Electronegativity: definition in chemistry
Electronegativity: How strongly an atom attracts the shared electrons in a chemical bond. Fluorine is the most electronegative element.
Electronegativity is usually given on the Pauling scale, which runs from about 0.8 for cesium to 3.98 for fluorine. The difference in electronegativity between two bonded atoms predicts the type of bond: a small difference gives a nonpolar covalent bond, a moderate one a polar covalent bond, and a large one (roughly above 1.7 to 2.0) an ionic bond.
Examples
- Fluorine — 3.98, the highest of all elements
- Oxygen — 3.44, which makes the O–H bonds in water polar
- Sodium (0.93) and chlorine (3.16) differ by 2.23, so NaCl is ionic
- Carbon (2.55) and hydrogen (2.20) are close, so C–H bonds are nearly nonpolar
On the periodic table
Electronegativity increases from left to right across a period and decreases down a group, so the highest values are at the top right (excluding the noble gases) and the lowest at the bottom left.