Caesium

  • caesium, 55cs
    some pale gold metal, with a liquid-like texture and lustre, sealed in a glass ampoule
    caesium
    pronunciationm/ (see-zee-əm)
    alternative namecesium (us, informal)
    appearancepale gold
    standard atomic weight ar, std(cs)132.90545196(6)[1]
    caesium in the periodic table
    hydrogen helium
    lithium beryllium boron carbon nitrogen oxygen fluorine neon
    sodium magnesium aluminium silicon phosphorus sulfur chlorine argon
    potassium calcium scandium titanium vanadium chromium manganese iron cobalt nickel copper zinc gallium germanium arsenic selenium bromine krypton
    rubidium strontium yttrium zirconium niobium molybdenum technetium ruthenium rhodium palladium silver cadmium indium tin antimony tellurium iodine xenon
    caesium barium lanthanum cerium praseodymium neodymium promethium samarium europium gadolinium terbium dysprosium holmium erbium thulium ytterbium lutetium hafnium tantalum tungsten rhenium osmium iridium platinum gold mercury (element) thallium lead bismuth polonium astatine radon
    francium radium actinium thorium protactinium uranium neptunium plutonium americium curium berkelium californium einsteinium fermium mendelevium nobelium lawrencium rutherfordium dubnium seaborgium bohrium hassium meitnerium darmstadtium roentgenium copernicium nihonium flerovium moscovium livermorium tennessine oganesson
    rb

    cs

    fr
    xenoncaesiumbarium
    atomic number (z)55
    groupgroup 1: h and alkali metals
    periodperiod 6
    blocks-block
    element category  alkali metal
    electron configuration[xe] 6s1
    electrons per shell2, 8, 18, 18, 8, 1
    physical properties
    phase at stpsolid
    melting point301.7 k ​(28.5 °c, ​83.3 °f)
    boiling point944 k ​(671 °c, ​1240 °f)
    density (near r.t.)1.93 g/cm3
    when liquid (at m.p.)1.843 g/cm3
    critical point1938 k, 9.4 mpa[2]
    heat of fusion2.09 kj/mol
    heat of vaporization63.9 kj/mol
    molar heat capacity32.210 j/(mol·k)
    vapour pressure
    p (pa) 1 10 100 1 k 10 k 100 k
    at t (k) 418 469 534 623 750 940
    atomic properties
    oxidation states−1, +1[3] (a strongly basic oxide)
    electronegativitypauling scale: 0.79
    ionization energies
    • 1st: 375.7 kj/mol
    • 2nd: 2234.3 kj/mol
    • 3rd: 3400 kj/mol
    atomic radiusempirical: 265 pm
    covalent radius244±11 pm
    van der waals radius343 pm
    color lines in a spectral range
    spectral lines of caesium
    other properties
    natural occurrenceprimordial
    crystal structurebody-centred cubic (bcc)
    bodycentredcubic crystal structure for caesium
    thermal expansion97 µm/(m·k) (at 25 °c)
    thermal conductivity35.9 w/(m·k)
    electrical resistivity205 nΩ·m (at 20 °c)
    magnetic orderingparamagnetic[4]
    young's modulus1.7 gpa
    bulk modulus1.6 gpa
    mohs hardness0.2
    brinell hardness0.14 mpa
    cas number7440-46-2
    history
    namingfrom latin caesius, sky blue, for its spectral colours
    discoveryrobert bunsen and gustav kirchhoff (1860)
    first isolation carl setterberg (1882)
    main isotopes of caesium
    iso­tope abun­dance half-life (t1/2) decay mode pro­duct
    133cs 100% stable
    134cs syn 2.0648 y ε 134xe
    β 134ba
    135cs trace 2.3×106 y β 135ba
    137cs syn 30.17 y[5] β 137ba
    category category: caesium
    | references

    caesium (iupac spelling[6]) (also spelled cesium in american english)[note 1] is a chemical element with the symbol cs and atomic number 55. it is a soft, silvery-golden alkali metal with a melting point of 28.5 °c (83.3 °f), which makes it one of only five elemental metals that are liquid at or near room temperature.[note 2] caesium has physical and chemical properties similar to those of rubidium and potassium. the most reactive of all metals, it is pyrophoric and reacts with water even at −116 °c (−177 °f). it is the least electronegative element, with a value of 0.79 on the pauling scale. it has only one stable isotope, caesium-133. caesium is mined mostly from pollucite, while the radioisotopes, especially caesium-137, a fission product, are extracted from waste produced by nuclear reactors.

    the german chemist robert bunsen and physicist gustav kirchhoff discovered caesium in 1860 by the newly developed method of flame spectroscopy. the first small-scale applications for caesium were as a "getter" in vacuum tubes and in photoelectric cells. in 1967, acting on einstein's proof that the speed of light is the most constant dimension in the universe, the international system of units used two specific wave counts from an emission spectrum of caesium-133 to co-define the second and the metre. since then, caesium has been widely used in highly accurate atomic clocks.

    since the 1990s, the largest application of the element has been as caesium formate for drilling fluids, but it has a range of applications in the production of electricity, in electronics, and in chemistry. the radioactive isotope caesium-137 has a half-life of about 30 years and is used in medical applications, industrial gauges, and hydrology. nonradioactive caesium compounds are only mildly toxic, but the pure metal's tendency to react explosively with water means that caesium is considered a hazardous material, and the radioisotopes present a significant health and ecological hazard in the environment.

  • characteristics
  • production
  • history
  • applications
  • health and safety hazards
  • see also
  • notes
  • references
  • external links

Caesium, 55Cs
Some pale gold metal, with a liquid-like texture and lustre, sealed in a glass ampoule
Caesium
Pronunciationm/ (SEE-zee-əm)
Alternative namecesium (US, informal)
Appearancepale gold
Standard atomic weight Ar, std(Cs)132.90545196(6)[1]
Caesium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Rb

Cs

Fr
xenoncaesiumbarium
Atomic number (Z)55
Groupgroup 1: H and alkali metals
Periodperiod 6
Blocks-block
Element category  Alkali metal
Electron configuration[Xe] 6s1
Electrons per shell2, 8, 18, 18, 8, 1
Physical properties
Phase at STPsolid
Melting point301.7 K ​(28.5 °C, ​83.3 °F)
Boiling point944 K ​(671 °C, ​1240 °F)
Density (near r.t.)1.93 g/cm3
when liquid (at m.p.)1.843 g/cm3
Critical point1938 K, 9.4 MPa[2]
Heat of fusion2.09 kJ/mol
Heat of vaporization63.9 kJ/mol
Molar heat capacity32.210 J/(mol·K)
Vapour pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 418 469 534 623 750 940
Atomic properties
Oxidation states−1, +1[3] (a strongly basic oxide)
ElectronegativityPauling scale: 0.79
Ionization energies
  • 1st: 375.7 kJ/mol
  • 2nd: 2234.3 kJ/mol
  • 3rd: 3400 kJ/mol
Atomic radiusempirical: 265 pm
Covalent radius244±11 pm
Van der Waals radius343 pm
Color lines in a spectral range
Spectral lines of caesium
Other properties
Natural occurrenceprimordial
Crystal structurebody-centred cubic (bcc)
Bodycentredcubic crystal structure for caesium
Thermal expansion97 µm/(m·K) (at 25 °C)
Thermal conductivity35.9 W/(m·K)
Electrical resistivity205 nΩ·m (at 20 °C)
Magnetic orderingparamagnetic[4]
Young's modulus1.7 GPa
Bulk modulus1.6 GPa
Mohs hardness0.2
Brinell hardness0.14 MPa
CAS Number7440-46-2
History
Namingfrom Latin caesius, sky blue, for its spectral colours
DiscoveryRobert Bunsen and Gustav Kirchhoff (1860)
First isolation Carl Setterberg (1882)
Main isotopes of caesium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
133Cs 100% stable
134Cs syn 2.0648 y ε 134Xe
β 134Ba
135Cs trace 2.3×106 y β 135Ba
137Cs syn 30.17 y[5] β 137Ba
Category Category: Caesium
| references

Caesium (IUPAC spelling[6]) (also spelled cesium in American English)[note 1] is a chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of 28.5 °C (83.3 °F), which makes it one of only five elemental metals that are liquid at or near room temperature.[note 2] Caesium has physical and chemical properties similar to those of rubidium and potassium. The most reactive of all metals, it is pyrophoric and reacts with water even at −116 °C (−177 °F). It is the least electronegative element, with a value of 0.79 on the Pauling scale. It has only one stable isotope, caesium-133. Caesium is mined mostly from pollucite, while the radioisotopes, especially caesium-137, a fission product, are extracted from waste produced by nuclear reactors.

The German chemist Robert Bunsen and physicist Gustav Kirchhoff discovered caesium in 1860 by the newly developed method of flame spectroscopy. The first small-scale applications for caesium were as a "getter" in vacuum tubes and in photoelectric cells. In 1967, acting on Einstein's proof that the speed of light is the most constant dimension in the universe, the International System of Units used two specific wave counts from an emission spectrum of caesium-133 to co-define the second and the metre. Since then, caesium has been widely used in highly accurate atomic clocks.

Since the 1990s, the largest application of the element has been as caesium formate for drilling fluids, but it has a range of applications in the production of electricity, in electronics, and in chemistry. The radioactive isotope caesium-137 has a half-life of about 30 years and is used in medical applications, industrial gauges, and hydrology. Nonradioactive caesium compounds are only mildly toxic, but the pure metal's tendency to react explosively with water means that caesium is considered a hazardous material, and the radioisotopes present a significant health and ecological hazard in the environment.