Electronegativity Calculator
Select two elements to instantly see their electronegativity values, the difference between them, the resulting bond type (nonpolar covalent, polar covalent, or ionic), and the estimated percent ionic character. Switch between the Pauling and Allred-Rochow scales, or enter custom values to explore any pair. The step-by-step panel shows the full working so you can follow the chemistry.
Formula
Worked example
For NaCl: chi(Na) = 0.93, chi(Cl) = 3.16. Delta-chi = |0.93 - 3.16| = 2.23, which exceeds 1.7, so the bond is Ionic. Percent ionic character = (1 - e^(-0.25 x 2.23^2)) x 100 = (1 - e^(-1.243)) x 100 = (1 - 0.289) x 100 = 71.1%.
What is electronegativity?
Electronegativity is a dimensionless quantity that describes how strongly an atom in a chemical bond attracts the shared pair of electrons toward itself. First quantified systematically by Linus Pauling in the 1930s, it underpins a huge amount of chemistry: bond polarity, acid strength, oxidation states, and the direction of many reactions all trace back to differences in electronegativity between bonded atoms. The most electronegative element is fluorine (chi = 3.98 on the Pauling scale), the least is cesium (chi = 0.79). Values are dimensionless numbers with no official unit.
How to use this calculator
Choose the electronegativity scale (Pauling for most general chemistry work, Allred-Rochow for inorganic applications). Then pick Element A and Element B from the drop-down lists. The calculator instantly looks up both chi values, computes the absolute difference (delta-chi), classifies the bond, and estimates the percent ionic character from the Hanney-Smith formula. Enable "Override with custom values" if you want to enter chi values manually, for example when working with a less common scale or a specific textbook value. The gauge shows where your delta-chi falls in the three bond-type regions, and the chart shows how ionic character rises across the full delta-chi range so you can see the curve shape in context.
Bond type classification and the Pauling scale thresholds
The three bond-type zones come from Pauling-scale convention: delta-chi below 0.4 is nonpolar covalent (the electron cloud is nearly symmetrical), delta-chi from 0.4 to 1.7 is polar covalent (one atom pulls harder, creating a partial positive and partial negative end, a bond dipole), and delta-chi of 1.7 or above is ionic (electron transfer is energetically favourable and the compound forms oppositely charged ions). These thresholds are approximations: real bonds exist on a continuum. A bond with delta-chi of 1.7 is roughly 50% ionic in character; NaF, with delta-chi near 3.0, is about 91% ionic. Covalent bonds in organic molecules such as C-H (delta-chi = 0.35) or C-C (delta-chi = 0) are genuinely nonpolar.
The Hanney-Smith percent ionic character formula
The percent ionic character formula - % ionic = (1 - e^(-0.25 x delta-chi^2)) x 100 - was derived empirically by fitting to measured electric dipole moments divided by the theoretical maximum (if the bond were 100% ionic). It gives a smooth, physically motivated curve: at delta-chi = 0 the character is 0%, at delta-chi = 1.7 it is about 49%, and at delta-chi = 3.3 (as in CsF) it reaches around 93%. The exponential form correctly captures the accelerating shift from covalent to ionic behaviour as the difference grows.
Pauling vs. Allred-Rochow: which scale should I use?
The Pauling scale was established from thermochemical data (bond dissociation energies). It is the default in virtually all introductory chemistry courses and textbooks. The Allred-Rochow scale uses a different physical basis, calculating electronegativity from the effective nuclear charge experienced by a valence electron divided by the square of the covalent radius. It tends to give higher values for nonmetals and some noble gases. For most bond-type and polarity questions the two scales give very similar answers, but they can diverge for transition metals and heavy p-block elements. If your textbook does not specify, use the Pauling scale.
Pauling electronegativity values for common elements
| Element | Symbol | Pauling chi | Allred-Rochow chi |
|---|---|---|---|
| Fluorine | F | 3.98 | 4.1 |
| Oxygen | O | 3.44 | 3.5 |
| Nitrogen | N | 3.04 | 3.07 |
| Chlorine | Cl | 3.16 | 2.83 |
| Bromine | Br | 2.96 | 2.74 |
| Carbon | C | 2.55 | 2.5 |
| Sulfur | S | 2.58 | 2.44 |
| Iodine | I | 2.66 | 2.21 |
| Hydrogen | H | 2.2 | 2.2 |
| Phosphorus | P | 2.19 | 2.06 |
| Silicon | Si | 1.9 | 1.74 |
| Aluminum | Al | 1.61 | 1.47 |
| Iron | Fe | 1.83 | 1.64 |
| Sodium | Na | 0.93 | 1.01 |
| Potassium | K | 0.82 | 0.91 |
| Calcium | Ca | 1 | 1.04 |
| Cesium | Cs | 0.79 | 0.86 |
Values from Pauling (1960). Noble gases with no stable compounds are listed as 0 (no meaningful bond electronegativity).
Frequently asked questions
What does a high electronegativity difference mean for a bond?
A large delta-chi means one atom pulls the shared electrons much more strongly than the other. When delta-chi is below 0.4, electrons are shared roughly equally and the bond is nonpolar covalent. From 0.4 to 1.7 the bond is polar covalent, with a partial negative charge on the more electronegative atom and a partial positive charge on the other. Above 1.7, the attraction is strong enough that electron transfer effectively occurs and the bond is classified as ionic.
Which element has the highest electronegativity?
Fluorine has the highest electronegativity of any element: 3.98 on the Pauling scale and 4.10 on the Allred-Rochow scale. This is why fluorine forms the most polar bonds and the strongest acids in the hydrogen halide series. Cesium and francium have the lowest values (around 0.79 and 0.70 respectively), which is why they react vigorously with electronegative elements to form highly ionic salts.
Can two of the same element form a bond with this calculator?
Yes. If you pick the same element for both A and B (for example H and H), the electronegativity difference is exactly zero, the bond is perfectly nonpolar covalent, and the percent ionic character is 0%. This is the case for all homodiatomic molecules like H2, O2, N2, F2, Cl2, Br2, and I2.
Why does the percent ionic character not reach 100%?
Even the most ionic-seeming bonds retain some covalent character because electron wavefunctions overlap. The Hanney-Smith exponential formula gives about 91% for CsF (delta-chi near 3.2) and about 93% for the most extreme pairs. A true 100% ionic bond would require zero orbital overlap, which does not occur for real chemical bonds. In practice, any bond with percent ionic character above about 50% behaves experimentally as ionic.
Is NaCl ionic or covalent?
NaCl has a Pauling electronegativity difference of |0.93 - 3.16| = 2.23, well above the 1.7 threshold, so it is classified as ionic. The estimated percent ionic character is about 71%. In the solid state NaCl forms a crystal lattice of Na+ and Cl- ions rather than discrete molecules, which is the hallmark of an ionic compound. The bond does retain some covalent character (roughly 29%), but ionic properties dominate.
What is the difference between bond polarity and molecular polarity?
Bond polarity comes from electronegativity differences between two bonded atoms, which this calculator measures. Molecular polarity depends on both the bond polarities and the geometry of the whole molecule. A molecule can have polar bonds but be overall nonpolar if the bond dipoles cancel by symmetry. Carbon dioxide (O=C=O) has two polar C=O bonds (delta-chi = 0.89) but they point in opposite directions and cancel, so CO2 is a nonpolar molecule. Water has two polar O-H bonds and a bent geometry, so the dipoles do not cancel and the molecule is polar.