across a period, because the nuclear charge grows while the shielding barely changes, and fall going down a group, because the valence electrons are farther from the nucleus.
When two atoms bond, the difference between their electronegativities decides how evenly the electrons are shared. Identical atoms (H–H, Cl–Cl) share perfectly; slightly different atoms (C–H, ΔEN = 0.35) are practically nonpolar; a large gap such as O–H (1.24) gives a strongly polar bond with partial charges δ⁺ and δ⁻; and when the gap reaches about 2 – Na–Cl is 2.23 – the electron is effectively transferred and the bond is described as ionic.
Type two element symbols, names or atomic numbers, or switch to custom values if you want to use another scale. The calculator shows both values, the difference, the bond type on a colour scale, the polarity and an estimate of the ionic character.
How to use the Electronegativity Calculator
- Electronegativity values
- First element (symbol, name or atomic number)
- Second element
- Electronegativity of atom A (χ₁)
- Electronegativity of atom B (χ₂)
Everything is calculated in your browser, so results appear instantly and nothing you type is sent to a server.
How it works
The calculator looks up the Pauling electronegativity of each element, takes the absolute difference, classifies the bond with the common 0.4 and 2.0 cut-offs and estimates the ionic character with Pauling’s formula 100 × (1 − e^(−ΔEN²/4)). The more electronegative atom gets the partial negative charge δ⁻.
Worked example
Hydrogen chloride: χ(H) = 2.20 and χ(Cl) = 3.16, so ΔEN = |2.20 − 3.16| = 0.96. That lies between 0.4 and 2.0, so H–Cl is a polar covalent bond, written Hδ⁺–Clδ⁻. Pauling’s formula gives an ionic character of 100 × (1 − e^(−0.96²/4)) ≈ 20.6%.
Sodium chloride: χ(Na) = 0.93 and χ(Cl) = 3.16, so ΔEN = 2.23 – above 2.0, an ionic bond with about 71% ionic character.
Electronegativity differences of common bonds
| Bond | Pauling values | ΔEN | Bond type |
|---|---|---|---|
| C–H | 2.55 / 2.20 | 0.35 | Nonpolar covalent |
| C–O | 2.55 / 3.44 | 0.89 | Polar covalent |
| O–H | 3.44 / 2.20 | 1.24 | Polar covalent |
| N–H | 3.04 / 2.20 | 0.84 | Polar covalent |
| H–F | 2.20 / 3.98 | 1.78 | Polar covalent (very polar) |
| Na–Cl | 0.93 / 3.16 | 2.23 | Ionic |
| K–F | 0.82 / 3.98 | 3.16 | Ionic |
| Cl–Cl | 3.16 / 3.16 | 0 | Nonpolar covalent |
Tips
- Type formulas with normal capitals and numbers, e.g. Ca(OH)2 or CuSO4·5H2O – brackets and hydrates work.
- Atomic masses are IUPAC standard atomic weights; radioactive elements use the mass number of their longest-lived isotope.
- Electronegativity values are on the Pauling scale.
- Everything is calculated in your browser.
Common mistakes to avoid
- Writing CO (carbon monoxide) when you mean Co (cobalt) – capitals matter.
- Forgetting to multiply the bracket contents by the subscript after the bracket.
- Mixing up atomic number (protons) and mass number (protons + neutrons).
Formula
ΔEN = |χ(A) − χ(B)| · ΔEN < 0.4 → nonpolar covalent · 0.4 ≤ ΔEN < 2.0 → polar covalent · ΔEN ≥ 2.0 → ionic · % ionic ≈ 100 × (1 − e^(−ΔEN²/4))Worked example
Inputs — Electronegativity values: Look up two elements (Pauling scale); First element (symbol, name or atomic number): H; Second element: Cl.
Results — Electronegativity difference ΔEN = 0.96; Bond type = Polar covalent bond; Electronegativity of the first atom = 2.2; Electronegativity of the second atom = 3.16; More electronegative atom (gets δ⁻) = Chlorine (Cl); Bond polarity = Hδ⁺ – Clδ⁻.
Key terms
- Electronegativity (χ)
- The tendency of an atom in a molecule to attract the shared bonding electrons towards itself.
- Pauling scale
- Dimensionless electronegativity scale derived from bond dissociation energies, with fluorine at 3.98.
- Polar covalent bond
- A shared electron pair that is pulled towards one atom, giving partial charges δ⁺ and δ⁻.
- Ionic bond
- Electrostatic attraction between ions formed when an electron is effectively transferred from one atom to another.
- Dipole
- A separation of positive and negative charge along a bond or a molecule.
Frequently asked questions
What is the most electronegative element?
Fluorine, with a Pauling electronegativity of 3.98. Oxygen (3.44), chlorine (3.16) and nitrogen (3.04) follow.
What is the least electronegative element?
Caesium (0.79) and francium (about 0.7) have the lowest values; the other alkali metals are all below 1.0.
What electronegativity difference makes a bond ionic?
A difference of about 2.0 or more is usually treated as ionic, 0.4–2.0 as polar covalent and below 0.4 as nonpolar covalent. Some textbooks use 1.7 or 1.8 as the ionic cut-off.
Is the H–Cl bond polar?
Yes. ΔEN = 3.16 − 2.20 = 0.96, so H–Cl is polar covalent with the partial negative charge on chlorine.
Why is the C–H bond considered nonpolar?
Carbon (2.55) and hydrogen (2.20) differ by only 0.35, below the 0.4 cut-off, so the electrons are shared almost evenly. That is why hydrocarbons do not mix with water.
Why do noble gases have no electronegativity value?
Pauling values come from bond energies, and helium, neon and argon form essentially no stable compounds, so no value can be measured. Krypton and xenon, which do form a few compounds, have values of about 3.0 and 2.6.
How does electronegativity change across the periodic table?
It increases from left to right across a period and decreases from top to bottom in a group, so the top-right corner (F, O, Cl, N) holds the highest values.
Is electronegativity the same as electron affinity?
No. Electron affinity is the measured energy change when an isolated gas-phase atom gains an electron; electronegativity describes how strongly an atom attracts shared electrons inside a bond and has no units on the Pauling scale.
What formula does the Electronegativity Calculator use?
ΔEN = |χ(A) − χ(B)| · ΔEN < 0.4 → nonpolar covalent · 0.4 ≤ ΔEN < 2.0 → polar covalent · ΔEN ≥ 2.0 → ionic · % ionic ≈ 100 × (1 − e^(−ΔEN²/4)).