The electronegativity calculator above returns the Pauling electronegativity of two elements you select, the difference between them, and the classification that difference conventionally implies: nonpolar covalent, polar covalent or ionic. It also computes the percent ionic character from Pauling's own empirical expression, which gives a continuous measure rather than a category and is usually the more honest way to describe a bond.
Arb Digital publishes free calculators that show the working rather than just the answer. On this topic that matters because the categories are softer than they look. The threshold values differ between textbooks, the percent ionic character varies smoothly with no steps in it, and a great many real bonds sit close enough to a boundary that the label depends on which book you opened.
What This Electronegativity Calculator Does
It holds the Pauling electronegativity values for the main group elements, the transition metals and several actinides, and returns the values for any pair you choose along with the absolute difference. From that difference it derives two things: the conventional bond classification under whichever set of thresholds you select, and the percent ionic character from Pauling's exponential expression. The bar breakdown shows the ionic and covalent shares side by side.
It also names the negative end of the bond, meaning the atom that carries the partial negative charge because it holds the shared electrons more tightly. That direction is what a dipole arrow points at, and it is the piece students most often get backwards.
The custom value fields exist because Pauling's is not the only electronegativity scale. Mulliken defines it from ionisation energy and electron affinity, Allred and Rochow from effective nuclear charge and covalent radius, and Allen from average valence electron energy. The numbers differ, and the orderings differ slightly too. Entering a value manually lets you run the same comparison on a scale other than Pauling's.
How to Use It
- Select both elements from the lists. The order does not matter, since the difference is taken as an absolute value.
- Read the difference from the hero and the classification underneath it.
- Choose a threshold scale if your course or text uses cut-offs other than 0.4 and 1.7.
- Check the percent ionic character in the grid, which is a continuous figure and does not jump at a boundary.
- Enter a custom value for either element if you are working on a scale other than Pauling's.
The Scale and How the Numbers Are Derived
Electronegativity is the tendency of an atom in a molecule to attract shared electrons. Pauling built his scale from bond energies rather than from any single atomic property. He observed that the bond A–B is almost always stronger than the average of A–A and B–B, and attributed the excess to ionic contribution. Defining that excess as Δ in electronvolts, the electronegativity difference is roughly √Δ, and the whole scale is then anchored so that fluorine, the most electronegative element, sits at 3.98.
Because the scale is built from a difference, only differences are strictly meaningful. The absolute numbers are a convenient bookkeeping device, and the scale is dimensionless. Values run from about 0.7 for francium and caesium to 3.98 for fluorine, and this page covers elements 1 to 92 where a Pauling value is conventionally quoted. Helium, neon and argon have none, since they form no ordinary bonds for the derivation to use.
Percent ionic character comes from Pauling's own fit: %IC = 100 × [1 − exp(−0.25 × ΔEN²)]. For sodium chloride, with chlorine at 3.16 and sodium at 0.93, ΔEN is 2.23, so ΔEN² is 4.973, and the expression gives 100 × (1 − e⁻¹·²⁴³) = 71.2 percent. For the O–H bond in water, ΔEN is 1.24 and the figure falls to 31.9 percent. Critically evaluated atomic data for the elements is collected in the NIST periodic table of the elements, and the formal definition of the quantity is given by IUPAC in the IUPAC Gold Book entry for electronegativity.
The Thresholds Are a Convention, Not a Fact
The cut-offs of 0.4 and 1.7 are the most widely taught, and they have no physical basis. The 1.7 figure was chosen because it corresponds to roughly fifty percent ionic character on Pauling's own expression, which is a defensible place to put a line but not a natural boundary in anything. Other texts use 0.5 and 2.0, or 0.4 and 1.8, and all of them are defensible in the same weak sense.
Two well-known cases show why the categories mislead. Hydrogen fluoride has a difference of 1.78, above the common threshold, yet it is a covalent molecular gas with a boiling point of 20 °C, nothing like an ionic compound. Aluminium chloride has a difference of 1.55, below the threshold, yet aluminium chloride is far more ionic in the solid than that suggests and its behaviour changes drastically with phase. Physical state, lattice structure and polarisability all matter, and none appear in the difference.
The practical advice is to quote the percent ionic character rather than the label wherever you can, and to say which threshold scale you used whenever you cannot. A bond described as 71 percent ionic communicates something specific. A bond described as ionic communicates something that depends on the reader's textbook.
Why Electronegativity Follows the Periodic Table
Electronegativity rises across a period and falls down a group, which is the same pattern as ionisation energy and the reverse of atomic radius. All three come from the same cause. Across a period the effective nuclear charge on the valence electrons increases by roughly 0.65 per element while the shell stays the same, so the atom pulls harder on shared electrons. Down a group the valence shell moves further from the nucleus and the added inner shells screen it almost completely, so the pull weakens.
That is why fluorine, at the top right of the reactive elements, is the maximum, and why caesium and francium at the bottom left are the minimum. It is also why the diagonal relationships exist: lithium and magnesium have similar electronegativities, as do beryllium and aluminium, because moving right raises the value while moving down lowers it and the two effects roughly cancel along a diagonal. If you want to see the screening arithmetic that produces this trend, the effective nuclear charge calculator works it out term by term, and the electron configuration calculator gives the filling that underlies it.
The transition metals break the neat pattern. Their electronegativities cluster between about 1.3 and 2.4 and do not vary smoothly, because d electrons screen poorly and the relevant valence shell is not simply the outermost one. Gold at 2.54 is more electronegative than many nonmetals, which is part of why it is so resistant to oxidation.
What the Difference Predicts, and What It Does Not
The difference is a good predictor of bond polarity, which is the separation of charge along a single bond. It tells you which atom carries the partial negative charge and roughly how much. That in turn helps predict where a nucleophile attacks, which bonds are susceptible to hydrolysis, and how solvents interact.
It is not a predictor of molecular polarity, and conflating the two is the most consequential error on this topic. Carbon dioxide has two strongly polar C=O bonds, each with a difference of 0.89, and no molecular dipole whatsoever, because the molecule is linear and the two bond dipoles cancel exactly. Carbon tetrachloride is the same story in three dimensions. Molecular polarity requires the geometry as well as the bond differences, and the geometry comes from the electron pair arrangement, not from this page.
Nor does electronegativity difference predict bond strength, reaction rate or acidity in any direct way. It contributes to all of them and determines none. For the bonding descriptions that go alongside it, see the bond order calculator for the covalent side and the lattice energy calculator for the ionic side, which quantifies how strongly an ionic solid is actually held together.
Using Electronegativity in Practice
Two habits make the concept genuinely useful rather than decorative. The first is to work in differences and never in absolute values. Saying that oxygen is at 3.44 tells you nothing on its own; saying that the O–H difference is 1.24 while the O–C difference is 0.89 tells you immediately why water is a much better hydrogen bond donor than an ether.
The second is to use it for ranking rather than for prediction. Comparing the polarity of a series of C–X bonds as X moves down the halogens gives a reliable ordering and a reliable explanation for a trend in reactivity. Trying to predict an absolute property from a single difference generally does not work. Where you need to identify which species are actually charged in solution, the net ionic equation calculator is the more direct route, and for composition rather than bonding, the percent composition calculator and the molar mass calculator handle the mass side.
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Browse All Free Tools Suggest a ToolCommon Mistakes to Avoid
- Treating bond polarity as molecular polarity — carbon dioxide has two very polar bonds and no net dipole because the geometry cancels them.
- Quoting a category without the threshold — 0.4 and 1.7 is a convention, and other texts use different lines.
- Comparing values across scales — Pauling, Mulliken and Allen values are not interchangeable, and mixing them corrupts the difference.
- Pointing the dipole the wrong way — the more electronegative atom is the negative end, so the arrow points toward it.
- Expecting a Pauling value for helium, neon or argon — the scale is built from bond energies and those elements provide none.
Related Free Tools From Arb Digital
The effective nuclear charge calculator derives the screening that produces the periodic trend, and the electron configuration calculator gives the filling behind it. For bonding itself, use the bond order calculator and the lattice energy calculator. The net ionic equation calculator handles species in solution, and the molar mass calculator and percent composition calculator cover the mass side of a formula. The full free online tools hub lists everything else.
Frequently Asked Questions
It is the tendency of an atom in a molecule to attract the electrons of a shared bond. The Pauling scale is dimensionless and derived from bond energies, running from about 0.7 for caesium to 3.98 for fluorine.
Under the most commonly taught scale, a difference below 0.4 is nonpolar covalent, between 0.4 and 1.7 is polar covalent, and above 1.7 is treated as ionic. These cut-offs are conventions, and other texts place them differently.
A continuous measure from Pauling's empirical expression, 100 times one minus the exponential of minus a quarter of the squared difference. Sodium chloride comes out at about 71 percent, and the O–H bond in water at about 32 percent.
The more electronegative one, because it holds the shared electrons more closely. A dipole arrow is drawn pointing toward that atom, with the crossed tail at the partially positive end.
No. Molecular polarity depends on geometry as well. Carbon dioxide has two strongly polar bonds and no molecular dipole, because the linear shape makes the two bond dipoles cancel exactly.
Because the Pauling scale is derived from bond energies, and those elements do not form the ordinary bonds the derivation needs. Krypton and xenon are quoted because they do form compounds.
No. They are separate scales defined from different measurements, and although they broadly agree on ordering, the numbers differ. A difference is only meaningful when both values come from the same scale.
This calculator is provided for education and general reference. It reports published tabulated values and a published empirical relationship, and it is not laboratory, handling or safety guidance for any element or compound.
