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The angstrom is a unit of length that is equal to one ten billionth of a meter , that is, it represents the length of one meter divided by ten billion. Numerically it is 0.0000000001 m, or in scientific notation, 10 -10 m. Just as the meter is represented by the letter m , the angstrom is represented, in most scientific and technical literature, by the symbol Å .
1 Å = 10 -10 m
Uses of the Angstrom
The angstrom is a very small unit of length that is convenient, among other things, for representing the dimensions of atomic and subatomic particles, bond lengths, and crystal structure in the solid state. It is also used to express the wavelengths of X-rays, infrared radiation, and all intermediate wavelengths including visible light, as shown below:
| physical quantity | typical values |
| Wavelengths of electromagnetic radiation | X-rays – from 1 to 100 Å Visible light – from 4,000 to 7,000 Å Infrared light – from 10,000 Å to more than 100,000 Å |
| Atomic and ionic radii | Atomic radius of Helium (The smallest) = 0.31 Å Atomic radius of Cesium (The largest) = 2.65 Å Ionic radius of Iron III (Fe 3+ ) = 0.64 Å |
| link lengths | H – H bond (the shortest known) = 0.74 Å Bi – I bond (the longest known) = 2.81 Å |
| Cell parameters in crystalline solids | NaCl cell parameters: a = b = c = 5.65 Å |
| microscopic biological structures | The thickness of the cell membrane is in the range of 60 to 100 Å |
History of the angstrom as a unit of physics and chemistry
The angstrom is created in honor of Anders Jonas Ångström , a prominent Swedish physicist and astronomer who spent part of his career studying solar radiation. In 1868, when constructing a graph of the intensity of the different rays of the sun in relation to their wavelengths, that is, the electromagnetic spectrum of sunlight, Ångström represented these wavelengths as multiples of one billionth of a millimeter. . This was done with the intention of being able to represent the wavelengths of visible light with sufficient precision without the need to use decimals. The predecessor body of the current International Astronomical Union coined the term angstrom for that unit of length.
Despite its origin as a submultiple of the meter, problems with the official definition of the latter forced a redefinition of the angstrom. And it is that, defined according to the meter, the margin of error of the angstrom was greater than the measurement itself. For this reason, in 1907 it was defined in terms of the wavelength of the red line of emission of cadmium, instead of in relation to the meter. Eventually, in 1960, the meter itself was redefined in spectroscopic terms as well, allowing the angstrom to be redefined in its original form, as it is accepted today.
The Angstrom and the International System of Units
Despite being a submultiple of the meter, and its widespread use in various disciplines, the angstrom does not belong to the international system of units (SI) . It is recognized as a unit of length in such a system, but its use is not recommended. Instead, the use of other units of magnitudes similar to or derived from the main ones is suggested, such as the nanometer (nm, 10 -9 m ) or the picometer (pm, 10 -12 m). On the other hand, it is recognized as part of the metric system of units, since it is directly related to the meter.
Equivalence with other units
The angstrom can be transformed to any other unit of length using the appropriate conversion factor . In addition to the relationship between the angstrom and the meter mentioned at the beginning of this article, here are some other equivalencies that can be useful to carry out quick unit conversions:
| Equivalences between the angstrom and other units | Equivalence between other units and the angstrom |
| 1 Å = 0.000 000 000 1 m = 10 -10 m | 1 m = 10,000,000,000 Å = 10 10 Å |
| 1 Å = 0.000 000 1mm = 10 -7mm | 1mm = 10,000,000 Å = 10 7 Å |
| 1 Å = 0.000 1 μm = 10 -4 μm | 1 μm = 10,000 Å = 10 4 Å |
| 1Å = 0.1nm = 10 -1nm | 1nm = 10Å |
| 1 Å = 100 pm = 10 2 pm | 1 pm = 0.01 Å = 10 -2 Å |
Sources
- International Bureau of Weights and Measures. The International System of Units (SI) (8th ed.). 2006, p. 127. ISBN 92-822-2213-6.
- Chang, R. Chemistry (9th ed.). 2007. ISBN 0-07-298060-5
