vanderWaalsRadien

The van der Waals radius is a measure of the size of an atom or ion, defined as the radius of an imaginary sphere that represents the distance of closest approach between two atoms of the same element that are not chemically bonded. This concept was introduced by Dutch physicist Johannes Diderik van der Waals in 1873 to account for the finite size of gas molecules, which classical physics had previously treated as point particles. The van der Waals radius differs from the covalent radius, which describes the distance between bonded atoms of the same element, as it reflects the space occupied by an atom when it is not chemically interacting with another atom.

Van der Waals radii are typically determined experimentally through crystallographic data, where the shortest distances between non-bonded atoms in a crystal lattice are measured. These values are crucial for understanding molecular packing, predicting crystal structures, and estimating molecular volumes. Unlike ionic radii, which vary depending on the charge of the ion, van der Waals radii are generally considered constant for a given element under standard conditions.

The van der Waals radius varies across the periodic table, generally increasing with atomic size. For example, hydrogen has a van der Waals radius of approximately 120 pm, while larger atoms like iodine have a radius of around 198 pm. These values are essential in fields such as materials science, chemistry, and biochemistry, where molecular interactions and spatial arrangements play a key role. The concept also helps explain phenomena like non-bonded interactions, such as van der Waals forces, which contribute to physical properties like boiling points and solubility.