elektronegativity

Elektronegativity, often spelled electronegativity, is the tendency of an atom to attract electrons in a chemical bond. It is a dimensionless quantity used to describe bond polarity. No single physical unit defines electronegativity; instead scales correlate experimental observables. The most common scales are Pauling, Mulliken, and Allred–Rochow. The Pauling scale assigns values by comparing bond dissociation energies; Mulliken defines it as half the sum of the ionization energy and electron affinity (scaled). Allred–Rochow uses effective nuclear charge divided by covalent radius.

Periodic trends: Across a period, electronegativity increases from left to right, due to increasing nuclear charge and similar shielding. Down a group, it decreases with increasing atomic size and shielding. Fluorine is the most electronegative element; cesium and francium are among the least. The trend can vary in different bonding environments and oxidation states.

Bond polarity: The difference in electronegativity between two bonded atoms determines bond character. Large differences yield ionic bonds; moderate differences yield polar covalent bonds; small differences yield nonpolar covalent bonds. This polarity influences dipole moments, reactivity, acidity of conjugate bases, and molecular geometry.

Notes: Electronegativities are context-dependent and approximate; they are useful heuristics for predicting molecular structure and behavior rather than exact intrinsic properties. They underpin explanations of acid-base strength, catalysis, and material properties.