Electronegativity
Electronegativity is a measure of the tendency of an atom to attract a shared pair of electrons toward itself within a covalent bond, expressed on a dimensionless scale. The most widely used scale is the Pauling scale, where fluorine is assigned the highest value of 3.98, making it the most electronegative element, and caesium the lowest at 0.79. Electronegativity determines bond polarity, the character of chemical bonds (ionic vs. covalent), and influences molecular properties such as reactivity, acid strength, and solubility.
Key Formula
E_A - E_B = 0.102 × √(|Δχ_AB|)
LaTeX: E_A - E_B = 0.102\sqrt{|\Delta\chi_{AB}|}
| Symbol | Meaning | Unit |
|---|---|---|
| E_A, E_B | Bond dissociation energies of A-A and B-B homonuclear bonds | eV |
| Δχ_AB | Electronegativity difference between A and B | Pauling units |
Worked Example
Problem
Place the following bonds in order of increasing polarity using Pauling electronegativities: C–H (χ_C = 2.55, χ_H = 2.20), O–H (χ_O = 3.44, χ_H = 2.20), N–H (χ_N = 3.04, χ_H = 2.20), F–H (χ_F = 3.98, χ_H = 2.20).
Solution
Step 1: Calculate Δχ for each bond: C–H: |2.55 − 2.20| = 0.35 N–H: |3.04 − 2.20| = 0.84 O–H: |3.44 − 2.20| = 1.24 F–H: |3.98 − 2.20| = 1.78 Step 2: Rank from smallest to largest Δχ (least polar to most polar). Step 3: C–H (0.35) < N–H (0.84) < O–H (1.24) < F–H (1.78).
Answer
Order of increasing polarity: C–H < N–H < O–H < F–H.
Pauling Electronegativity Values of Common Elements
| Element | Symbol | Electronegativity (Pauling) | Period | Group |
|---|---|---|---|---|
| Fluorine | F | 3.98 | 2 | 17 |
| Oxygen | O | 3.44 | 2 | 16 |
| Nitrogen | N | 3.04 | 2 | 15 |
| Chlorine | Cl | 3.16 | 3 | 17 |
| Carbon | C | 2.55 | 2 | 14 |
| Hydrogen | H | 2.20 | 1 | 1 |
Interactive Tools
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Related Terms
Polar Covalent Bond
A polar covalent bond is a covalent bond in which the electrons are shared unequally between two atoms due to a difference in their electronegativities, creating partial positive (δ+) and partial negative (δ−) charges on the atoms. This unequal sharing results in a bond dipole, where one end of the bond has greater electron density than the other. Polar covalent bonds are fundamental to understanding molecular polarity, solubility, and intermolecular forces — for example, the O–H bonds in water make it an excellent polar solvent.
Ionic Bond
An ionic bond is a type of chemical bond formed through the complete transfer of one or more electrons from a metal atom to a non-metal atom, creating oppositely charged ions that attract each other electrostatically. This electrostatic attraction between cations (positively charged) and anions (negatively charged) holds the compound together in a crystal lattice structure. Ionic bonds are responsible for the properties of salts such as high melting points, brittleness, and electrical conductivity when dissolved in water.
Covalent Bond
A covalent bond is a type of chemical bond formed when two atoms share one or more pairs of electrons, resulting in a stable arrangement for both atoms. This sharing occurs most commonly between non-metal atoms that have similar electronegativities, allowing each atom to achieve a full valence shell without complete electron transfer. Covalent bonds are the foundation of organic chemistry and molecular biology, governing the structure of molecules ranging from water (H₂O) to complex proteins.
From Greek "elektron" (amber, electricity) and Latin "negativus" (denying). The concept was formally quantified by Linus Pauling in 1932, earning him a share of the basis for his 1954 Nobel Prize in Chemistry.