|
Krypton (Kr)
| 36 |
bromine ← krypton → rubidium |
Ar
↑
Kr
↓
Xe |
|
Periodic Table - Extended Periodic
Table | | |
| General |
| Name, Symbol, Number |
krypton, Kr, 36 |
| Chemical series |
noble gases |
| Group, Period, Block |
18, 4, p |
| Appearance |
colorless
 |
| Standard atomic weight |
83.798(2) g·mol−1 |
| Electron configuration |
[Ar] 3d10 4s2
4p6 |
| Electrons per shell |
2, 8, 18, 8 |
| Physical
properties |
| Phase |
gas |
| Density |
(0 °C, 101.325 kPa)
3.749 g/L |
| Melting point |
115.79 K
(-157.36 °C, -251.25 °F) |
| Boiling point |
119.93 K
(-153.22 °C, -244.12 °F) |
| Triple point |
115.775 K, 73.2 kPa[1] |
| Critical point |
209.41 K, 5.50 MPa |
| Heat of fusion |
1.64 kJ·mol−1 |
| Heat of vaporization |
9.08 kJ·mol−1 |
| Heat capacity |
(25 °C) 20.786
J·mol−1·K−1 |
Vapor pressure
| P(Pa) |
1 |
10 |
100 |
1 k |
10 k |
100 k |
| at T(K) |
59 |
65 |
74 |
84 |
99 |
120 | |
| Atomic
properties |
| Crystal structure |
cubic face centered |
| Oxidation states |
2 |
| Electronegativity |
3.00 (scale Pauling) |
Ionization
energies
(more) |
1st: 1350.8 kJ·mol−1 |
| 2nd: 2350.4 kJ·mol−1 |
| 3rd: 3565 kJ·mol−1 |
| Atomic radius (calc.) |
88 pm |
| Covalent radius |
110 pm |
| Van der Waals radius |
202 pm |
| Miscellaneous |
| Magnetic ordering |
nonmagnetic |
| Thermal conductivity |
(300 K)
9.43x10-3 W·m−1·K−1 |
| Speed of sound |
(gas, 23 °C) 220 m/s |
| Speed of sound |
(liquid) 1120 m/s |
| CAS registry number |
7439-90-9 |
| Selected
isotopes |
Main article: Isotopes of krypton
| iso |
NA |
half-life |
DM |
DE (MeV) |
DP |
| 78Kr |
0.35% |
2.3×1020 y |
ε ε |
- |
78Se |
| 79Kr |
syn |
35.04 h |
ε |
- |
79Br |
| β+ |
0.604 |
79Br |
| γ |
0.26, 0.39, 0.60 |
- |
| 80Kr |
2.25% |
Kr is stable with 44 neutrons |
| 81Kr |
syn |
2.29×105 y |
ε |
- |
81Br |
| γ |
0.281 |
- |
| 82Kr |
11.6% |
Kr is stable with 46 neutrons |
| 83Kr |
11.5% |
Kr is stable with 47 neutrons |
| 84Kr |
57% |
Kr is stable with 48 neutrons |
| 85Kr |
syn |
10.756 y |
β- |
0.687 |
85Rb |
| 86Kr |
17.3% |
Kr is stable with 50
neutrons | |
|
Krypton is a chemical element with
the symbol Kr and atomic number 36. A colorless, odorless, tasteless
noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by
fractionally distilling liquified air, and is often used with other rare gases
in fluorescent lamps. Krypton is inert for most practical purposes but it is
known to form compounds with fluorine. Krypton can also form clathrates with
water when atoms of it are trapped in a lattice of the water
molecules.
From 1960 to 1983, the distance of the meter was
defined in terms of the orange-red spectral line of krypton-86, an isotope of
krypton. It as well as all other noble gases can be used in lighting and
photography. Krypton has an important role in production and usage of the
krypton fluoride laser.
Physical
properties
Krypton is characterized by a brilliant green and
orange spectral signature. It is one of the products of uranium fission.
Solidified krypton is white and crystalline with a face-centered cubic crystal
structure which is a common property of all noble gases.
History
Krypton (Greek κρυπτόν, krypton meaning "hidden thing" or
"hidden one") was discovered in Great Britain in 1898 by Sir William Ramsay and
Morris Travers in residue left from evaporating nearly all components of liquid
air. William Ramsay was awarded the 1904 Nobel Prize in Chemistry for discovery
of a series of noble gases including krypton.
Metic
Role
In 1960 an international agreement defined the meter in terms of wavelength
of light emitted by the krypton-86 isotope. This agreement replaced the
longstanding standard meter located in Paris which was a metal bar made of a
platinum-iridium alloy (the bar was originally estimated to be one ten millionth
of a quadrant of the earth's polar circumference). But 23 years later the
krypton-based standard was replaced itself by a definition based on the speed of
light — a fundamental physical constant. In October 1983 the Bureau
International des Poids et Mesures (International Bureau of Weights and
Measures) defined the metre as the distance that light travels in a vacuum
during 1/299,792,458 s.
Occurence
The concentration of krypton in earth's atmosphere is about 1 ppm. It can be
extracted from liquid air by fractional distillation. The amount of
krypton in space is uncertain as is the amount is derived from the meteoritic
activity and that from solar winds. The first measurements suggest an
overabundance of krypton in space.
Compounds
Like the other noble gases, krypton is chemically inert. However, following
the first successful synthesis of xenon compounds in 1962, synthesis of krypton
difluoride was reported in 1963. Other fluorides and a salt of a krypton oxoacid
have also been found. ArKr+ and KrH+ molecule-ions have been investigated and
there is evidence for KrXe or KrXe+.
At the University of Helsinki in Finland, HKrCN and HKrCCH (krypton
hydride-cyanide and hydrokryptoacetylene) were synthesized and determined to be
stable up to 40K (M. Räsänen et al.).
Isotopes
There are 31 known isotopes of Krypton (Kr). Naturally
occurring krypton is made of five stable and one slightly radioactive isotope.
Its spectral signature can be produced with some very sharp lines.
81Kr, the product of atmospheric reactions is produced with the other
naturally occurring isotopes of krypton. Being radioactive it has a half-life of
250,000 years. Krypton is highly volatile when it is near surface waters and
81Kr has been used for dating old (50,000 - 800,000 year)
groundwater.
85Kr is an inert radioactive noble gas with a half-life of 10.76
years. It is produced by fission of uranium and plutonium. It is produced by
nuclear bomb testing and nuclear reactors. 85Kr is released during
the reprocessing of fuel rods from nuclear reactors. Concentrations at the North
Pole are 30% higher than at the South Pole as most nuclear reactors are in the
northern hemisphere.
Standard atomic mass: 83.798(2) u
Table
nuclide
symbol |
Z(p) |
N(n) |
isotopic mass (u)
|
half-life |
nuclear
spin |
representative
isotopic
composition
(mole
fraction) |
range of natural
variation
(mole
fraction) |
| excitation energy |
| 69Kr |
36 |
33 |
68.96518(43)# |
32(10) ms |
5/2-# |
|
|
| 70Kr |
36 |
34 |
69.95526(41)# |
52(17) ms |
0+ |
|
|
| 71Kr |
36 |
35 |
70.94963(70) |
100(3) ms |
(5/2)- |
|
|
| 72Kr |
36 |
36 |
71.942092(9) |
17.16(18) s |
0+ |
|
|
| 73Kr |
36 |
37 |
72.939289(7) |
28.6(6) s |
3/2- |
|
|
| 73mKr |
433.66(12)
keV |
107(10) ns |
(9/2+) |
|
|
| 74Kr |
36 |
38 |
73.9330844(22) |
11.50(11) min |
0+ |
|
|
| 75Kr |
36 |
39 |
74.930946(9) |
4.29(17) min |
5/2+ |
|
|
| 76Kr |
36 |
40 |
75.925910(4) |
14.8(1) h |
0+ |
|
|
| 77Kr |
36 |
41 |
76.9246700(21) |
74.4(6) min |
5/2+ |
|
|
| 78Kr |
36 |
42 |
77.9203648(12) |
STABLE [>1.1E+20 a] |
0+ |
0.00355(3) |
|
| 79Kr |
36 |
43 |
78.920082(4) |
35.04(10) h |
1/2- |
|
|
| 79mKr |
129.77(5)
keV |
50(3) s |
7/2+ |
|
|
| 80Kr |
36 |
44 |
79.9163790(16) |
STABLE |
0+ |
0.02286(10) |
|
| 81Kr |
36 |
45 |
80.9165920(21) |
2.29(11)E+5 a |
7/2+ |
|
|
| 81mKr |
190.62(4)
keV |
13.10(3) s |
1/2- |
|
|
| 82Kr |
36 |
46 |
81.9134836(19) |
STABLE |
0+ |
0.11593(31) |
|
| 83Kr |
36 |
47 |
82.914136(3) |
STABLE |
9/2+ |
0.11500(19) |
|
| 83m1Kr |
9.4053(8)
keV |
154.4(11) ns |
7/2+ |
|
|
| 83m2Kr |
41.5569(10)
keV |
1.83(2) h |
1/2- |
|
|
| 84Kr |
36 |
48 |
83.911507(3) |
STABLE |
0+ |
0.56987(15) |
|
| 84mKr |
3236.02(18)
keV |
1.89(4) µs |
8+ |
|
|
| 85Kr |
36 |
49 |
84.9125273(21) |
10.776(3) a |
9/2+ |
|
|
| 85m1Kr |
304.871(20)
keV |
4.480(8) h |
1/2- |
|
|
| 85m2Kr |
1991.8(13)
keV |
1.6(7) µs [1.2(+10-4) µs] |
(17/2+) |
|
|
| 86Kr |
36 |
50 |
85.91061073(11) |
STABLE |
0+ |
0.17279(41) |
|
| 87Kr |
36 |
51 |
86.91335486(29) |
76.3(5) min |
5/2+ |
|
|
| 88Kr |
36 |
52 |
87.914447(14) |
2.84(3) h |
0+ |
|
|
| 89Kr |
36 |
53 |
88.91763(6) |
3.15(4) min |
3/2(+#) |
|
|
| 90Kr |
36 |
54 |
89.919517(20) |
32.32(9) s |
0+ |
|
|
| 91Kr |
36 |
55 |
90.92345(6) |
8.57(4) s |
5/2(+) |
|
|
| 92Kr |
36 |
56 |
91.926156(13) |
1.840(8) s |
0+ |
|
|
| 93Kr |
36 |
57 |
92.93127(11) |
1.286(10) s |
1/2+ |
|
|
| 94Kr |
36 |
58 |
93.93436(32)# |
210(4) ms |
0+ |
|
|
| 95Kr |
36 |
59 |
94.93984(43)# |
114(3) ms |
1/2(+) |
|
|
| 96Kr |
36 |
60 |
95.94307(54)# |
80(7) ms |
0+ |
|
|
| 97Kr |
36 |
61 |
96.94856(54)# |
63(4) ms |
3/2+# |
|
|
| 98Kr |
36 |
62 |
97.95191(64)# |
46(8) ms |
0+ |
|
|
| 99Kr |
36 |
63 |
98.95760(64)# |
40(11) ms |
(3/2+)# |
|
|
| 100Kr |
36 |
64 |
99.96114(54)# |
10# ms [>300 ns] |
0+ |
|
|
Krypton's multiple emission lines make ionized
krypton gas discharges appear white, which in turn makes krypton-based bulbs
useful in photography as a brilliant white light source. Krypton is thus used in
some types of photographic flashes used in high speed photography. Fluorescent light bulbs
are filled with a mixture of krypton and argon gases. Krypton gas is also
combined with other gases to make luminous signs that glow with a bright
greenish-yellow light.
Krypton's white discharge is often used to
good effect in colored gas discharge tubes, which are then simply painted or
stained in other ways to allow the desired color (for example, "neon" type
advertising signs where the letters appear in differing colors, are often
entirely krypton-based). Krypton is also capable of much higher light power
density than neon in the red spectral line region, and for this reason, red
lasers for high power laser light shows are krypton lasers with mirrors which
select out the red spectral line for laser amplification and emission, rather
than the more familiar helium-neon variety, which could never practically
achieve the multi-watt red laser light outputs needed for this
application.
Krypton has an important role in production and
usage of the krypton fluoride
laser. The laser has been important in the
nuclear fusion energy research community in confinement experiments. The
laser has
high beam uniformity, short wavelength, and the ability to
modify the spot size to track an imploding pellet.
In experimental particle physics, liquid krypton is
used to construct quasi-homogenious electromagnetic calorimeters. A notable example is the
calorimeter of the NA48 experiment at CERN containing about 27 tons of liquid
krypton. This usage is rare, since the cheaper liquid argon is typically used. The advantage
of krypton over agron is a small Molière
radius of 4.7cm, which allows for excellent
spatial resolution and low degree of overlapping. The other parameters relevant
for calorimetry application are: radiation
length of X0 = 4.7cm, density of
2.4g/cm³.
By: Zookeeper - 2007-12-01 01:07:23
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