Cesium is a special metal because it is part of the group of only five metallic elements that are liquid at normal temperatures. In pure form, it looks like a shiny consistent liquid with a silver metallic color.
Cesium has the atomic number 55 in the periodic table of elements and it is classified as an alkali metal. It has a very soft texture, even when in solid form. It is one of the rare elements on Earth and the crust only includes 3ppm in its structure. Cesium has a number of industrial uses, especially as compounds formed after reacting with water or the oxygen in the air.
Despite its rarity, cesium has many industrial applications due to its unique chemical properties. Many of its isotopes are known to be radioactive. It is very rarely found in pure form in nature, because it quickly reacts with other elements. Most of it is produced through nuclear fission or refined from a few minerals. Cesium and its radioactive isotopes are mostly used in science and technology, but there are also a few common products that include it in their structure.
This metal has the very strange feature of being in a liquid state at room temperature. It has a silvery white color and very low durability, even in solid form. It is strongly alkaline and electropositive, with a high chemical reactivity. The reaction between pure cesium and water can be quite violent. In the table of elements, it is designated as Cs. Due to its high reactivity, it is found in many chemical compounds. Some of these are toxic to humans.
Gustav Kirchoff and Robert Bunsen were the first to discover cesium in 1860. They were studying mineral water from the source in the German town of Durkheim, using a spectrometer. They noticed the presence of a bluish grey line on the spectrum, which was emitted by an unknown element. They named it based on the bluish grey color after the ancient Latin word caesius, which designates this particular nuance. The element was only isolated in pure form in 1882. It retains the name caesium in British English scientific works.
The main industrial uses of cesium are nuclear medicine, photoelectric cells and very precise atomic clocks. Some cancer radiotherapy treatments are based on cesium isotopes. This metal is also needed in some chemistry and scientific applications as a catalyst for other reactions. While pure cesium is an expensive metal due to its rarity, some of the compounds are quite reasonably priced.
Nuclear bombs can release cesium isotopes in the air when they explode, with nuclear waste material being the second main source of contamination. They end up in rivers and eventually in drinking water. When ingested, cesium isotopes are very dangerous and can even be lethal in high doses or after long periods of exposure. However, this metal is only toxic in high concentrations that are rarely encountered, so poisoning cases are uncommon. Cesium must be handled with care, not only because it is toxic but also due to its very high reactivity with water and air.
The group of alkali metals also includes lithium, sodium, potassium, rubidium and francium. All of them have a single electron in the exterior shell, which makes them very reactive. As a result, they are rarely found in elemental form in nature. They share a number of other common traits: they are excellent heat and power conductors, with a soft and ductile structure.
One special use for cesium is the production of atomic clocks due to its extreme accuracy. One atom of cesium vibrates exactly 9,192,631,770 times between energy levels in one second. While the accuracy of cesium is not perfect, it would take 100 million years for an atomic clock to lose a single second.
Cesium is very rarely found on Earth, with a concentration of no more than 3 in one million parts. Compared to the other periodic table elements, it the 50th most common. It is a lot rarer in the solar system as a whole, where cesium only represents 8 parts per billion of the total weight.
Many elements react quickly with cesium, especially gases like oxygen but also non-metals and other compounds with high reactivity.
The reaction with water is very violent and cesium is treated like a dangerous material. Even the moisture in the air is enough to start such a reaction, so it is usually stored in a vacuum or protected by a layer of mineral oil or kerosene. Many other chemicals also react strongly with this metal. These include all halogens, as well as various acids, sulfur and phosphorous.
The fission of uranium in fuel rods of nuclear power plants is the most common source of cesium radioactive isotopes. However, they are also released through the detonation of nuclear bombs.
A number of rare minerals found especially in Canada and Zimbabwe include very low amounts of cesium. The richest of all is pollucite, which has a cesium content between 34 and 42 percent. A much lower amount can be extracted from lepidolite.
Three methods are known to extract cesium from these minerals. The most common is acid digestion, which uses acids to turn all metals into salts that can be separated afterwards. Alkaline digestion is a similar method; just that a solution based on sodium or calcium is used instead of acids to generate salts. Finally, the ore can be heated in a vacuum with calcium, potassium, or sodium, which will separate cesium as an impurity, a technique known as direct reduction.
Trace amounts of cesium are found in nature and humans are exposed to them through food, water or air. The normal amounts are very low and cause no noticeable health effects. However, there are a number of cesium compounds and radioactive isotopes that are highly toxic. They can cause various health issues like bleeding, cell damage, nausea or vomiting.
The cesium found in nature is stable and doesn't emit radiation. The radioactive isotopes are artificial, being produced in labs, and both types are needed for medical purposes.
The so-called "high pH cancer therapy" is based on ingesting cesium in order to control the disease. Even if the stable isotope of cesium is used, this therapy is considered very risky. Tumour cells are considered to be highly acidic, so the supporters of this therapy claim that it can fight tumours by reducing their pH. There is so far no scientific evidence for these claims. First of all, the pH of tumours seems to be the same as the one of normal cells. Cesium doesn't appear to have any effect on cell pH anyway.
There is however some early study evidence suggesting that cesium reduces the risk of death for some cancer types. The mechanism of action is unknown. Another medical use for the stable cesium isotope is in the treatment of depression.
Cesium-137, which is one of the radioactive isotopes of the metal, is sometimes used in radiotherapy cancer treatments. It also has some industrial uses, especially since it can measure liquid flow and the moisture of materials, so it is included in some instruments.
Cesium has limited practical uses, since it has the second lowest melting temperature of all metals. Its main use is the very high reactivity; it combines quickly with oxygen and can eliminate trace gases from vacuum tubes by combining with them. It serves as a catalyst in hydrogenation reactions that involve some organic chemicals. It is also an important material in photoelectric panels and atomic clocks. Cesium ions are a propellant option in the ion engines of space vessels, since it has a relatively high mass and can be ionized quickly.
The reaction between cesium and water in any form, including ice, is violent. The result is cesium hydroxide (CsOH), which is the strongest of all base chemicals and can destroy glass. The most common compounds of cesium are chloride (CsCl) and nitrate (CsNO3), which serve as ingredients in various industrial processes.
Cesium has a number of other industrial uses, in the production of IR lamps, photoelectric cells and vacuum tubes, as well as a catalyst in reactions of organic compound hydrogenation.
The ion propulsion systems can be extremely effective when cesium is used. While they only work in space and not in the atmosphere of Earth, cesium ion engines are the best and can generate a lot more power than the one based on rubidium. A cesium ion thruster is at least 140 times more effective in space than any other alternative.