Definition · Plain-language
Electronegativity
Electronegativity is a measure of how strongly an atom attracts the shared electrons in a chemical bond.
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The pull on bonding electrons
When two atoms form a covalent bond, they share a pair of electrons, but they do not necessarily share equally. Electronegativity measures how strongly an atom draws those shared electrons toward itself. An atom with high electronegativity holds the bonding electrons more tightly; one with low electronegativity lets them drift away. The concept is most often quantified on the Pauling scale, a relative scale on which fluorine, the most electronegative element, is assigned the highest value, and other elements are placed in comparison.
The periodic trend
Electronegativity follows a clear pattern across the periodic table. It generally increases from left to right across a period, because the growing nuclear charge pulls electrons in more strongly while the shell stays the same. It generally decreases down a group, because the outer electrons sit further from the nucleus and are shielded by inner shells, weakening the pull. As a result, the most electronegative elements are toward the top right (fluorine, oxygen, nitrogen), and the least electronegative toward the bottom left. The noble gases are usually left out, as they rarely bond.
Electronegativity and bond polarity
The difference in electronegativity between two bonded atoms decides the character of their bond. If the difference is zero or very small, the electrons are shared evenly and the bond is non-polar covalent. A moderate difference gives a polar covalent bond, in which the more electronegative atom carries a slight negative charge and its partner a slight positive charge. A large difference means electrons are effectively transferred, producing an ionic bond. Electronegativity therefore provides a single, continuous way to understand bonding, from purely covalent to purely ionic.
Key facts
At a glance
- Definition: an atom’s tendency to attract shared bonding electrons
- Common scale: the Pauling scale (relative values)
- Most electronegative: fluorine
- Across a period: generally increases (left to right)
- Down a group: generally decreases
- Determines: bond polarity, from non-polar to polar to ionic
Common misconceptions
What people often get wrong
Often heard: Electronegativity is the same as an atom’s overall charge.
Actually: Electronegativity is a tendency to attract shared electrons in a bond, not a charge. A neutral atom still has a definite electronegativity that describes how it behaves when bonded.
Often heard: Electronegativity increases steadily down a group.
Actually: It generally decreases down a group, because the bonding electrons are further from the nucleus and more shielded. It increases across a period from left to right.
Often heard: A bond is either fully covalent or fully ionic, with nothing in between.
Actually: Electronegativity difference gives a continuous range. Small differences give non-polar covalent bonds, moderate ones give polar covalent bonds, and large ones give ionic bonds.
