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Caesium - Barium

Full table
Name, Symbol, NumberCaesium, Cs, 55
Series Alkali metals
Group, Period, Block1(IA), 6 , s
Density, Hardness 1879 kg/m3, 0.2
Appearance silvery gold
Atomic Properties
Atomic weight 132.90545 amu
Atomic radius (calc.) 260 (298) pm
Covalent radius 225 pm
van der Waals radius no data pm
Electron configuration [Xe]6s1
e- 's per energy level2, 8, 18, 18, 8, 1
Oxidation states (Oxide) 1 (strong base)
Crystal structure Cubic body centered
Physical Properties
State of matter solid
Melting point 301.59 K (83.19 F)
Boiling point 944 K (1240 F)
Molar volume 70.94 ×10-3 m3/mol
Heat of vaporization 67.74 kJ/mol
Heat of fusion 2.092 kJ/mol
Vapor pressure 2.5 kPa
Speed of sound no data
Electronegativity 0.79 (Pauling scale)
Specific heat capacity 240 J/(kg*K)
Electrical conductivity 4.89 106/m ohm
Thermal conductivity 35.9 W/(m*K)
1st ionization potential 375.7 kJ/mol
2nd ionization potential 2234.3 kJ/mol
3rd ionization potential 3400 kJ/mol
Most Stable Isotopes
isoNAhalf-life DMDE MeVDP
133Cs100%Cs is stable with 78 neutrons
134Cs{syn.}2.0648 yepsilon
135Cstrace23 ×106 ybeta-0.269135Ba
137Cs{syn.}30.07 ybeta-1.176137Ba
SI units & STP are used except where noted.
Caesium (Also spelled Cesium) is a chemical element in the periodic table that has the symbol Cs and atomic number 55. This is a soft silvery-gold Alkali metal which is one of the three metals that are liquid at room temperature. This element is most notably used in atomic clocks.

Caesium is sometimes spelt cesium, especially by Americans, but caesium is the official name preferred by IUPAC, although since 1993 it has recognized cesium as a variant.

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Notable Characteristics The electromagnetic spectrum of caesium has two bright lines in the blue part of the spectrum along with several other line in the red, yellow, and green. This metal is silvery gold in color and is both soft and ductile. Caesium is also the most electropositive and most alkaline chemical element and also has the least ionization potential of all the elements. Caesium is the least abundant of the five non-radioactive alkali metals. (Technically, francium is the least common alkali metal, but since it is highly radioactive with less than a gram in the entire earth at one time, its abundance can be considered zero in practical terms.)

Along with gallium and mercury, caesium is among the only metals that are liquid at room temperature. Caesium reacts explosively in cold water and also reacts with ice which is at temperatures above -116 Celsius. Caesium hydroxide (CsOH) is the strongest base known to exist and attacks glass. Applications Caesium is most notably used in atomic clocks, which are accurate to 5 seconds in 300 years.

More recently this metal has been used in ion propulsion systems. History Caesium (Latin caesius meaning "sky blue") was spectroscopically discovered by Robert Bunsen and Gustav Kirchhoff in 1860 in mineral water[?] from Durkheim[?]. Its identification was based upon the bright blue lines in its spectrum and it was the first element discovered by spectrum analysis. The first cesium metal was produced in 1881. Since 1967, the International System of Units (SI) has defined the second as 9,192,631,770 cycles of the radiation which corresponds to the transition between two energy levels of the ground state of the Caesium-133 atom. Historically, the most important use for cesium has been in research and development, primarily in chemical and electrical applications. Occurrence An alkali metal, caesium occurs in lepidolite, pollucte[?] (hydrated silicate of aluminium and caesium) and within other sources. One of the world's most significant and rich sources of this metal is located at Bernic Lake[?] in Manitoba. The deposits there are estimated to contain 300,000 tons of pollucite at an average of 20% caesium.

It can be isolated by electrolysis of fused cyanide and in a number of other ways. Exceptionally pure and gas-free caesium can be made by the thermal decomposition of caesium azide. The primary compounds of caesium are its chloride and its nitrate. The price of cesium in 1997 was about $US 30 per gram. Isotopes Caesium has 32 known istotopes which is more than any other element. The atomic masses of these isotopes range from 114 to 145. Even though this element has the largest number of isotopes, it only has one naturally occurring stable isotope, Cs-133. The radiogenic isotope Cs-137 has been used in hydrologic studies, analogous to the use of H-3. Cs-137 is produced from detonation of nuclear weapons and emissions from nuclear power plants. Beginning in 1954 with the commencement of nuclear testing, Cs-137 was released into the atmosphere where it is absorbed readily into solution. Once Cs-137 enters the ground water, it is deposited on soil surfaces and removed from the landscape primarily by particle transport[?]. As a result, the input function of these isotopes can be estimated as a function of time. Precautions Caesium is highly explosive in cold water. Caesium should be considered highly toxic. Some of its radioisotopes are even more toxic.

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