Natural krypton is a mixture of six stable isotopes : krypton-84 (56.99 percent), krypton-86 (17.28 percent), krypton-82 (11.59 percent), krypton-83 (11.5 percent), krypton-80 (2.29 percent), and krypton-78 (0.36 percent). Krypton has isotopes of every mass number from 69 through 101; of these isotopes,25 are radioactive and are produced by fission of uranium and by other nuclear reactions . The longest-lived of these, krypton-81 , has a half-life of 229,000 years. After it has been stored a few days, krypton obtained by nuclear fission contains only one radioactive isotope , krypton-85, which has a half-life of 10.7 years, because all the other radioactive isotopes have half-lives of 3 hours or less.
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When a current of electricity is passed through a glass tube containing krypton at low pressure , a bluish white light is emitted . The wavelength of an orange-red component of light emitted by stable krypton-86, because of its extreme sharpness, served from to as the international standard for the meter . (One meter equaled 1,650,763.73 times the wavelength of this line.)
Krypton is used in certain electric and fluorescent lamps and in a flashlamp employed in high-speed photography . Radioactive krypton-85 is useful for detecting leaks in sealed containers, with the escaping atoms detected by means of their radiation . Krypton is named from the Greek word kryptos, &#;hidden.&#;
Because its boiling point (&#;153.4 °C, or &#;244.1 °F) is about 30&#;40 °C (50&#;70 °F) higher than those of the major constituents of air, krypton is readily separated from liquid air by fractional distillation; it accumulates along with xenon in the least volatile portion. These two gases are further purified by adsorption onto silica gel , redistillation, and passage over hot titanium metal , which removes all impurities except other noble gases.
Krypton is the lightest of the noble gases that form isolable chemical compounds in macroscopic amounts. For many years it was considered to be totally unreactive. In the early s, however, krypton was found to react with the element fluorine when both are combined in an electrical-discharge tube at &#;183 °C (&#;297 °F); the compound formed is krypton difluoride, KrF2. Several other methods for the synthesis of KrF2 are now known, including irradiation of krypton and fluorine mixtures with ultraviolet radiation at &#;196 °C (&#;321 °F).
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SubscribeKrF2 is a colorless crystalline solid that is highly volatile and slowly decomposes at room temperature. No other molecular fluoride of krypton has been isolated, so all krypton compounds are derived from KrF2, where Kr is in the +2 oxidation state. Krypton difluoride is a powerful oxidative fluorinating agent. (Its oxidizing power means that it extracts electrons from other substances and confers on them a positive charge. Its fluorinating ability means that it transfers an F&#; ion to other substances. Hence, in a formal sense, oxidative fluorination is the net result of extraction of two electrons and addition of F&#;; this can be considered to be equivalent to the transfer of F+.) KrF2 is, for example, capable of oxidizing and fluorinating xenon to XeF6 and gold to AuF5.
The cationic species KrF+ and Kr2F3+ are formed in reactions of KrF2 with strong fluoride-ion acceptors such as the pentafluorides of Group 15, in which the fluoride ion F&#; is transferred to the pentafluoride to give complex salts that are analogous to those of XeF2; here no oxidation is involved. Among these complex salts are [KrF+][SbF6&#;] and [Kr2F3+][AsF6&#;]. The Kr2F3+ cation is V-shaped with a fluorine atom bonded to each of two krypton atoms and both krypton atoms bonded to a common fluorine in the middle, i.e., F(KrF)2+.
The KrF+ cation ranks among the most powerful chemical oxidizers presently known and is capable of oxidative fluorination of gaseous xenon to XeF5+ and chlorine, bromine, and iodine pentafluorides to the ClF6+, BrF6+, and IF6+ cations, respectively. The KrF+ cation behaves as only an oxidizing agent in converting gaseous oxygen to O2+.
The KrF+ cation has been shown to behave as a Lewis acid (electron-pair acceptor) toward a number of Lewis bases that are resistant to oxidation by the strongly oxidizing KrF+ cation at low temperatures. These Lewis acid-base adducts are exemplified by HCNKrF+ and F3CCNKrF+, which are formed as AsF6&#; salts. Such cations are the only known examples of krypton bonded to nitrogen. The compound Kr(OTeF5)2 is the only reported example of a compound in which krypton is bonded to oxygen. No compounds in which krypton is bonded to elements other than fluorine, oxygen, and nitrogen have been isolated.
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Clathrate &#;compounds,&#; in which the element is trapped in cagelike structures of water or other molecules, are known. There is no diatomic molecule of krypton.
Krypton is present in the air at about 1 ppm. The atmosphere of Mars contains a little (about 0.3 ppm) of krypton. It is characterised by its brilliant green and orange spectral lines. The spectral lines of krypton are easily produced and some are very sharp. In it was internationally agreed that the fundamental unit of length, the metre, should be defined as 1 m = 1,650,763.73 wavelengths (in vacuo) of the orange-red line of Kr-33.
Under normal conditions krypton is colourless, odourless, fairly expensive gas. Solid krypton is a white crystalline substance with a face-centered cubic structure which is common to all the "rare gases". Krypton difluoride, KrF2, has been prepared in gram quantities and can be made by several methods. Other compounds are unstable, unless isolated in a matrix at very low temperatures.
Applications
Krypton is used to fill electric lamp bulbs which are filled with a mixture of krypton and argon, and for various electronic devices. Krypton is also used in photographic projection lamps, in very high-powered electric arc lights used at airports and in some strobo-lamps, because it has an extremely fast respons to an electric current.
A mixture of stable and unstable isotopes of krypton is produced by slow neutron fission of uranium in nuclear reactors as Kripron-85, its most stable isotope. It is used to detect leaks in sealed containers, to excite phosphors in light sources with no external source of energy, and in medicine to detect abnormal heart openings.
Krypton in the environment
Krypton might be one of the rarest gases in the atmosphere, but in total there are more than 15 billion tonnes of this metal circulating in the planet, of which only about 8 tonnes a year are extracted, via liquid air.
Inhalation: This gas is inert and is classified as a simple asphyxiant. Inhalation in excessive concentrations can result in dizziness, nausea, vomiting, loss of consciousness, and death. Death may result from errors in judgment, confusion, or loss of consciousness which prevent self-rescue. At low oxygen concentrations, unconsciousness and death may occur in seconds without warning.
The effect of simple asphyxiant gases is proportional to the extent to which they diminish the amount (partial pressure) of oxygen in the air that is breathed. The oxygen may be diminished to 75% of it's normal percentage in air before appreciable symptoms develop. This in turn requires the presence of a simple asphyxiant in a concentration of 33% in the mixture of air and gas. When the simple asphyxiant reaches a concentration of 50%, marked symptoms can be produced. A concentration of 75% is fatal in a matter of minutes.
Symptoms: The first symptoms produced by a simple asphyxiant are rapid respirations and air hunger. Mental alertness is diminished and muscular coordination is impaired. Later judgment becomes faulty and all sensations are depressed. Emotional instability often results and fatigue occurs rapidly. As the asphyxia progresses, there may be nausea and vomiting, prostration and loss of consciousness, and finally convulsions, deep coma and death.
Krypton is a rare atmospheric gas and as such is non-toxic and chemically inert. The extreme cold temperature (-244oC) will freeze organisms on contact, but no long term ecological effects are anticipated.
Disposal considerations: When disposal becomes necessary, vent gas slowly to a well-ventilated out door location remote from personnel work areas and building air intakes. Do not dispose of any residual gas in compressed gas cylinders. Return cylinders to the supplier with residual pressure, the cylinder valve tightly closed. Please be advised that state and local requirements for waste disposal may be more restrictive or otherwise different from federal regulations. Consult state and local regulations regarding the proper disposal of this material.
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