The angstrom is a unit of length that is used to express the linear distance between two points; especially between two atomic nuclei. Equals 10-8 cm or 10-10 m, less than one billionth of a meter. Therefore, it is a unit used for very small dimensions. It is represented by the letter of the Swedish alphabet Å, in honor of the physicist Ander Jonas Ångström (bottom image), who introduced this unit in the course of his research.
The angstrom finds use in various fields of physics and chemistry. Being such a small length measurement, it is invaluable in accuracy and convenience in atomic ratio measurements; such as atomic radius, bond lengths, and wavelengths of the electromagnetic spectrum.
Although in many of its uses it is relegated by SI units, such as the nanometer and picometer, it is still valid in areas such as crystallography, and in the studies of molecular structures..
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Anders Jonas Ångström was born in Lödgo, a Swedish town, on August 13, 1814, and died in Uppsala (Sweden), on June 21, 1874. He developed his scientific research in the field of physics and astronomy. He is considered one of the pioneers in the study of spectroscopy.
Ångström investigated heat conduction and the relationship between electrical conductivity and thermal conductivity.
Through the use of spectroscopy, he was able to study the electromagnetic radiation of different celestial bodies, discovering that the sun was made of hydrogen (and other elements undergoing nuclear reactions).
A Ångström is owed the creation of a map of the solar spectrum. This map was elaborated in such detail that it comprises a thousand spectral lines, in which he used a new unit: Å. Subsequently, the use of this unit became widespread, named in honor of the person who introduced it.
In 1867, Ångström examined the spectrum of electromagnetic radiation from the northern lights, discovering the presence of a bright line in the green-yellow region of visible light..
In 1907, Å was used to define the wavelength of a red line that emits cadmium, its value being 6,438.47 Å.
Ångström considered it convenient to introduce the unit to express the different wavelengths that make up the spectrum of sunlight; especially in the region of visible light.
When a ray of sunlight is incident on a prism, the emerging light is broken down into a continuous spectrum of colors, ranging from violet to red; going through indigo, green, yellow and orange.
Colors are an expression of the different lengths present in visible light, between approximately 4,000 Å and 7,000 Å.
When a rainbow is observed, it can be detailed that it is made up of different colors. These represent the different wavelengths that make up visible light, which is decomposed by the drops of water that pass through the visible light..
Although the different wavelengths (λ) that make up the spectrum of sunlight are expressed in Å, it is also quite common to express them in nanometers (nm) or millimicras that are equivalent to 10-9 m.
Although the unit Å has been used in numerous investigations and publications in scientific journals and in textbooks, it is not registered in the International System of Units (SI).
Along with the Å, there are other units, which are not registered in the SI; However, they continue to be used in publications of a different nature, scientific and commercial..
The unit Å is used to express the dimension of the radius of the atoms. The radius of an atom is obtained by measuring the distance between the nuclei of two continuous and identical atoms. This distance is equal to 2 r, so the atomic radius (r) is half of it.
The radius of the atoms oscillates around 1 Å, so it is convenient to use the unit. This minimizes the errors that can be made with the use of other units, since it is not necessary to use powers of 10 with negative exponents or figures with a large number of decimals.
For example, we have the following atomic radii expressed in angstroms:
-Chlorine (Cl), has an atomic radius of 1 Å
-Lithium (Li), 1.52 Å
-Boron (B), 0.85 Å
-Carbon (C), 0.77 Å
-Oxygen (O), 0.73 Å
-Phosphorus (P), 1.10 Å
-Sulfur (S), 1.03 Å
-Nitrogen (N), 0.75 Å;
-Fluorine (F), 0.72 Å
-Bromine (Br), 1.14 Å
-Iodine (I), 1.33 Å.
Although there are chemical elements with an atomic radius greater than 2 Å, among them:
-Rubidium (Rb) 2.48 Å
-Strontium (Sr) 2.15 Å
-Cesium (Cs) 2.65 Å.
It is usual in chemistry texts to find atomic radii expressed in picometers (ppm), which are one hundred times smaller than an angstrom. The difference is simply multiplying the above atomic radii by 100; for example, the atomic radius of carbon is 0.77 Å or 770 ppm.
Å is also used to express the size of a molecule and the space between the planes of an atom in crystal structures. Because of this Å is used in solid state physics, chemistry, and crystallography..
In addition, it is used in electron microscopy to indicate the size of microscopic structures..
The unit Å is used in crystallography studies that use X-rays as a basis, since these have a wavelength between 1 and 10 Å.
The Å is used in positron crystallography studies in analytical chemistry, since all chemical bonds are in the range of 1 to 6 Å.
The Å is used to express the wavelengths (λ) of electromagnetic radiation, especially in the region of visible light. For example, the color green corresponds to a wavelength of 4,770 Å, and the color red a wavelength of 6,231 Å.
Meanwhile, ultraviolet radiation, close to visible light, corresponds to a wavelength of 3,543 Å.
Electromagnetic radiation has several components, including: energy (E), frequency (f), and wavelength (λ). The wavelength is inversely proportional to the energy and frequency of electromagnetic radiation.
Therefore, the greater the wavelength of an electromagnetic radiation, the lower its frequency and energy..
Finally, some equivalences of Å with different units are available, which can be used as conversion factors:
-10-10 meter / Å
-10-8 centimeter / Å
-10-7 mm / Å
-10-4 micrometer (micron) / Å.
-0.10 millimicron (nanometer) / Å.
-100 picometer / Å.
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