Angstrom

angstrom
The width of a hydrogen atom is about 1.1 angstroms; the width of a proton (in black) is 1.7×10−5 angstroms.
General information
Unit systemNon-SI metric unit
Unit ofLength
SymbolÅ
Named afterAnders 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]) is a unit of length equal to 10−10 m; that is, one ten-billionth of a metre, a hundred-millionth of a centimetre,[7] 0.1 nanometre, or 100 picometres. The unit is named after the Swedish physicist Anders Jonas Ångström (1814–1874).[7] It was originally spelled with Swedish letters, as Ångström[7] and later as ångström (/ˈɒŋstrəm/).[8][9][10] The latter spelling is still listed in some dictionaries,[1] but is now rare in English texts. Some popular US dictionaries list only the spelling angstrom.[2][3]

The unit's symbol is Å, which is a letter of the Swedish alphabet, regardless of how the unit is spelled.[1][4] However, "A"[3] or "A.U."[11][7] may be used in less formal contexts or typographically limited media.

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] 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.[7] It was only in 1960, when the metre was redefined in the same way, that the angstrom became again equal to 10−10 metre. Yet the angstrom was never part of the SI system of units,[13][14] and has been increasingly replaced by the nanometre (10−9 m) or picometre (10−12 m).

  1. ^ a b c Cite error: The named reference oxfo2019 was invoked but never defined (see the help page).
  2. ^ a b Cite error: The named reference webs2024 was invoked but never defined (see the help page).
  3. ^ a b c d Cite error: The named reference collins was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference webs1989 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference well2008 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference roac2011 was invoked but never defined (see the help page).
  7. ^ a b c d e Cite error: The named reference oxfo1986 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference bipm8 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference iupac was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference thom2009 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference brag1921 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference vail2015 was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference bipm9 was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference nist2019 was invoked but never defined (see the help page).
This article is issued from Wikipedia. The text is available under Creative Commons Attribution-Share Alike 4.0 unless otherwise noted. Additional terms may apply for the media files.