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Caesium

Caesium (also spelled cesium in American English) is a chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal and one of the most reactive and electropositive elements in the periodic table.

Properties

  • Appearance: Soft, silvery-gold metal that becomes liquid just above room temperature (melting point ~28.5°C or 83.3°F).
  • Reactivity: Highly reactive, especially with water, where it reacts explosively to form caesium hydroxide and hydrogen gas.
  • Density: Low-density metal (1.93 g/cm³).
  • Conductivity: Excellent electrical conductor.
  • Isotopes: The most common and stable isotope is caesium-133.

Uses

  1. Atomic Clocks: Caesium is used in caesium atomic clocks, which are among the most accurate timekeeping devices in the world. These clocks define the International System of Units (SI) second based on the frequency of the microwave spectral line emitted by caesium-133 atoms.
  2. Electronics: Found in photoelectric cells and vacuum tubes due to its low ionization potential.
  3. Oil Exploration: Caesium formate, a heavy brine solution, is used as a drilling fluid in oil and gas exploration.
  4. Research and Medicine: Isotopes like caesium-137 are used in cancer treatment and as a gamma-ray source in industrial radiography.

Discovery

  • Discovered By: Robert Bunsen and Gustav Kirchhoff in 1860 using flame spectroscopy.
  • Name Origin: Derived from the Latin word caesius, meaning “sky blue,” due to the bright blue spectral lines observed in its emission spectrum.

Handling and Safety

  • Reactivity: Must be handled with care, as it reacts violently with water and air. It is stored under inert gases or mineral oil to prevent oxidation.
  • Toxicity: Some caesium compounds are toxic, requiring proper precautions during use.

Abundance

Caesium is relatively rare and occurs in minerals such as pollucite and lepidolite. Major deposits are found in Canada, Zimbabwe, and Namibia.

British vs. American Spelling

The term caesium is commonly used in British English, while cesium is the American English spelling. Despite the spelling difference, both terms refer to the same element and are widely recognized in scientific contexts.

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