Angstrom (A)
The ångström (symbol Å) is a unit of length equal to 10-10 meters, or 0.1 nanometers. Named after Swedish physicist Anders Jonas Ångström, it is used primarily in atomic physics, chemistry, and crystallography for measuring atomic radii, bond lengths, and wavelengths of electromagnetic radiation. A single hydrogen atom has a diameter of about 1.2 Å.
Definition
One ångström equals exactly 10-10 meters, 0.1 nanometers, 100 picometers, or approximately 3.937 × 10-9 inches. The SI does not officially recognise the ångström, recommending nanometers (nm) or picometers (pm) instead. However, many scientific journals continue to accept Å in crystallographic and spectroscopic contexts.
History
Anders Jonas Ångström introduced the unit in 1868 in his atlas of the solar spectrum, choosing 10-10 meters as a convenient size for expressing wavelengths of visible light (roughly 4,000-7,000 Å). The unit quickly became standard in spectroscopy and was widely adopted by physicists and chemists. Although the SI system does not include the ångström (preferring nanometers and picometers), it remains in widespread use in crystallography, materials science, and atomic physics because atomic dimensions fall naturally into the 1-10 Å range.
Common Uses
X-ray crystallography reports interatomic distances and crystal lattice parameters in ångströms. Protein Data Bank (PDB) structures list atomic coordinates in ångströms. Wavelengths of visible light range from about 3,800 Å (violet) to 7,500 Å (red). Semiconductor manufacturing specifies thin film thicknesses in ångströms. Atomic radii and covalent bond lengths in chemistry textbooks are typically given in ångströms.
Did You Know? Facts About Angstrom
- Visible light wavelengths range from about 3,800 Å (violet) to 7,500 Å (red).
- A water molecule is about 2.75 Å wide, and a carbon-carbon single bond is 1.54 Å long.
- The ångström symbol Å is a Swedish letter - it is A with a ring above, not a degree symbol.
- The Protein Data Bank, containing over 200,000 molecular structures, uses ångströms as its standard unit for atomic coordinates.
- Anders Ångström was one of the founders of spectroscopy and used his unit to map 1,000 spectral lines of the Sun.