|Physical quantity (s)
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|In SI units
|Jonas Ångström is different
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 .