Noble gas

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Noble gas refers to periodic table of ele ments The gas elementary substance corresponding to all the elements of Group 0 on, also known as inert gas 。 At normal temperature and pressure, they are colorless and tasteless monatomic gases, which are difficult to carry out chemical reactions. There are 7 kinds of rare gases. They are helium （He）、 neon （Ne）、 argon （Ar）、 Krypton （Kr）、 Xenon （Xe）、 Radon gas (Rn, radioactive) 鿫 (Og, radioactive, artificial element). Among them, Og is a rare gas synthesized artificially. The atomic nucleus is very unstable, and the half-life is very short, only 5 milliseconds.^[1-2]

Chinese name: Noble gas
Foreign name: noble gases
Alias: inert gas 、 Noble gas
Water solubility: Insoluble in water

Appearance: Colorless and odorless gas
Application: Rechargeable bulb, as protective gas, etc
Include: helium ， neon ， argon ， Krypton ， Xenon ， Radon gas ， Og
Quantity: 7 found
family: 0 Family

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Since "noble gasses" was discovered by chemists in the 19th century, its name has been changed many times due to deep understanding of its nature. Originally they were called rare gases, because chemists thought they were very rare. However, this statement only applies to some of these elements, not all of which are rare. For example, the content of argon (Ar, argon) in the earth's atmosphere accounts for 0.923%, more than carbon dioxide （0.03%）； The content of helium in the earth's atmosphere is really small, but it is quite abundant in the universe, accounting for 23%, second only to hydrogen (75%). Therefore, chemists also call them inert gases (also called inert gases), which means that their reactivity is very low and no compounds have ever appeared in nature. For those scientists who need to use compounds to find elements in the early stage, these elements are relatively difficult to find. However, recent research indicates that they can combine with other elements to form compounds (i.e rare gas compound ）, but only by means of artificial synthesis. So it was finally renamed noble gases (also known as noble gases, noble gases or noble gases), which was translated from German by Edelgas and was named by Hugo Edelman in 1898. "Noble" is similar to "precious metals" such as gold, which means that they are not prone to chemical reactions, but not unable to produce any compounds.

In terms of Chinese translation, the three places on both sides of the Taiwan Straits have different titles. In the Chemical Nomenclature published by the National Commission for the Examination and Approval of Natural Science Terms on the Chinese mainland in 1991, it was officially stipulated that "noble gases" should be referred to as noble gases. In the Common English and Chinese Vocabulary of Secondary Education, the Hong Kong Education Bureau called "noble gasses" (high) expensive gases, while the general society still calls them inert gases. In Taiwan, the National Institute of Education of the National Compilation and Translation Museum suggested that "noble gases" should be often referred to as inert gases, rather than inert gases and rare gases. However, some are also called noble gases.^[3]

Discovery history

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In 1868, astronomers found a special yellow spectral line D3 in the spectrum of the sun, which is different from the two yellow spectral lines D1 and D2 of sodium already known, thus predicting that there may be an unknown element in the sun. Later, this element was named "helium", meaning "solar element"^[4] 。

Rare gas luminescence

More than 20 years later, Ramsey confirmed that helium also exists on the earth. In 1895, American geologist Hilbrandt observed that heating uranium yttrium ore in sulfuric acid would produce a gas that could neither spontaneously ignite nor support combustion. He thought that this gas might be nitrogen or argon, but did not continue to study. After Ramsey knew this experiment, he repeated it with uraninite to get a small amount of gas. In use Spectral analysis When testing the gas, I thought I could see the spectrum of argon, but unexpectedly I found a yellow line and several weak bright lines of other colors. Ramsey compares it with known spectral lines, and none is similar to it. After hard thinking, I finally remembered the helium found on the sun 27 years ago. The spectrum of helium is just the yellow line. If the two yellow lines can coincide, then the gas emitted from uraninite should be the solar element helium. Ramsey was very cautious, and asked the most famous British spectroscopic expert Crookes to help test and confirm that the unknown gas obtained by Ramsey was the "solar element" gas. In March 1895, Ramsey first published a brief report on the discovery of helium on the earth in Chemical News, and officially announced the discovery at the annual meeting of British chemistry in the same year. Later, helium was found in the atmosphere, water, natural gas, petroleum gas, uranium and other ores, even in meteorites.

In 1902, Dmitry Mendeleev accepted the discovery of helium and argon, and these rare gases were included in his element list, which was classified as group 0, while periodic table of ele ments That is, it evolved from this arrangement^[5] 。

Ramsey continued to use fractionation to separate liquid air into different components to find other noble gases. He discovered three new elements in 1898: krypton, neon and xenon. "Krypton" comes from the Greek "κ ρνπτ (krupt ó s)", which means "hiding"; "Ne" originates from the Greek "ν o (n é os)", meaning "new"; "Xenon" originates from the Greek "ξν o (x é nos)", which means "stranger".

Radon gas was discovered by Friedrich Ernst Dang in 1898. It was originally named radium radiation, but it was not listed as a rare gas at that time^[6] 。 It was not until 1904 that it was found that its characteristics were similar to those of other rare gases. In 1904, Rayleigh and Ramsey won the Nobel Prize in Physics and Chemistry respectively, in recognition of their discovery in the field of rare gases^[7] 。 Sid Blom, president of the Royal Swedish Academy of Sciences, said in a speech: "Even if the predecessors failed to identify any element in this family, a new element family can still be found, which is unique in the history of chemistry and has a special significance for the development of science in essence.^[7] ”

The discovery of rare gases contributes to the development of general understanding of atomic structure. In 1895, French chemist Henri Moissan The reaction between fluorine (the element with the highest electronegativity) and argon (rare gas) was attempted, but failed. Until the end of the 20th century, scientists were still unable to prepare argon compounds, but these attempts helped to develop new atomic structure theories. From these experimental results, the Danish physicist Niels Bohr In 1913, it was proposed that the electrons in the atom are arranged around the nucleus in the form of an electronic layer. The outermost electronic layer of all rare gas elements except helium always contains 8 electrons. In 1916, Gilbert Newton Lewis Developed Octet Rule It is pointed out that there are 8 electrons on the outermost electron layer, which is the most stable arrangement of any atom. This electron arrangement makes them not react with other elements, because they do not need more electrons to fill their outermost electron layer.

But in 1962, Neil Bartlett discovered the first noble gas compound Xenon hexafluoroplatinum 。 Other noble gas compounds were subsequently discovered: radon compounds were discovered in 1962 Radon difluoride ； And discovered krypton in 1963 Krypton difluoride 。 In 2000, the first stable argon compound Hydrogen fluoride argon (HARF) was successfully prepared at 40K (- 233.2 ℃).^[8]

In December 1998, scientists from the Joint Nuclear Research Institute in Dubna, Russia, bombarded plutonium with calcium atoms to produce a single atom of element 114, which was later named Fl. Preliminary chemical experiments have shown that this element may be the first super heavy element. Although it is located in the 14th group of the periodic table, it has noble gas characteristics. In October 2006, scientists from the Joint Nuclear Research Institute and Lawrence Livermore National Laboratory of the United States successfully synthesized Og by bombarding californium with calcium atoms, which is the seventh element of Group 0^[9] 。

Mike Barlow, a professor at University College London, UK, and his colleagues used the Herschel Space Telescope of the European Space Agency to observe the Crab Nebula 6500 light-years away from the Earth in the far infrared band, and found argon and hydrogen molecules. What they observed was the argon isotope Ar-36. The energy from the neutron star in the center of the Crab Nebula ionized it, and then formed argon and hydrogen molecules with hydrogen. This discovery also supports the theory that Ar-36 isotope originated from the center of supernova.

About a hundred years after the discovery of nitrogen, British chemist Rayleigh, J.W.S.1842-1919）， On the one hand, oxygen, carbon dioxide and water vapor are removed from the air to obtain nitrogen; On the other hand, nitrogen is obtained from the decomposition of nitrogen compounds. He compared the two kinds of nitrogen from different sources and found that under normal conditions, the density of the former is 1.2572g/l, and the density of the latter is 1.2508g/l. Why is the density of nitrogen in the air higher? Is there any heavy inert gas in it? The British chemist Ramsay (W.1852-1916) used burning magnesium to interact with nitrogen in the air to remove nitrogen in the air, leaving a small amount of rare gas. It is proved by spectral test that it is a new gas element called argon. In the next few years, he separated three other rare gases from crude argon -- neon, krypton and xenon -- by fractional distillation. In 1895, Lemsey treated the asphalt oil mine with sulfuric acid to produce a gas, which was identified as helium by spectrum. He won the Nobel Prize in Chemistry in 1904 for his discovery of helium, neon, krypton, argon and xenon.

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In atoms of inert gas elements, the arrangement of electrons in each electron layer is just a stable number. Therefore, it is not easy for atoms to lose or get electrons, and it is difficult for atoms to react with other substances. Therefore, these elements are called "inert gas elements".

In inert gas atoms with larger atomic weight and more electrons, the outermost electrons are far away from the atomic nucleus, and the binding is relatively weak. If we encounter other atoms with strong electron attraction, these outermost electrons will be lost, and a chemical reaction will take place.

Rare gas element compounds

In 1933, a famous American chemist Pauline (L. Pauling) predicted that by calculating the ion radius Xenon hexafluoride （XeF six ）KrF six ）、 Xenonic acid And its salts. Inspired by the first report of Aintopov and Pauling's prediction, D.M. Younst tried to synthesize Xenon fluoride And xenon chloride were unsuccessful. In the experiment of xenon fluoride synthesis by discharge method, he mixed fluorine and xenon in a certain proportion, applied 30000 V voltage between copper electrodes to conduct spark discharge, but failed to detect the formation of xenon fluoride. Regrettably, in 1961, Pauling also denied his original prediction, thinking that "xenon is completely chemically nonreactive, and it can not generate compounds that usually contain covalent bonds or ionic bonds".

The development of history was quite dramatic. In 1962, the Canadian chemist N. Bartlett first synthesized xenon and fluorine compounds in the second year when Pauling denied his prediction. Since 1960, several new fluorides of platinum group metals have been reported in the literature, which are strong oxidants, including fluorides of high valence platinum platinum hexafluoride （PtF six ）Is even more oxidizing than fluorine. Bartlett first used PtF six Mixed with equimolar oxygen at room temperature, a dark red solid was obtained. The chemical formula of this compound was confirmed as O by X-ray diffraction analysis and other experiments two PtF six , the reaction equation is: O two +PtF six →O two PtF six 。 Bartlett is smart and good at association, analogy and reasoning. He considered O two Of First ionization energy It is 1175.7kJ/mol. The first ionization energy of xenon is 1175.5kJ/mol, which is slightly lower than the first ionization energy of oxygen molecule. Since O two Can be used by PtF six Oxidation, xenon should also be able to be oxidized by PtF six Oxidation. He also calculated Lattice energy , if XePtF is generated six , whose lattice energy is only less than O two PtF six Small 41.84kJ/mol. This indicates that XePtF six Once generated, it should also be stable. So Bartlett synthesized O according to the above inference two PtF six The PtF six It is surprisingly easy to obtain an orange solid XePtF at room temperature by mixing the vapor of six ：Xe+PtF six →XePtF six

The first noble gas compound—— Xenon hexafluoroplatinum （XePtF six ）Miraculously appeared, and shocked the entire chemical world with its unique experience and demeanor, marking the establishment of noble gas chemistry and opening up a new field of noble gas chemistry research. The compound is stable at room temperature and its vapor pressure is very low. It is insoluble in non-polar solvents carbon tetrachloride , which means it may be Ionic compound 。 It can sublimate when heated in vacuum, hydrolyze rapidly when meeting water, and escape gas: 2XePtF six +6H two O→2Xe↑+O two ↑+2PtO two +12HF

In June 1962, Bartlett published an important short article in the British journal Proceedings of the Chemical Society, officially announcing his experimental report to the chemical community, which shocked the entire chemical community. In August of the same year, H.H. Classen directly obtained XeF when mixing xenon and fluorine at a volume ratio of 1:5 under heating and pressure four And produced XeF at the end of the year two And XeF six 。 The success of direct synthesis of xenon fluoride has further stimulated chemists' enthusiasm for the synthesis of noble gas compounds. In a short period of time after that, a series of xenon fluoride compounds, xenon fluoride oxides, xenon oxylate, etc. with different valence states were successively synthesized, and their physical and chemical properties, molecular structure, and chemical bond nature were extensively studied and discussed, thus greatly enriching and broadening the research field of rare gas chemistry.

By the beginning of 1963, some compounds related to krypton and radon had also been synthesized. The smaller the atom, the stronger the constraint on the electron and the stronger the "inertia" of the element, so it is more difficult to synthesize compounds of helium, neon and argon. Scientists from the University of Helsinki in Finland reported in the British journal Nature published on the 24th that they had synthesized stable compounds of the inert gas element argon for the first time—— Hydrogen fluoride argon , the molecular formula is HarF. It is a solid stable substance at low temperature, and will decompose into argon and hydrogen fluoride when heated. Scientists believe that using this new technology, it is also expected to produce stable compounds of helium and neon respectively.

On February 6, 2017, the team of Wang Huitian and Zhou Xiangfeng from Nankai University of China and their collaborators published a paper on the synthesis of helium sodium compound Na ₂ He under high pressure in Nature Chemistry, ending the history of helium free compounds, which marks that China has moved to the forefront in the field of rare gas chemistry.^[12]

Physical and chemical properties

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The air contains about 0.94% (volume percent) of noble gases, most of which are argon 。

Noble gases are colorless, odorless and tasteless, slightly soluble in water, and their solubility increases with the increase of molecular weight. The molecules of rare gases are all composed of single atoms, and their melting points and boiling points are very low. With the increase of atomic weight, the melting points and boiling points increase. They can be liquefied at low temperatures.

Noble gas under high voltage electric field

The outermost electronic structure of noble gas atoms is n s two n p six (1s for helium two ）They are the most stable structures. Their characteristics can be explained by modern atomic structure theory: they all have stable eight electron configurations. Their outermost electron layer is "full" (i.e Octet State), so they are very stable and rarely undergo chemical reaction. So far, only hundreds of them have been successfully prepared rare gas compound 。 The melting point and boiling point of each noble gas are very close, and the temperature difference is less than 10 ° C (18 ° F), so they only exist as liquid in a very small temperature range. The electron affinity of noble gases is close to zero. Compared with other elements, they have high Ionization potential 。 Therefore, the noble gas atoms in the General conditions It is not easy to get or lose electrons Chemical bond 。 It is not only difficult to combine with other elements, but also has low chemical activity Monatomic molecule There are only weak Van der Waals (Mainly Dispersion force ）。

Through gas liquefaction and fractionation, neon, argon, krypton and xenon can be obtained from the air, while helium is usually extracted from natural gas, and radon is usually extracted from radium compounds through radioactivity To separate after decay. Rare gases are mainly used in lighting equipment, welding and space exploration in industry. Helium will also be used in deep-sea diving. If the diving depth is more than 55 meters, the nitrogen in the compressed air bottle used by divers should be replaced by helium to avoid signs of oxygen poisoning and nitrogen anesthesia. On the other hand, due to hydrogen It is very unstable, easy to burn and explode. Today's airships and balloons use helium instead of hydrogen.

The basic properties of noble gas elements are listed in the table below.

nature	He	Ne	Ar	Kr	Xe	Rn
colour	colourless	colourless	colourless	colourless	colourless	colourless
Spectral color (in discharge tube)	pink	red	Bluish violet	Blue-green	Bright white	-
Gas density (g/L)	zero point one seven eight five	zero point nine zero zero two	one point seven eight zero nine	three point seven zero eight	five point eight five one	nine point seven three
Melting point (K)	zero point nine five	twenty-four point five	eighty-four	one hundred and sixteen point six	one hundred and sixty-one point two	two hundred and two point two
Boiling point (K)	four point two five	twenty-seven point three	eighty-seven point five	one hundred and twenty point three	one hundred and sixty-six point one	two hundred and eight point two
Solubility (mol/L, 293K)	thirteen point eight	fourteen point seven	thirty-seven point nine	seventy-three	one hundred and ten point nine	-
Critical temperature (K)	five point two five	forty-four point four five	one hundred and fifty-three point one five	two hundred and ten point six five	two hundred and eighty-nine point seven five	three hundred and seventy-seven point six five
Gasification heat (kJ/mol)	zero point zero nine	one point eight	six point three	nine point seven	thirteen point seven	eighteen

nature	He	Ne	Ar	Kr	Xe	Rn
Atomic number	two	ten	eighteen	thirty-six	fifty-four	eighty-six
Atomic weight	four	twenty point one eight	thirty-nine point nine five	eighty-three point eight zero	one hundred and thirty-one point three	two hundred and twenty-two
Valence electron structure	1s	2s2p	3s3p	4s4p	5s5p	6s6p
Atomic (van der Waals) radius (pm)	one hundred and twenty-two	one hundred and sixty	one hundred and ninety-one	one hundred and ninety-eight	-	-
The first ionization potential (kJ/mol)	two thousand three hundred and seventy-two	two thousand and eighty-one	one thousand five hundred and twenty-one	one thousand three hundred and fifty-one	one thousand one hundred and seventy	one thousand and thirty-seven
The second ionization potential (kJ/mol)	five thousand two hundred and fifty	three thousand nine hundred and fifty-two	two thousand six hundred and sixty-six	two thousand three hundred and fifty	two thousand and forty-six	-
Constant pressure heat capacity C p (J/K·mol)	twenty point seven nine	twenty point seven nine	twenty point seven nine	twenty point seven nine	twenty point seven nine	twenty point seven nine
Heat capacity quotient C p / C V	one point six five	one point six four	one point six six	one point six nine	one point six seven	-

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With the development of industrial production and science and technology, rare gases are more and more widely used in industry, medicine, cutting-edge science and technology and even in daily life.

Some production departments often use rare gases as protective gases due to their extremely inactive chemical properties. For example, argon is often used as a shielding gas in the welding of precision parts or active metals such as magnesium and aluminum, and in the manufacturing of semiconductor transistors. atomic reactor Plutonium, a nuclear fuel, will also be rapidly oxidized in the air, and it also needs to be machined under the protection of argon. Filling argon in the bulb can reduce the gasification of tungsten wire and prevent tungsten wire oxidation, so as to extend the service life of the bulb. Helium is Gas chromatography In Carrier The filling gas of thermometer is used in Geiger counter, bubble chamber and other radiation measuring equipment. Both helium and argon are used as welding arc Protective gas and Base metal Inert shielding gas for welding and cutting. They are also widely used in other metallurgical processes and silicon production in the semiconductor industry.

The rare gas will emit light when it is powered on. The first neon light in the world is made of neon gas (the original meaning of neon light in English is“ Neon lamp ”）。 The red light emitted by neon lamp has strong transmission in the air and can pass through thick fog. Therefore, neon lights are often used on the lights of airports, ports and water and land transportation lines. The lamp tube is filled with argon or helium, which will emit light blue or light red light respectively when it is powered on. Some lamps are filled with a mixture of four gases (three or two) such as neon, argon, helium and mercury vapor. As the relative content of various gases varies, various neon lights are made. Commonly used fluorescent lamps are filled with a small amount of mercury and argon, and coated with fluorescent substances (such as Bittern calcium phosphate ）And made of. When it is powered on, the mercury vapor in the tube will discharge and produce ultraviolet light, which will excite the fluorescent material and make it emit visible light similar to sunlight, so it is also called fluorescent lamp. Krypton can reduce the evaporation rate of filament and is commonly used in Color temperature And more efficient performance incandescent lamps, especially in Halogen lamp Krypton can be mixed with a small amount of iodine or bromine compounds. Xenon is commonly used for Xenon arc lamp , because their Continuous spectrum Similar to daylight. This kind of lamp can be used for movie projectors, car headlights, etc^[10] 。

Various mixtures can be made by using rare gases Gas laser 。 He Ne laser is one of them. The He Ne gas mixture is sealed in a special quartz tube. Under the excitation of the external high-frequency oscillator, the atoms of the gas mixture occur Inelastic collision , energy transfer occurs between excited atoms, and then electronic transitions are generated, and stimulated radiation waves corresponding to the transitions are emitted, Near infrared light 。 He Ne laser can be used in measurement and communication. Noble gases can be used Excimer laser This is because they can form a short-lived excited electron state exciton. These excitons for lasers may be noble gas dimers, such as Ar two 、Kr two Or Xe two It is more likely to be an exciton combined with halogen, such as ArF, KrF, XeF or XeCl.^[11] These lasers produce ultraviolet light with shorter wavelength, wherein the wavelength of ultraviolet light produced by ArF is 193nm, while that of KrF is 248nm. This high frequency laser makes high-precision imaging a reality. excimer laser It has many industrial, medical and scientific uses. Integrated circuit Excimer laser must be used in micro lithography and micro manufacturing. Excimer lasers are also needed for laser surgery, such as angioplasty and eye surgery.^[11]

Helium is the lightest gas besides hydrogen, which can be installed in airships instead of hydrogen and will not ignite or explode. The boiling point of liquid helium is - 269 ℃, which is the most difficult to liquefy among all gases. With liquid helium Absolute zero (- 273.15 ℃). Helium is also used to replace nitrogen as artificial air for divers to breathe, because more nitrogen will be dissolved in the blood when breathing with ordinary air in the deep sea with high pressure. When the diver rises from the deep sea and the body gradually recovers to normal pressure, the nitrogen dissolved in the blood will be released to form bubbles, which will block the microvessels and cause "gas blockage". The solubility of helium in blood is much smaller than that of nitrogen, so the above phenomenon will not occur if helium and oxygen mixture (artificial air) is used instead of ordinary air. Liquid helium with temperature above 2.2K is a normal liquid, which has the general property of ordinary liquid. Liquid helium below 2.2K is a superfluid with many abnormal properties. For example, it has superconductivity and low viscosity. Its viscosity becomes one percent of the viscosity of hydrogen, and this liquid helium can flow up along the inner wall of the container, and then slowly flow down along the outer wall of the container. This phenomenon is of great significance for the research and verification of quantum theory.

Argon after high-energy cosmic rays It will occur after irradiation ionization 。 Using this principle, you can Artificial earth satellite A counter filled with argon is set in the. When a man-made satellite flies in space, argon is exposed to cosmic rays. The stronger the irradiation, the stronger the ionization of argon. The radio set on the satellite sends these ionization signals back to the earth automatically, and people can judge the position and intensity of the space cosmic radiation belt according to the size of the signal.

Krypton energy absorption X-ray , which can be used as a shading material for X-ray work.

Xenon lamp It also has high ultraviolet radiation, which can be used in medical technology. Xenon can dissolve in the lipid of cytoplasm, causing anesthesia and expansion of cells, thus temporarily stopping the function of nerve endings. A mixture of 80% xenon and 20% oxygen has been tried as an anesthetic without side effects. In the atomic energy industry, xenon can be used to test the existence of high-speed particles, particles, mesons, etc.

Krypton and xenon isotopes are also used to measure cerebral blood flow.

Radon is the only natural radioactivity When acting on the human body, the gas and radon will quickly decay into radon daughters that can be absorbed by the human body respiratory system Cause radiation damage and induce lung cancer. Thorium impurities in inferior decoration materials will decay Radon gas is released, causing harm to human body. External radiation mainly refers to the biological effect produced by the radiators in natural stone when they directly irradiate the human body, which will damage the hematopoietic organs, nervous system, reproductive system and digestive system in the human body. However, radon also has its uses. The beryllium powder and radon are sealed in the tube. The alpha particles emitted during radon decay react with beryllium nuclei, and the neutrons generated can be used as the neutron source in the laboratory. Radon can also be used as a gas tracer to detect pipeline leakage and study gas movement.

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