Definition · Plain-language
Covalent bond
A covalent bond is a chemical bond formed when two atoms share one or more pairs of electrons, typically between non-metal atoms.
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Sharing electrons for stability
Atoms are most stable when their outermost electron shell is full. A covalent bond achieves this through sharing: two atoms each contribute electrons to a shared pair that "counts" toward both atoms’ outer shells. Hydrogen, for example, needs two electrons to fill its shell, so two hydrogen atoms share a pair to form H₂. This sharing is the defining feature of covalent bonding and explains why it dominates between non-metals, which would otherwise have to gain several electrons each to reach stability.
Single, double and triple bonds
The number of shared electron pairs sets the bond order. A single bond shares one pair, as in the H–H bond of hydrogen or the O–H bonds in water. A double bond shares two pairs, as in the O=O of oxygen gas or the C=O of carbon dioxide. A triple bond shares three pairs, as in the very strong N≡N bond of nitrogen gas. More shared pairs generally mean a stronger, shorter bond, which is why nitrogen gas is so unreactive — its triple bond is hard to break.
Polar and non-polar covalent bonds
Sharing is not always equal. When both atoms pull on the electrons with the same strength — as in O₂ or H₂ — the bond is non-polar covalent. When one atom is more electronegative, it pulls the shared electrons closer, creating a polar covalent bond with slightly negative and slightly positive ends. The O–H bonds in water are polar, which is why water is such a good solvent. As the electronegativity difference grows very large, the bond stops being covalent at all and becomes ionic.
Key facts
At a glance
- Definition: a bond formed by sharing one or more pairs of electrons
- Forms between: usually two non-metal atoms
- Why: lets each atom complete a stable outer shell
- Bond orders: single (1 pair), double (2 pairs), triple (3 pairs)
- Polarity: non-polar (equal sharing) or polar (unequal sharing)
- Example: H₂, O₂, H₂O, CH₄, N₂
Common misconceptions
What people often get wrong
Often heard: In a covalent bond, electrons are transferred from one atom to the other.
Actually: That describes an ionic bond. In a covalent bond the electrons are shared between the two atoms, not handed over. Transfer of electrons produces ions; sharing produces molecules.
Often heard: All covalent bonds share electrons perfectly equally.
Actually: Only non-polar covalent bonds share evenly. When the atoms differ in electronegativity, the bond is polar — electrons are pulled toward the more electronegative atom, giving partial charges.
Often heard: Covalent compounds always have low melting points.
Actually: Small covalent molecules often do, because the molecules are weakly attracted to each other. But covalent network solids such as diamond have very high melting points because breaking them means breaking strong covalent bonds throughout.
