Cesium

Cesium

Cesium (chemical symbol Cs, atomic number 55) is a soft, gold-colored, alkali metal. It is one of the most reactive elements and is notable for its low melting point of 28.5 °C (83.3 °F), which allows it to melt in the palm of your hand. Cesium is used in a variety of applications, from atomic clocks to medical imaging.

Properties

Cesium is a member of the alkali metals group, which includes lithium, sodium, potassium, rubidium, and francium. It is characterized by its softness, ductility, and its ability to conduct electricity. Cesium is highly reactive, especially with water, and must be stored in mineral oil or an inert atmosphere to prevent it from reacting with moisture in the air.

Physical Properties

• Atomic number: 55
• Atomic weight: 132.90545196 u
• Density: 1.93 g/cm³
• Melting point: 28.5 °C (83.3 °F)
• Boiling point: 671 °C (1240 °F)

Chemical Properties

Cesium reacts explosively with water, producing cesium hydroxide (CsOH) and hydrogen gas. It also reacts with oxygen to form cesium oxide (Cs₂O). Due to its high reactivity, cesium is used in various chemical applications, including as a getter in vacuum tubes.

Occurrence

Cesium is relatively rare in the Earth's crust, with an abundance of approximately 3 parts per million. It is primarily found in the mineral pollucite, which is mined in countries such as Canada and Zimbabwe. Cesium is also found in trace amounts in lepidolite, a lithium-rich mica.

Applications

Cesium has several important applications:

• Atomic Clocks: Cesium is used in atomic clocks, which are the most accurate timekeeping devices available. The International System of Units (SI) defines the second based on the frequency of radiation emitted by cesium-133 atoms.

• Medical Imaging: Radioactive isotopes of cesium, such as cesium-137, are used in radiotherapy for cancer treatment and in industrial radiography to inspect welds and metal parts.

• Oil Drilling: Cesium formate brines are used in oil drilling fluids due to their high density and low viscosity, which help to stabilize the wellbore.

Safety and Handling

Due to its high reactivity, cesium must be handled with care. It can cause burns upon contact with skin and is highly flammable. Cesium compounds, particularly radioactive isotopes, pose health risks and require appropriate safety measures.

Isotopes

Cesium has 39 known isotopes, with cesium-133 being the only stable isotope. Cesium-137 is a notable radioactive isotope with a half-life of about 30 years, commonly used in medical and industrial applications.

See Also

• Alkali metal
• Atomic clock
• Radioactive decay

References

• Greenwood, N. N., & Earnshaw, A. (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann.
• Emsley, J. (2011). Nature's Building Blocks: An A-Z Guide to the Elements. Oxford University Press.