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| General |
| Name, Symbol, Number | Caesium, Cs, 55 |
| Series | Alkali metals |
| Group, Period, Block | 1(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 level | 2, 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 |
| Miscellaneous |
| 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 |
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| 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.
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.
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.
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.
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.
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.
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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