Bondlength

Bond length is the equilibrium distance between the nuclei of two bonded atoms in a molecule or ion. It is the most probable internuclear separation of a chemical bond in its ground state and is commonly expressed in picometers or angstroms. Bond length reflects the balance of attractive and repulsive forces as electrons occupy bonding and anti-bonding orbitals.

Bond length is influenced by bond order: higher bond order typically yields shorter bonds (single > double > triple). It also depends on the sizes of the bonded atoms (smaller atoms give shorter bonds), along with factors such as hybridization, resonance, polarization, and conjugation. In organometallic and inorganic chemistry, coordination with metals or highly ionic character can modify metal–ligand distances.

In general trends, bond lengths tend to decrease from left to right across a period as atomic radii shrink, and increase down a group as atoms grow larger. The relationship between bond length and bond energy is not strict, but, all else equal, shorter bonds tend to be stronger.

Bond lengths are determined experimentally by techniques such as X-ray crystallography and electron diffraction; in diatomic or gas-phase molecules, rotational or microwave spectroscopy provides precise internuclear distances. In practice, tables of covalent radii or empirical bond-length data are used to estimate lengths in unknown structures.

Examples: H–H about 74 pm; C–C single about 154 pm; C=C about 134 pm; C≡C about 120 pm; O=O about 120 pm.