Global InformationAngstrom information
| angstrom | |
|---|---|
| Unit system | Non-SI metric unit |
| Unit of | Length |
| Symbol | Å |
| Named after | Anders Jonas Ångström |
| Conversions | |
| 1 Å in ... | ... is equal to ... |
| SI Units | 10−10 m = 0.1 nm |
| CGS Units | 10−8 cm |
| Imperial units | 3.937008×10−9 in |
| Planck units | 6.187×1024 lP |
The angstrom[1][2][3][4] (/ˈæŋstrəm/;[3][5][6] ANG-strəm[5]) or ångström (/ˈɒŋstrəm/)[7][1][8][9][10] is a metric unit of length equal to 10−10 m; that is, one ten-billionth (US) of a metre, a hundred-millionth of a centimetre,[11] 0.1 nanometre, or 100 picometres. Its symbol is Å, a letter of the Swedish alphabet. The unit is named after the Swedish physicist Anders Jonas Ångström (1814–1874).[11]
The angstrom is often used in the natural sciences and technology to express sizes of atoms, molecules, microscopic biological structures, and lengths of chemical bonds, arrangement of atoms in crystals,[12][13] wavelengths of electromagnetic radiation, and dimensions of integrated circuit parts. 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 (monochromatic components of the emission spectrum) of chemical elements. However, they soon realized that the definition of the metre at the time, based on a material artifact, was not accurate enough for their work. So, around 1907 they defined their own unit of length, which they called "Ångström", based on the wavelength of a specific spectral line.[11] It was only in 1960, when the metre was redefined in the same way, that the angstrom became again equal to 10−10 metre.
Even though it is a decimal power fraction of the metre, the angstrom was never part of the SI system of units,[14][15] and it has been increasingly replaced by the nanometre or picometre. Up to 2019, it was listed as a compatible unit by both the International Bureau of Weights and Measures (BIPM) and the US National Institute of Standards and Technology (NIST),[9][10] but it is not mentioned in the 9th edition of the official SI document, the "BIPM Brochure" (2019)[14] or in the NIST version of the same.[15]
The 8th edition of the BIPM brochure (2006)[9] and the NIST guide 811 (2008)[10] used the spelling ångström, with Swedish letters; however, this form is rare in English texts. Some popular US dictionaries list only the spelling angstrom.[2][3]
The accepted symbol is "Å", no matter how the unit is spelled.[1][4][3] However, "A" is often used in less formal contexts or typographically limited media.[citation needed]
- ^ a b c "angstrom | Definition of angstrom in English by Oxford Dictionaries". 2019-03-06. Archived from the original on 2019-03-06. Retrieved 2024-01-30.
- ^ a b "Definition of ANGSTROM". www.merriam-webster.com. Retrieved 2024-01-30.
- ^ a b c d "Angstrom". Collins English Dictionary. Retrieved 2019-03-02.
- ^ a b Webster's Encyclopedic Unabridged Dictionary of the English Language. Portland House, 1989
- ^ a b Wells, John C. (2008), Longman Pronunciation Dictionary (3rd ed.), Longman, ISBN 9781405881180
- ^ Roach, Peter (2011), Cambridge English Pronouncing Dictionary (18th ed.), Cambridge: Cambridge University Press, ISBN 9780521152532
- ^ Oxford dictionary of English. Oxford [England]; New York: Oxford University Press. 2010. p. 61. ISBN 978-0-19-957112-3. Archived from the original on May 3, 2023.
- ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "Ångström". doi:10.1351/goldbook.N00350
- ^ a b c International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), p. 127, ISBN 92-822-2213-6, archived (PDF) from the original on 2021-06-04, retrieved 2021-12-16
- ^ a b c Ambler Thompson and Barry N. Taylor (2009): "B.8 Factors for Units Listed Alphabetically". NIST Guide to the SI, National Institutes of Standards and Technology. Accessed on 2019-03-02
- ^ a b c Entry "angstrom" in the Oxford English Dictionary, 2nd edition (1986). Retrieved on 2021-11-22 from https://www.oed.com/oed2/00008552 Archived 2021-11-22 at the Wayback Machine.
- ^ Arturas Vailionis (2015): "Geometry of Crystals" Lecture slides for MatSci162_172, Geometry; Stanford University. archived on 2015-03-19
- ^ "ICSD". Archived from the original on 2014-07-30. Retrieved 2015-01-30.
- ^ a b Bureau international des poids et measures (2019): Le système international d'unités, complete brochure, 9th edition.
- ^ a b NIST (2019): Special Publication 330: The International System of Units (SI) 2019 Edition.