covalent radius
Sign in to savemeasure of the size of an atom that forms part of one covalent bond
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A covalent radius is a measurement of how large an atom is, specifically based on the distance it takes up when it's bonded to another atom through a covalent bond (where atoms share electrons). This measurement matters because it helps chemists predict how atoms will bond together and what the distances between atoms will be in molecules.
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The covalent radius, rcov, is a measure of the size of an atom that forms part of one covalent bond. It is usually measured either in picometres (pm) or angstroms (Å), with 1 Å = 100 pm.
In principle, the sum of the two covalent radii should equal the covalent bond length between two atoms, R(AB) = r(A) + r(B). Moreover, different radii can be introduced for single, double and triple bonds (r1, r2 and r3 below), in a purely operational sense. These relationships are certainly not exact because the size of an atom is not constant but depends on its chemical environment. For heteroatomic A–B bonds, ionic terms may enter. Often the polar covalent bonds are shorter than would be expected based on the sum of covalent radii. Tabulated values of covalent radii are either average or idealized values, which nevertheless show a certain transferability between different situations, which makes them useful.