Van der Waals radius

The Van der Waals radius is an atom-specific measure of size, conventionally half the closest distance between two nonbonded atoms of the same element.

Van der Waals interaction: An interaction between atoms or molecules arising from permanent or induced electric multipoles. Nonbonded atoms approach until repulsive interactions balance their attractive van der Waals interactions.
Lennard-Jones potential: A pair potential that models short-range repulsion and longer-range attraction between neutral particles. Its energy minimum and repulsive wall illustrate why nonbonded atoms have a characteristic separation.
van der Waals surface: The molecular boundary formed by spheres centered on atoms with van der Waals radii. Atomic radii combine into a useful approximate surface around a molecule.
Bondi radii: A widely used tabulation of van der Waals radii for chemical elements published by A. Bondi in 1964. Bondi's values are a familiar reference set for assigning nonbonded atomic sizes.
Covalent radius: Half the distance between two identical atoms joined by a covalent bond. It estimates bonded atomic size, unlike the nonbonded separation used to define this radius.
Crystal structure: The ordered arrangement of atoms, ions, or molecules in a crystalline solid. Interatomic distances in crystals provide experimental data for estimating contact radii.
Space-filling model: A molecular representation in which atom spheres are drawn at sizes proportional to their radii. Its sphere sizes commonly use van der Waals radii to convey molecular volume and packing.
Batsanov radii: A tabulation of atomic and ionic radii compiled by S. S. Batsanov from crystallographic data. Its values provide an alternative compilation, reflecting different data and evaluation choices.
Ionic radius: An effective size assigned to an ion in a crystal, inferred from interionic distances. It describes ions in solids, where charge and coordination change the relevant interatomic distances.
X-ray crystallography: A method that determines crystal structures from the diffraction of X-rays by crystalline samples. Diffraction-derived structures supply many distances used to infer atomic radii.

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