Ångström

The ångström is a unit of length equal to 10⁻¹⁰ metre, commonly used for atomic and molecular dimensions and wavelengths of light.

Atomic radius: A measure of the size of an atom, defined differently according to the context and measurement method. Atomic radii are commonly expressed in ångströms because atoms typically span a few tenths of a nanometre.
Metre: The SI base unit of length, defined by fixing the speed of light in vacuum. The ångström is defined as exactly one ten-billionth of a metre.
Anders Jonas Ångström: A Swedish physicist who pioneered spectroscopy and studied the solar spectrum in the nineteenth century. The length unit was named in honor of this spectroscopist.
Bohr radius: The characteristic radius of the hydrogen atom in the Bohr model, about 0.529 ångström. This atomic-scale constant is a physical length, unlike the defined unit ångström.
Covalent radius: Half the distance between two identical atoms joined by a covalent bond, used to estimate atomic size. Covalent radii give a direct ångström-scale measure of bonded atoms.
Nanometre: A unit of length equal to 10⁻⁹ metre. A nanometre is ten times larger than an ångström, a useful conversion for nanoscale structures.
Spectroscopy: The study of how matter interacts with electromagnetic radiation as a function of wavelength or frequency. Spectroscopy helped establish the need for a convenient unit for short wavelengths.
Fermi (unit): A former name for the femtometre, equal to 10⁻¹⁵ metre and used in nuclear physics. The fermi is far smaller than an ångström and applies to nuclear rather than atomic scales.
Bond length: The distance between the nuclei of two chemically bonded atoms. Molecular bond lengths are commonly reported in ångströms.
Picometre: A unit of length equal to 10⁻¹² metre. A picometre is one hundredth of an ångström and is another unit for atomic distances.

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