Caesium

CsCrystals

Rb&Cs crystals

File:Cesium water.theora.ogv

CsCl polyhedra

CsX@DWNT

Caesium (or cesium in American English) is a chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28.5 °C (83.3 °F), which makes it one of only five metallic elements that are liquid at or near room temperature. Caesium is an element in the periodic table that is characterized by its large atomic radius, low ionization energy, and high reactivity, especially in water.

Properties

Caesium is highly reactive and highly explosive in water. It is the most electropositive and alkaline element. The metal is characterized by a spectrum of yellow lines in its flame test. Caesium metal is soft and easily cut with a knife. The metal's low melting point (slightly above room temperature) means it can melt in one's hand.

Occurrence

Caesium is not widely distributed in nature, but it is found in minute amounts in mineral water, and more abundantly in pollucite, a rare mineral. The largest deposits of pollucite, which is the primary source of caesium, are found in Zimbabwe, Canada, and Namibia.

Applications

Caesium has several applications due to its unique properties. It is used in atomic clocks, which are incredibly accurate timekeeping devices. Caesium atomic clocks form the basis for the world's time standard. The element is also used in oil drilling fluids, in electricity generation and transmission, in photoelectric cells, and as a getter in vacuum tubes.

Isotopes

Caesium has at least 39 known isotopes, ranging from Cs-112 to Cs-151. Caesium-133 is the only stable isotope and thus makes up all natural caesium. The radioactive isotope caesium-137, with a half-life of about 30.17 years, is a significant product of nuclear fission and is one of the more problematic elements in nuclear waste.

Health and Safety

Caesium is highly reactive and requires careful handling. It reacts explosively with water and can cause burns on contact with skin. Caesium compounds, especially caesium chloride and caesium nitrate, can be hazardous. Caesium-137, being radioactive, poses a significant health risk and is a major concern in the aftermath of nuclear reactor accidents, such as the Chernobyl disaster.

Environmental Impact

The release of caesium into the environment, primarily caesium-137, can have long-term environmental impacts. It can contaminate soil and water and enter the food chain, posing risks to human health and wildlife. Cleanup and containment of caesium contamination are challenging and costly.