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The atomic (covalent) radii of phosphorus, sulfur, and chlorine are about 1 angstrom, while that of hydrogen is about 0.5 angstroms. Visible light has wavelengths in the range of 4000–7000 Å. In the late 19th century, spectroscopists adopted 10 −10 of a metre as a convenient unit to express the wavelengths of characteristic spectral lines ...
The Angstrom exponent is inversely related to the average size of the particles in the aerosol: the smaller the particles, the larger the exponent. For example, cloud droplets are usually large, and thus clouds have very small Angstrom exponent (nearly zero), and the optical depth does not change with wavelength.
Unit cell definition using parallelepiped with lengths a, b, c and angles between the sides given by α, β, γ [1]. A lattice constant or lattice parameter is one of the physical dimensions and angles that determine the geometry of the unit cells in a crystal lattice, and is proportional to the distance between atoms in the crystal.
Ionic radius, r ion, is the radius of a monatomic ion in an ionic crystal structure. Although neither atoms nor ions have sharp boundaries, they are treated as if they were hard spheres with radii such that the sum of ionic radii of the cation and anion gives the distance between the ions in a crystal lattice.
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 (r 1, r 2 and r 3 below), in a purely operational ...
Molecules with a polar surface area of greater than 140 angstroms squared (Å 2) tend to be poor at permeating cell membranes. [1] For molecules to penetrate the blood–brain barrier (and thus act on receptors in the central nervous system), a PSA less than 90 Å 2 is usually needed. [2] TPSA is a valuable tool in drug discovery and development.
The van der Waals radius, r w, of an atom is the radius of an imaginary hard sphere representing the distance of closest approach for another atom. It is named after Johannes Diderik van der Waals, winner of the 1910 Nobel Prize in Physics, as he was the first to recognise that atoms were not simply points and to demonstrate the physical consequences of their size through the van der Waals ...
(Top) Diamond crystal structure, depicting an atomic spacing of 0.154 nm.(Bottom) Graphite crystal structure, depicting an atomic spacing of 0.142 nm. Atomic spacing refers to the distance between the nuclei of atoms in a material.