ÁNGSTROM: HISTORY, USES AND EQUIVALENCES - CHEMISTRY - 2024

The angstrom is a unit of length that is used to express the linear distance between two points; especially between two atomic nuclei. Equivalent to 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 Swedish alphabet letter vincing, in honor of the physicist Ander Jonas Ångström (bottom image), who introduced this unit in the course of her 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.

Portrait of Anders Ångström. Source:

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.

History

Emergence of unity

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 from different celestial bodies, discovering that the sun was made of hydrogen (and other elements undergoing nuclear reactions).

A Ångström is due to produce 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, being named after 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.

Visible spectrum

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, their expression in nanometers (nm) or millimicrons equivalent to 10 ^-9 m is also quite common.

The Å and the SI

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 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.

Applications

Atomic radii

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 decimal places.

For example, we have the following atomic radii expressed in angstroms:

-Chloro (Cl), has an atomic radius of 1 Å

-Lithium (Li), 1.52 Å

-Boro (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

-Bromo (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.

Picometer vs Angstrom

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.

Solid State Chemistry and Physics

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.

Furthermore, it is used in electron microscopy to indicate the size of microscopic structures.

Crystallography

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, as all chemical bonds are in the range of 1 to 6 Å.

Wavelengths

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). Wavelength is inversely proportional to the energy and frequency of electromagnetic radiation.

Therefore, the longer the wavelength of electromagnetic radiation, the lower its frequency and energy.

Equivalences

Finally, some equivalences of Å are available with different units, 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 millimicra (nanometer) / Å.

-100 picometer / Å.

References

1. Helmenstine, Anne Marie, Ph.D. (December 05, 2018). Angstrom Definition (Physics and Chemistry). Recovered from: thoughtco.com
2. Wikipedia. (2019). Angstrom. Recovered from: es.wikipedia.org
3. Whitten, Davis, Peck & Stanley. (2008). Chemistry. (8th ed.). CENGAGE Learning.
4. The Regents of the University of California. (nineteen ninety six). Electromagnetic spectrum. Recovered from: cse.ssl.berkeley.edu
5. AVCalc LLC. (2019). What is angstrom (unit). Recovered from: aqua-calc.com
6. Angstrom - The man and the unit.. Recovered from: phycomp.technion.ac.il