Ångström (unit)
Physical unit | |
---|---|
Unit name | Ångström |
Unit symbol | |
Physical quantity (s) | length |
Formula symbol | , , , |
dimension | |
In SI units | |
Named after | Jonas Ångström is different |
Derived from | Atomic radius |
The Ångström [ ˈɔŋstrø: m ] (after the Swedish physicist Anders Jonas Ångström ) is a unit of length . The unit symbol is Å ( A with a ring ). One Ångström is equal to ten millionth of a millimeter . The Ångström is not an SI unit.
The Ångström is used in particular in crystallography and chemistry to be able to work with "simple" numerical values. 1 Å is the typical order of magnitude for atomic radii and distances between atoms in crystal structures and bond lengths in molecules . The radius of isolated neutral atoms is between 0.3 and 3 Å. Therefore, the angstrom is often used as a unit for distances on an atomic scale, e.g. B. for the thickness of very thin layers , for specifying the wavelength of the X-ray radiation used in their determination in X-ray diffraction experiments such as crystal structure analysis, and for the pore size of stationary phases in liquid chromatographic columns for high-performance liquid chromatography (HPLC).
In thermodynamics , the mean free path of moving molecules is often given in angstroms. It is also used in optics and astronomy to specify a wavelength (although less in German-language, but more in English-language specialist publications).
In 1925 Manne Siegbahn made a similar attempt to come up with easily manageable numerical values with the definition of the X-unit , which corresponded to about 10 −13 meters. But the Ångström prevailed.
Since the Ångström is not listed in the Units Directive, it is not a legal unit in the EU , nor in Switzerland according to the Swiss Units Ordinance. In DIN 1301-3 it is explicitly listed as a no longer permitted unit.
Representation in computer systems
According to the Unicode standard, the unit of length Ångström should be represented by the capital letter Å ( U+00C5
). Unicode also contains a character called ANGSTROM SIGN (Ångström character ,:U+212B
Å), but this was only included for compatibility with older character coding standards and should not be used in newly created texts .
Web links
Individual evidence
- ↑ Duden: Large foreign dictionary. ISBN 978-3-411-04163-3 , entry "Ångström", p. 102.
- ↑ Packs for chromatography columns. Retrieved May 30, 2018 .
- ↑ Unicode Consortium: The Unicode Standard, Version 5.0. (PDF) 2007, p. 493 , accessed on December 28, 2016 (English).