Electronegativity
Definition and meaning of Electronegativity in chemistry.
Electronegativity is a measure of an atom's ability to attract and hold onto the shared electrons in a chemical bond. Atoms with high electronegativity pull bonding electron density toward themselves more strongly than atoms with low electronegativity.
In more detail
Electronegativity is a relative, dimensionless property most commonly expressed on the Pauling scale, which runs from about 0.7 (cesium) to 3.98 (fluorine). It generally increases left to right across a period, as nuclear charge increases, and decreases down a group, as atomic radius and electron shielding increase. The electronegativity difference between two bonded atoms predicts bond character: a small difference gives a nonpolar covalent bond, a moderate difference gives a polar covalent bond, and a large difference favors an ionic bond.
Key facts
| Field | General Chemistry |
|---|---|
| Common scale | Pauling scale, ~0.7 to 3.98 |
| Most electronegative element | Fluorine (3.98) |
| Periodic trend | Increases across a period, decreases down a group |
In hydrogen fluoride (HF), fluorine (Pauling value 3.98) is far more electronegative than hydrogen (2.20), so the bonding electrons sit closer to fluorine, creating a polar covalent bond with a partial negative charge on F and a partial positive charge on H.
Frequently asked questions
How is electronegativity different from electron affinity?
Electronegativity is a relative tendency of an atom to attract shared electrons within a bond, while electron affinity is the measurable energy change when an isolated gaseous atom gains an electron to form an anion.
How does electronegativity difference predict bond type?
A difference below about 0.5 typically indicates a nonpolar covalent bond, 0.5 to 1.7 indicates a polar covalent bond, and above about 1.7 the bond is usually considered ionic, though these are approximate guidelines, not sharp cutoffs.