Difference between revisions of "Caesium"

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{{infobox caesium}}
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{{Elementbox
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|name=caesium
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|number=55
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|symbol=Cs
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|left=[[Xenon|Xe]]
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|right=[[Barium|Ba]]
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|above=[[Rubidium|Rb]]
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|below=[[Francium|Fr]]
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|series=alkali metals
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|series comment=
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|group=1
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|period=6
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|block=s
 +
|series color=
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|phase color=
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|appearance=silvery gold
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|image name=Csmetal.jpg
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|image size=
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|image name 2=
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|image name 2 comment=
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|atomic mass=132.9054519
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|atomic mass 2=
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|atomic mass comment=
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|electron configuration=&#91;[[xenon|Xe]]&#93; 6s<sup>1</sup>
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|electrons per shell=2, 8, 18, 18, 8, 1
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|color=
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|phase=solid
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|phase comment=
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|density gplstp=
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|density gpcm3nrt=1.93
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|density gpcm3nrt 2=
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|density gpcm3mp=1.843
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|melting point K=301.59
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|melting point C=28.44
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|melting point F=83.19
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|melting point pressure=
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|boiling point K=944
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|boiling point C=671
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|boiling point F=1240
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|boiling point pressure=
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|triple point K=
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|triple point kPa=
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|critical point K=1938
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|critical point MPa=9.4
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|heat fusion=2.09
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|heat fusion 2=
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|heat fusion pressure=
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|heat vaporization=63.9
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|heat vaporization pressure=
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|heat capacity=32.210
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|heat capacity pressure=
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|vapor pressure 1=418
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|vapor pressure 10=469
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|vapor pressure 100=534
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|vapor pressure 1 k=623
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|vapor pressure 10 k=750
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|vapor pressure 100 k=940
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|vapor pressure comment=
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|crystal structure=[[body centered cubic]]
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|oxidation states=1
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|oxidation states comment=
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|electronegativity=0.79
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|number of ionization energies=3
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|1st ionization energy=375.7
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|2nd ionization energy=2234.3
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|3rd ionization energy=3400
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|atomic radius=265
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|atomic radius calculated=
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|covalent radius=244±11
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|Van der Waals radius=
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|magnetic ordering=[[paramagnetic]]<ref name=magnet>[http://www-d0.fnal.gov/hardware/cal/lvps_info/engineering/elementmagn.pdf Magnetic susceptibility of the elements and inorganic compounds], in Handbook of Chemistry and Physics 81th edition, CRC press. </ref>
 +
|electrical resistivity=
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|electrical resistivity at 0=
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|electrical resistivity at 20=205 n
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|thermal conductivity=35.9
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|thermal conductivity 2=
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|thermal diffusivity=
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|thermal expansion=
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|thermal expansion at 25=97
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|speed of sound=
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|speed of sound rod at 20=
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|speed of sound rod at r.t.=
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|Young's modulus=1.7
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|Shear modulus=
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|Bulk modulus=1.6
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|Poisson ratio=
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|Mohs hardness=0.2
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|Vickers hardness=
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|Brinell hardness=0.14
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|CAS number=7440-46-2
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|EC number=231-155-4
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|isotopes=
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{{Elementbox_isotopes_stable | mn=133 | sym=Cs | na=100% | n=78 }}
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{{Elementbox_isotopes_decay2 | mn=134 | sym=Cs
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| na=[[synthetic radioisotope|syn]] | hl=65.159 [[megasecond|Ms]]<br />(2.0648 [[years|y]])
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| dm1=[[electron capture|ε]] | de1=1.229 | pn1=134 | ps1=[[xenon|Xe]]
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| dm2=[[beta emission|β<sup>−</sup>]] | de2=2.059 | pn2=134 | ps2=[[barium|Ba]] }}
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{{Elementbox_isotopes_decay | mn=135 | sym=Cs
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| na=[[trace radioisotope|trace]] | hl=73 [[terasecond|Ts]]<br />(2.3 [[megayear|My]])
 +
| dm=[[beta emission|β<sup>−</sup>]] | de=0.269 | pn=135 | ps=[[barium|Ba]] }}
 +
{{Elementbox_isotopes_decay | mn=137 | sym=Cs
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| na=[[synthetic radioisotope|syn]] | hl=948.9 Ms<br />(30.07 y)
 +
| dm=[[beta emission|β<sup>−</sup>]] | de=1.176 | pn=137 | ps=[[barium|Ba]] }}
 +
|isotopes comment=
 +
}}
 
'''Caesium''' or '''cesium''' ({{pronEng|ˈsiːziəm}}) is the [[chemical element]] with the symbol '''Cs''' and [[atomic number]] 55. It is a soft, silvery-gold [[alkali metal]] with a melting point of {{nowrap|28 °C}} {{nowrap|(83 °F)}}, which makes it one of only [[liquid metal|five metals]] that are liquid at or near [[room temperature]].<ref>Along with [[rubidium]] ({{nowrap|39 °C}} {{nowrap|[102 °F]}}), [[francium]] ({{nowrap|27 °C}} {{nowrap|[81 °F]}}), [[mercury (element)|mercury]] ({{nowrap|−39 °C}} {{nowrap|[−38 °F]}}), and [[gallium]] ({{nowrap|30 °C}} {{nowrap|[86 °F]}}). <br>Bromine is also liquid at room temperature (-7.2 °C, 19 °F) but it is not a metal, but a [[halogen]].</ref>  Caesium is most notably used in [[atomic clock]]s.
 
'''Caesium''' or '''cesium''' ({{pronEng|ˈsiːziəm}}) is the [[chemical element]] with the symbol '''Cs''' and [[atomic number]] 55. It is a soft, silvery-gold [[alkali metal]] with a melting point of {{nowrap|28 °C}} {{nowrap|(83 °F)}}, which makes it one of only [[liquid metal|five metals]] that are liquid at or near [[room temperature]].<ref>Along with [[rubidium]] ({{nowrap|39 °C}} {{nowrap|[102 °F]}}), [[francium]] ({{nowrap|27 °C}} {{nowrap|[81 °F]}}), [[mercury (element)|mercury]] ({{nowrap|−39 °C}} {{nowrap|[−38 °F]}}), and [[gallium]] ({{nowrap|30 °C}} {{nowrap|[86 °F]}}). <br>Bromine is also liquid at room temperature (-7.2 °C, 19 °F) but it is not a metal, but a [[halogen]].</ref>  Caesium is most notably used in [[atomic clock]]s.
  

Latest revision as of 18:28, 15 August 2009

Xe ← caesium → Ba
Rb
↑
Cs
↓
Fr
Appearance
silvery gold
300px
General
Name, symbol, number caesium, Cs, 55
Element category alkali metals
Group, period, block 1, 6, s
Standard atomic weight 132.9054519 g/mol
Electron configuration [Xe] 6s1
Electrons per shell 2, 8, 18, 18, 8, 1 (Image)
Physical properties
Phase solid
Density (near r.t.) 1.93 g/cm3
Liquid density at m.p. 1.843 g/cm3
Melting point 301.59 K, 28.44 °C, 83.19 °F
Boiling point 944 K, 671 °C, 1240 °F
Critical point 1938 K, 9.4 MPa
Heat of fusion 2.09 kJ/mol1
Heat of vaporization 63.9 kJ/mol1
Specific heat capacity (25 °C) 32.210 J K−1 mol−1
Vapor 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
Electronegativity 0.79 (Pauling scale)
Ionization energies 1st: 375.7 kJ·mol−1
2nd: 2234.3 kJ·mol−1
3rd: 3400 kJ·mol−1
Atomic radius 265 pm
Covalent radius 244±11 pm
Miscellaneous
Crystal structure body centered cubic
Magnetic ordering paramagnetic[1]
Electrical resistivity (20 °C) 205 nΩ·m
Thermal conductivity (300 K) 35.9 W·m−1·K−1
Thermal expansion (25 °C) 97 µm·m−1·K−1
Young's modulus 1.7 GPa
Bulk modulus 1.6 GPa
Mohs hardness 0.2
Brinell hardness 0.14 MPa
CAS registry number 7440-46-2
EC number 231-155-4
Most stable isotopes
Main article: Isotopes of caesium
iso N.A. half-life DM DE (MeV) DP
133Cs 100% 133Cs is stable with 78 neutrons
134Cs syn 65.159 Ms
(2.0648 y) 		ε 1.229 134Xe
β− 2.059 134Ba
135Cs trace 73 Ts
(2.3 My) 		β− 0.269 135Ba
137Cs syn 948.9 Ms
(30.07 y) 		β− 1.176 137Ba
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Caesium or cesium (Template:PronEng) is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C (83 °F), which makes it one of only five metals that are liquid at or near room temperature.[2] Caesium is most notably used in atomic clocks.

Caesium is the international spelling standardized by the IUPAC, but in the United States it is more commonly spelled as cesium.[3]

Characteristics

High purity caesium metal.

The emission spectrum of caesium has two bright lines in the blue area of the spectrum along with several other lines in the red, yellow, and green areas. This metal is silvery gold in color and is both soft and ductile. Caesium has the lowest ionization potential of the chemical elements. Caesium is the least abundant of the five non-radioactive alkali metals. (Francium is the least common alkali metal but it has no stable isotopes.[4]).

Caesium, gallium, francium, rubidium, and mercury are the only pure metals liquid at or near room temperature. (Some sodium-potassium alloys are also liquid at room temperature.) Caesium reacts explosively in cold water and also reacts with ice at temperatures above −116 °C (−177 °F, 157 K).

Caesium hydroxide (CsOH) is a very strong base and will rapidly etch the surface of glass. CsOH is often stated to be the "strongest base", but in fact many compounds such as n-butyllithium and sodium amide are stronger but are not classic hydroxide bases and are destroyed by water.

Applications

Probably the most widespread use of caesium today is in caesium formate-based drilling fluids for the oil industry. The high density of the caesium formate brine (up to 2.3 sg), coupled with the relatively benign nature of natural caesium (which has minimal radioactivity because it is almost entirely composed of a stable istotope), reduces the requirement for toxic high-density suspended solids in the drilling fluid, which is a significant technological, engineering and environmental advantage.[5][6]

Caesium is also used in atomic clocks, which are accurate to seconds over many thousands of years. Since 1967, the International System of Measurements has based its unit of time, the second, on the properties of caesium. The International System of Units (SI) defines the second as 9,192,631,770 cycles of the radiation, which corresponds to the transition between two hyperfine energy levels of the ground state of the 133Cs atom.

History

Caesium (Latin caesius meaning "blueish grey")[9][10] was spectroscopically discovered by Robert Bunsen and Gustav Kirchhoff in 1860 in mineral water from Dürkheim, Germany. The residues of 44,000 liters of mineral water yielded several grams of caesium salt for further analysis. Its identification was based upon the bright blue lines in its spectrum and it was the first element discovered by spectrum analysis.[11] The first caesium metal was produced in 1882 by electrolysis of caesium chloride by Carl Setterberg. Setterberg received his PhD from Kekule and Bunsen for this work. Historically, the most important use for caesium has been in research and development, primarily in chemical and electrical applications.

Occurrence

Pollucite, a caesium mineral.

An alkali metal, caesium occurs in lepidolite, pollucite (hydrated silicate of aluminium and caesium) and within other sources. One of the world's most significant and rich sources of this metal is at Bernic Lake in Manitoba. The deposits there are estimated to contain 300,000 metric tons of pollucite ore at an average of composition of 20% caesium by weight.

It can be isolated by electrolysis of fused caesium 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 caesium chloride and its nitrate. The price of caesium metal in 1997 was about US$30 per gram, but its compounds are much cheaper.

See also: category:Caesium minerals

Isotopes

Main article: Isotopes of caesium

Caesium has at least 39 known isotopes, which is more than any other element except francium. The atomic masses of these isotopes range from 112 to 151. Even though this element has a large number of isotopes, it has only one naturally occurring stable isotope, 133Cs. Most of the other isotopes have half-lives from a few days to fractions of a second. The radiogenic isotope 137Cs has been used in hydrologic studies, analogous to the use of 3H. 137Cs is produced from the detonation of nuclear weapons and is produced in nuclear power plants, and was released to the atmosphere most notably from the 1986 Chernobyl meltdown. This isotope (137Cs) is one of the numerous products of fission, directly issued from the fission of uranium.

High purity caesium-133 (preserved under argon)

Beginning in 1945 with the commencement of nuclear weapons testing, 137Cs was released into the atmosphere where it is not absorbed readily into solution and is returned to the surface of the earth as a component of radioactive fallout. Once 137Cs 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 cannot be estimated as a function of time. Caesium-137 has a half-life of 30.17 years. It decomposes to barium-137m (a short-lived product of decay) then to a form of nonradioactive barium.

Precautions

All alkali metals are highly reactive. Caesium, being one of the heavier alkali metals, is also one of the most reactive and is highly explosive when it comes in contact with water. The hydrogen gas produced by the reaction is heated by the thermal energy released at the same time, causing ignition and a violent explosion (the same as all alkali metals) - but caesium is so reactive that this explosive reaction can even be triggered by cold water or ice.

Caesium is highly pyrophoric and ignites spontaneously in air to form caesium hydroxide and various oxides. Caesium hydroxide is an extremely strong base, and can etch glass.

Caesium compounds are rarely encountered by most persons. All caesium compounds should be regarded as mildly toxic because of its chemical similarity to potassium. Large amounts cause hyperirritability and spasms, but such amounts would not ordinarily be encountered in natural sources, so Cs is not a major chemical environmental pollutant. Rats fed caesium in place of potassium in their diet die,[ref. needed] so this element cannot replace potassium in function in rats.

The isotopes 134Cs and 137Cs (present in the biosphere in small amounts as a result of radiation leaks) represent a radioactivity burden which varies depending on location. Radiocaesium does not accumulate in the body as effectively as many other fission products (such as radioiodine and radiostrontium), which are actively accumulated by the body; as with other alkali metals, it washes out of the body relatively quickly in the sweat and urine, unlike strontium which accumulates in the bone.[ref. needed]

See also

References

Wikisource has the text of the 1911 Encyclopædia Britannica article Caesium.
  1. ↑ Magnetic susceptibility of the elements and inorganic compounds, in Handbook of Chemistry and Physics 81th edition, CRC press.
  2. ↑ Along with rubidium (39 °C [102 °F]), francium (27 °C [81 °F]), mercury (−39 °C [−38 °F]), and gallium (30 °C [86 °F]).
    Bromine is also liquid at room temperature (-7.2 °C, 19 °F) but it is not a metal, but a halogen.
  3. ↑ IUPAC Periodic Table of the Elements
  4. ↑ Adloff, Jean-Pierre; George B. Kauffman (09/23 2005). "Francium (Atomic Number 87), the Last Discovered Natural Element". The Chemical Educator 10 (5). doi:10.1333/s00897050956a. Retrieved on 2006-05-16. 
  5. ↑ Drilling and Completing Difficult HP/HT Wells With the Aid of Cesium Formate Brines-A Performance Review
  6. ↑ Overview: Cesium Formate Fluids
  7. ↑ United States Patent 6230628: Infrared illumination compositions and articles containing the same
  8. ↑ LUU-19 Flare
  9. ↑ Bunsen quotes Aulus Gellius Noctes Atticae II, 26 by Nigidius Figulus: Nostris autem veteribus caesia dicts est quae Graecis, ut Nigidus ait, de colore coeli quasi coelia.
  10. ↑ Oxford English Dictionary, 2nd Edition
  11. ↑ G. Kirchhoff, R. Bunsen (1861). "Chemische Analyse durch Spectralbeobachtungen". Annalen der Physik und Chemie 189 (7): 337–381. doi:10.1002/andp.18611890702. 

External links

Commons logo.png Public domain and freely licensed images and media can be found in the corresponding category on Wikimedia Commons.


Template:Alkalimetals

 
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