Covalent radius

Covalent radius is half the internuclear distance between two identical atoms joined by a covalent bond. It is an effective, bond-dependent measure of atomic size rather than a sharp physical boundary.

Covalent bond: A chemical bond formed when atoms share one or more pairs of electrons. The radius is inferred from the internuclear distance in this kind of bond.
X-ray crystallography: A method that infers atomic structures from the diffraction of X-rays by crystals. It provides precise internuclear distances used to estimate covalent radii.
Metallic radius: Half the distance between neighboring nuclei in a metallic crystal. It describes metal coordination rather than the distance in a covalent bond.
Bond valence method: A method for assessing chemical bonding in crystals from measured bond lengths and empirical bond-valence parameters. Related distance-based parameters use bond lengths to characterize bonding in solids.
Bond length: The distance between the nuclei of two bonded atoms at their equilibrium geometry. For identical bonded atoms, covalent radius is defined as half this distance.
Gas electron diffraction: A structural method that derives molecular geometry from electron scattering by gas-phase molecules. It measures bond lengths without relying on a crystal lattice.
Van der Waals radius: Half the separation between nonbonded atoms at their closest typical approach. It concerns nonbonded contacts and is generally larger than a covalent radius.
Molecular geometry: The three-dimensional arrangement of atoms in a molecule. Covalent radii offer rough distance estimates when constructing molecular structures.
Atomic radius: A measure of an atom's size, defined differently according to the interaction or boundary being considered. Covalent radius is one operational definition within this broader family of size measures.
Homonuclear molecule: A molecule composed of atoms of a single chemical element. Its identical bonded atoms make each covalent radius half the measured bond length.

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