Cesium (Cs): properties, applications, accident

O cesium is a metallic element belonging to group 1 of the TThe beauty Perodic. It has a silvery appearance, is reactive with water, and has a number of isotopes. Some of these isotopes are radioactive and have half-lives ranging from years to millions of years. The natural source of cesium is the mineral pollucite, found in large quantities in a certain region of Canada.

O The best-known cesium isotope is cesium-137, which was responsible for the radioactive accident that occurred in Goiânia in 1987.

Despite being toxic to animals and people, when handled correctly, radioactive cesium isotopes bring benefits, being able to be used in the medical area, in Physics and even in the sterilization of sludge and foods.

Read too: Uranium — radioactive element of great importance for energy generation

Summary about cesium

  • Cesium is a rare metallic element, belonging to group 1 of the Periodic Table.

  • Cesium has fusion point relatively low, being able to change from solid to liquid at 28 °C.

  • Cesium is highly reactive with water and readily oxidized by oxygen.

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  • Cesium-133 is the only stable isotope of cesium, with the remaining 39 radioactive isotopes.

  • The main mineral source of cesium is pollucite, whose extraction mines are concentrated in Canada.

  • The main application of cesium is in atomic clocks, which are very high precision time measurement equipment.

  • Cesium also finds application in photoemission devices, in spacecraft propulsion systems in the composition of oil well drilling fluids and in medical equipment and therapies medicinal.

Cesium properties

  • Symbol: Cs.

  • Atomic number: 55.

  • atomic mass: 132.905 u.

  • Electronic configuration: [Xe] 6s¹.

  • physical state: solid (at 20 °C) and liquid (at 28 °C).

  • Fusion point: 28.5°C.

  • Boiling point: 671°C.

  • Density: 1.93 g cm-3.

  • electronegativity: 0.79 (Pauling electronegativity).

  • chemical series: representative elements.

  • Location in Table Perodic: group 1, period 6, block s.

  • isotopes: 133Cs (100%).

characteristics of cesium

Cesium is a metal of rare occurrence belonging to group 1 of the Periodic Table, known as the alkali metal group. Cesium has a silvery-golden appearance, is a soft, ductile metal and has a melting point of approximately 28 °C. Because the melting temperature is relatively low, this element can be found in its liquid state, depending on the ambient temperature.

Glass ampoule containing the element cesium
Glass ampoule containing the element cesium

Like the other alkali metals, cesium reacts violently with water and is so reactive that it can even react with ice at temperatures above -116 °C. In contact with atmospheric air, cesium is readily oxidized. Due to this very reactive nature, its most common form of manipulation is in association with the nitrogen, in the form of cesium azide (CsN). Cesium is stored in metallic form by immersion in nonpolar solvents or in the presence of inert gases.

the cesium has 39 known isotopes. Of these, only cesium-133 (133Cs) is naturally stable. The others have atomic masses that span from 112 to 151 u, and most of them have half life reduced, ranging from fractions of a second to even a few days.

Some radioactive isotopes of cesium can be found in nature, as they are derived from nuclear fission of other elements. The radioisotope cesium-135 (135Cs) has a long half-life on the scale of 2.3 million years. The half-life of cesium-137 (137Cs) is about 30 years old and cesium-134 (134Cs) is just over two years.

At physicochemical properties of cesium are similar to those of potassium It's from rubidium, this last element being one of the contaminants of ores containing cesium.

In the Periodic Table, cesium is located at the lower left end, being the chemical element with the lowest electronegativity.

The compound cesium hydroxide (CsOH) is the strongest base known, being able to attack glass. Other more common cesium compounds are cesium nitrate (CsNO3) and cesium chloride (CsCl), both used industrially to obtain other chemical products.

the cesium is considered a rare element, as it occupies the 45th position among the most abundant elements in the earth's crust, with an estimated amount of 2.6 ppm. the cesium is a toxic and radioactive metal.

Read too: Which chemical elements are radioactive?

Where is cesium found?

O The main mineral known as a source of cesium is pollucite, a hydrated cesium silicate and aluminum, whose molecular formula is CsAlSi2O6. Pollucite contains between 5% and 32% cesium oxide. Lepidolite can also be a source ore for cesium, depending on the extraction site.

Mineral pollutes.
Mineral pollutes.

the region of lAug Bernic, located in Manitoba, Canada, is one of the main sources of cesium on the planet, concentrating around 82% of all existing pollucite in the world, an amount equivalent to 300 thousand tons of ore. It is estimated that the existing pollucite in this region has a composition of approximately 20% in cesium.

There are other reserves containing pollucite in the Zambia and namibia, located on the African continent. Minerals containing cesium have already been recorded in Afghanistan, China, Italy, Tibet and Chile.

Other ores that contain cesium are beryl (Be3Al2(SiO3)6), with about 9% cesium, avogadrite ((K, Cs) BF4), with varying amounts of cesium, and rhodizite (hydrated aluminum, beryllium, sodium and cesium borate of varied composition), containing a maximum content of 3% of cesium. Even so, the only economically viable mineral for the extraction of cesium is pollucite.

Obtaining cesium

the cesium is present in some minerals, such as pollucite, being normally obtained in its impure form. The main contamination in cesium obtained from natural sources is due to the presence of the element rubidium, due to the chemical similarities between these two species.

THE cesium extraction coming of pollucite can be performed by three main methods: acid digestion, alkaline digestion or direct reduction.

Acid digestion is the most used method and is performed at high temperature, and hydrobromic, hydrochloric, sulfuric or hydrofluoric. In this process, a solution containing cesium and impurities is formed, which is purified by hydrolysis, obtaining a cesium salt of high purity.

In alkaline digestion, the mineral pollucite is roasted with a mixture of sodium or calcium salts. By washing the resulting solid with water or dilute ammonia, a higher purity solution of cesium salts is obtained.

In the direct reduction method, the isolation of cesium occurs by crushing and heating the ores containing cesium and rubidium, in the presence of metallic sodium at a temperature of 650 °C. In this process, a metal alloy is formed that is subjected to a separation process known as fractional distillation. In distillation, the temperature of the alloy is gradually increased and, due to the different boiling temperatures of the metals, it is possible to separate them from the mixture and isolate them individually.

Cesium in its metallic form is highly reactive, so it is most commonly its commercialization and manipulation in the form of cesium azide (CsN3), whereby cesium can be recovered by simply heating to approximately 390 °C. Cesium azide is prepared by the reaction between a solution of cesium sulfate and barium azide.

Cesium applications

Cesium's applications are limited due to its low melting point and, therefore, it has very specific uses.

One of the main uses of the element cesium is in atomic clocks.,which are high-precision watches used in timing systems. This type of equipment uses the transition of electrons between two different and well-known levels of the ground state of the cesium atom to define the time unit of second. The use of this type of transition to measure time is due to its stability, the fact that it does not change from atom to atom and does not wear out over time.

Atomic clock based on the transitions of cesium atoms located in a laboratory in Germany. [1]
Atomic clock based on the transitions of cesium atoms located in a laboratory in Germany. [1]

Due to the photoemissive properties, cesium is used in photoelectric and solar cells, imaging devices in televisions and night vision equipment. This element still composes some types of glass in special lenses and optical fiber.

In the chemical industry, cesium is used as a catalyst in organic reactions of hydrogenation and purification methods Petroleum.

Currently, one of the most important applications of this element is in the composition of drilling fluids for the natural gas and oil industries.

In combination with oxygen, it forms a compound used for the removal of waste gases in vacuum tubes.

Cesium ions, due to their high molecular mass, are used in ionic propulsion systems in spacecraft engines.

The radioactive isotope cesium-137 finds application in medicine and industry as an emitter of gamma radiation.

Read too:Curium — synthetic element marked by its great radioactive capacity

Precautions with cesium

Cesium is an element extremely reactive in the presence of water, so it is classified as dangerous, and its transport and storage must be carried out in isolation from other reagents.

In contact with water, cesium gives rise to cesium hydroxide. This compound is a base very strong able to attack the glass.

the cesium has some radioisotopes that are extremely hazardous to health human and animal. O 137Cs is a cause of infertility, cancer, bone marrow and skin damage and can lead to death.

Cesium-137 sample with indication on the package of radioactive substance
Cesium-137 sample with indication on the package of radioactive substance

Cesium ions, because of their chemical similarity to potassium, you can call The potassium receptors in living organisms, inhibiting the functioning of the sodium-potassium pump, a mechanism involved in several biological functions.

Cesium-137 and the accident in Goiânia

Cesium-137 (137Cs) is one of the radioisotopes of the element cesium, having a half-life of about 30 years. As an isotope of cesium, the species 137Cs has the same number of protons (Z = 55) and different number of neutrons. The value “137” describes the sum of protons and neutrons (55 + 82 = 137).

O137Cs is an unstable and radioactive species. This means that its core emits radiation of the type beta, transforming into the chemical element barium-137 (137Ba). This process is represented by the nuclear reaction:


The radiation emitted by the 137Cs is highly harmful to human health, as it is formed by ionizing particles and electromagnetic radiationhere, which penetrate the tissues, leading to a series of complications, including possible alterations in the DNA.

the product of radioactive decay of 137Cs - the 137Ba ― releases gamma-type radiation, which has even deeper penetrating power than beta radiation.

The damage caused by radiation is due to its ability to displace electrons from atoms, forming cations (species with positive), which are highly reactive and capable of promoting severe changes in tissue cells and even in the DNA.

However, when handled with care, the radiation emitted by the 137Cs can be advantageous and, therefore, this chemical species is used in cancer therapies, in some industries, in food sterilization, in sewage treatment and in equipment surgical.

However, the lack of proper instruction can lead to The serious environmental accidents, such as the one that occurred in Goiânia in 1987. On that occasion, two recycling workers found an abandoned radiotherapy equipment, which contained a capsule with cesium-137, in the form of cesium chloride salt (CsCl).

When reselling the metallic equipment for a junkyard, the capsule was opened by the owner of the place, who found a white powder that turned bright blue in the dark. Because of the beauty of the material found, he distributed it to the people of the region. After a few days, the city's health system identified the care of dozens of people with symptoms of contamination by the radioactive element.

Photo of the radioactive source involved in the 1987 accident in Goiânia.
Photo of the radioactive source involved in the 1987 accident in Goiânia. This metallic part belonged to a radiotherapy equipment. [2]

At the time, four people died., and hundreds more have had or have to live with the symptoms of radioactive material poisoning. As cesium chloride is water-soluble and hygroscopic, it easily spread throughout the region, contaminating soils, water, animals and food.

In this episode, about seven tons of atomic waste were isolated in specific buildings to contain the radiation and must remain there for at least 180 years, time required for the concentration of radioactive material to decrease significantly.

Cesium-137 can also be released into the atmosphere through the activation of nuclear weapons and nuclear power plants. One another source of contamination of the environment by cesium-137 was the event that occurred in Chernobyl, in 1986, since this radioactive element is derived from the radioactive decay mechanisms of uranium.

  • Video lessons Cesium-137: the biggest radiological accident in the world

history of cesium

The cesium element was discovered in 1860 by German scientists Robert Wilhelm Bunsen and Gustav Robert Kirchhoff through spectroscopic analysis of water samples. Cesium was the first chemical element to be discovered by spectroscopy.

The result of these analyzes showed two bright blue lines, accompanied by other lines at other wavelengths, associated with the colors red, green and yellow. Because of the blue lines identified in the spectrum, the Scientists used the term “cesium”, a word that means “blue sky”.

Image credits

[1] geogif / shutterstock

[2] Wikimedia Commons (reproduction)

By Ana Luiza Lorenzen Lima
Chemistry teacher

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