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Electronegativity

General

Electronegativity (Pauling Scale)

A measure of an atom's ability to attract shared electrons toward itself in a chemical bond, most commonly expressed on the Pauling scale.

Definition

Electronegativity is a measure of how strongly an atom attracts shared electrons toward itself when it forms a chemical bond with another atom. It is not a directly measurable physical quantity like mass or charge, but rather a relative scale — most commonly the Pauling scale — that ranks elements by their pull on bonding electrons, with fluorine at the top with a value of 3.98.

Electronegativity differences between bonded atoms determine the character of the bond itself. When two atoms have very similar electronegativity, they share bonding electrons roughly equally, forming a nonpolar covalent bond. When the difference is moderate, the more electronegative atom pulls electron density toward itself, creating a polar covalent bond with partial charges. When the difference is large, electrons transfer almost completely to the more electronegative atom, forming an ionic bond.

Electronegativity trends follow clear patterns on the periodic table: it generally increases moving left to right across a period, and decreases moving down a group. The Electronegativity Calculator looks up Pauling values for any two elements and calculates their difference to help predict bond type and polarity.

Formula

Electronegativity itself doesn't come from a single calculation formula — Pauling values are tabulated reference numbers for each element. However, bond character is predicted from the electronegativity difference between two bonded atoms:

ΔEN = |EN(Atom A) - EN(Atom B)|

General interpretation guide:

  • ΔEN < 0.4 → nonpolar covalent bond
  • 0.4 ≤ ΔEN ≤ 1.7 → polar covalent bond
  • ΔEN > 1.7 → ionic bond

Worked Example

Consider a bond between hydrogen (EN = 2.20) and chlorine (EN = 3.16), as in hydrogen chloride (HCl).

ΔEN = |2.20 - 3.16| = 0.96

Since 0.96 falls between 0.4 and 1.7, the H-Cl bond is classified as polar covalent, with chlorine pulling bonding electrons toward itself and creating a partial negative charge on chlorine and a partial positive charge on hydrogen. Try other element pairs with the Electronegativity Calculator.

Key Things to Know

  • The Pauling scale is the standard reference: Nearly all textbook and calculator electronegativity values use the Pauling scale, where fluorine sits at the top with 3.98 and francium near the bottom around 0.7.
  • Electronegativity difference predicts bond type: A small difference points to a nonpolar covalent bond, a moderate difference points to a polar covalent bond, and a large difference points to an ionic bond.
  • Periodic trends are predictable: Electronegativity rises across a period due to increasing nuclear charge, and falls down a group due to increasing atomic size and electron shielding.
  • It explains molecular polarity: The distribution of electronegativity differences across a molecule's bonds, combined with molecular shape, determines whether the molecule as a whole is polar.
  • Noble gases are typically excluded: Because noble gases rarely form conventional bonds, they are often left off electronegativity tables or assigned unusually low or undefined values.

Related Calculators

Electronegativity Calculator →Look up Pauling electronegativity for any element (Z=1–86) and calculate the electronegativity difference between two bonded atoms. Includes bond polarity classification.

Frequently Asked Questions

Fluorine is the most electronegative element, with a Pauling scale value of 3.98, meaning it pulls shared bonding electrons toward itself more strongly than any other element. This is why fluorine almost always forms highly polar or ionic bonds with other elements.
A bond is generally considered nonpolar if the electronegativity difference between the two bonded atoms is less than about 0.4, polar covalent if the difference is between 0.4 and 1.7, and ionic if the difference exceeds about 1.7. The Electronegativity Calculator computes this difference automatically once you select the two bonded elements.
Electronegativity generally increases from left to right across a period on the periodic table, because atoms gain more protons pulling on a similar number of electron shells, increasing nuclear attraction for bonding electrons. It generally decreases going down a group, since additional electron shells shield the nucleus and increase atomic radius.
Differences in electronegativity between bonded atoms create partial positive and negative charges within a molecule, which determine whether the molecule is polar overall and influence properties like boiling point, solubility, and reactivity. Water's high boiling point relative to its small size, for instance, is largely explained by the significant electronegativity difference between oxygen and hydrogen.
The most widely used scale is the Pauling scale, developed by Linus Pauling, which assigns fluorine a value of 3.98 as the most electronegative element and ranges down to about 0.7 for cesium and francium, the least electronegative elements. Other scales exist, such as the Mulliken and Allred-Rochow scales, but Pauling values are the standard reference in most chemistry textbooks.