Helium, inactive element, element symbol HeNoble gasOne of.Normally, helium is a colorless and tasteless gas, which is the only gas that cannotStandard atmospheric pressurelowersolidificationSubstances.Helium is mainly used asShielding gasWorking fluid and ultra-low temperature refrigerant of gas cooled nuclear reactor.In addition, due to its lower density than air and stable properties, helium can also be used as a floating gas.
The element name of helium comes from Greek, which originally means "sun"[1]。French in 1868Pierre Janssen Using a spectroscope to observe the sun's surface, a new yellow spectral line was found, which was believed to belong to an unknown element on the sun, hence the name helium.
On February 6, 2017, China Nankai UniversityWang Huitian、Zhou XiangfengThe team and its collaborators《Nature Chemistry》A paper on the synthesis of helium sodium compound Na ₂ He under high pressure was published on[2-3], ending the history of helium without compounds, which marks that China has moved to the forefront in the field of rare gas chemistry.
French astronomer on August 18, 1868Pierre Janssen Go to India to observe the total solar eclipse and observe with a spectroscopeProminenceFrom the red flame protruding from the back of the black moon disk, we can see that there are colorful stripes, which are the hot spectrum emitted by the sun.He found a yellow spectral line, close to the total D1 and D2 lines of sodium spectrum.After the solar eclipse, he also observed this yellow line in the solar spectrum, called D3 line.On October 20, 1868, British astronomerLockyerSuch a yellow line has also been found.
After further research, it is recognized that a new line does not belong to any known element, but is generated by a new element. The new element is named helium, which comes from the Greek helios (sun), and the element symbol is He.This is the first element found outside the earth in the universe.To commemorate this event, a gold commemorative plate was cast at that time, with the legendary sun god driving a four horse chariot carved on one sideApolloThe other side is carved with the heads of Pierre Janssen and Lockyer, and the following is written: Analysis of the solar protrusion on August 18, 1868.When Jason found helium in the solar spectrum, the British JN. Lockyer and EF. Frankland believed that this material had not been found on the earth, so it was named "helium" (h é lium in French and helium in English), which originated from \\\\\\\\\\\\\\\\\\.
After more than 20 years, Ramsay discovered a mysterious gas when he studied uranium yttrium.As he studied the spectrum of this gas, he found that it might be the yellow D3 line discovered by Pierre Jansen and Lockyer.But because he had no instrument to determine the position of spectral lines in the spectrum, he had to turn to one of the best spectroscopists at that time, London physicist Croix.Krux proved that this gas is helium.So helium was also found on Earth.[4]
In the early decades of the twentieth century, all countries in the world were looking for helium resources, mainly to fill airships at that time.But in the 21st century, helium is not only used in flight, cutting-edge scientific research and modern industrial technology, but also liquid helium rather than gaseous helium.Liquid helium leads people to a new field - the cryogenic world.
The British physicist Dewar first obtained liquid hydrogen in 1898.In the same year, the Dutch physicist Kamelin Ones also got liquid hydrogen.The boiling point of liquid hydrogen is - 253 ℃. At such a low temperature, other gases not only become liquids, but also become solids.Only helium is the last gas that refuses to become a liquid.Scientists including Dewar and Kamelin Ones decided to turn helium into liquid.
On the evening of July 13, 1908, Heike Kamerlingh Onnes, a Dutch physicist, and his assistants succeeded in the famous Leiden Laboratory, where helium turned into liquid.He got 320 cubic centimeters of liquid helium for the first time.
To get liquid helium, helium must be compressed and cooled to the temperature of liquid air, and then expanded to further reduce the temperature, so that helium becomes liquid.Liquid helium is a unique liquid with a boiling point of minus 269 ℃.At such a low temperature, hydrogen also becomes a solid. When contacting with air, the air will immediately freeze on the surface of liquid helium to form a hard cover.
In 1934, Kabiza, a former Soviet scientist who studied in Rutherford, England, invented a new type of liquid helium machine, which can produce 4 liters of liquid helium per hour.Later, liquid helium was widely studied and applied in laboratories in various countries.
Content distribution
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Helium exists in the whole universe, accounting for 23% by mass, second only tohydrogen。However, it mainly exists in natural gas or radioactive ore in nature.EarthlyatmosphereThe concentration of helium is very low, only one in 52000.The helium contained in the radioactive minerals on the earth isAlpha decayThe product of.Helium in some natural gas contains an economically valuable amount, up to 7%. In the United States, there is about 1% helium in natural gas. Every cubic meter of air on the surface contains 4.6 cubic centimeters of helium, accounting for about 0.0005% of the whole volume. The density is only one 7.2 times that of air, which is the smallest gas except hydrogen.
Content in the crust
0.008（ppm）
The content of elements in the sun
230000（ppm）
Content of elements in seawater
0.000006（ppm）
Helium on the earth is mainlyradioactive elementThe product of decay, alpha particle is heliumNucleus。It can be extracted from natural gas containing up to 7% helium in industry.It can also be used in liquid airfractionationIt is made from He Ne gas mixture.[4]
physical property
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essential information
Atomic spectrum of helium
Element symbol He, atomic number 2, atomic weight 4.002602 (helium-4), is a kind of rare gas.The element name comes from Greek, which originally means "sun".
Helium after electrification
Helium has two natural isotopes:helium-3 、Helium-4Helium in nature is basically helium-4.The relative atomic mass is 4.003.In 1868, someone observed the sun's surface with a spectroscope and found a new yellow spectral line, which was believed to belong to an unknown element on the sun, so it was named helium.The content of helium in air is 0.0005%.
Helium is usually a colorless and odorless gas;Melting point - 272.2 ℃ (25 atmospheres), boiling point - 268.9 ℃;Density 0.1785g/L, critical temperature - 267.8 ℃, critical pressure 2.26 atmosphere;Water solubility 8.61 cm ³/kg water.
Helium isInert elementOne, the molecular formula is He, which is aNoble gas, colorless, odorless and tasteless.Its solubility in water is the smallest among known gases, and it is also the gas with the smallest density except hydrogen.Density 0.17847g/L, melting point - 272.2 ℃ (25 atmospheres).Boiling point - 268.9 ℃.It is the most difficult gas to liquefy, and its critical temperature is - 267.9 ℃.The critical pressure is 2.25 atmospheres.When the temperature drops below - 270.98 ℃ after liquefaction, it has very small surface tension, strong thermal conductivity and almost no viscosity.Liquid helium can be used to obtain low temperatures close to absolute zero (- 273.15 ℃).The chemical property is very inactive, which can neither burn nor support combustion.Helium is also the most difficult gas to liquefy.
Helium is usually a colorless and tasteless gas.It is the only material that cannot be solidified under standard atmospheric pressure.Liquid heliumWhen the temperature drops to 2.18K, the property changes abruptly, becoming aSuperfluidIt can flow upward along the vessel wall, its thermal conductivity is 800 times that of copper, and it becomes a superconductor;Its specific heat capacity, surface tension and compressibility are abnormal.[4]
Because of the super low temperature of liquid helium, many wonderful physical phenomena appear at this temperature.Many important physical experiments are carried out at low temperatures.Physicists all over the world are studying liquid helium, hoping to reach a lower temperature through liquid helium to study what will happen to various substances at low temperatures and what properties we still do not know.This led to a new branch of physics - low-temperature physics.[5]
melting point
-272.2 ℃ (25 atmospheres);
boiling point
-268.9℃；
density
0.1785g/L
critical temperature
-267.8℃
critical pressure
2.26 Atmospheric pressure
Thermal conductivity
151.3W/（m·K）
crystal structure
The unit cell is hexagonal unit cell
Helium-4
The following table shows some basic physical properties of liquid helium (Helium 4) (the state of some parameters is unknown):
Evaporation heat/kJ/kg
twenty point seven three
Specific heat/kJ/(kg · K)
four point five six
Viscosity/MPa · s
three point five seven
Dielectric constant
one point zero four nine two
Critical temperature/K
five point two zero one
Critical pressure/MPa
zero point two two seven
helium-3
Helium-3 is a stable isotope of helium in nature. Its atomic weight is 3.016, and its nucleus consists of two protons and one neutron.Normally, helium-3 is a colorless, odorless, non-toxic, non combustible inert gas.
The following table shows some basic physical properties of liquid helium (Helium 3):
Normal boiling point/K
three point one nine one
Density/kg/m ³
eighty-two point three
Evaporation heat/J/mol
twenty point five six
Specific heat at 1.0K/J/(mol · K)
four point two two two
Viscosity at 3.2K/mPa · s
three point five seven
Thermal conductivity at 3.2K/mW/(m · K)
twenty
Critical temperature/K
three point three two four
Critical pressure/MPa
zero point one one five
Superfluidity
Kamelin Ones was the first scientist to obtain liquid helium.He further lowered the temperature and tried to obtain solid helium, but failed (solid helium was first obtained by Kisom in 1926 by lowering the temperature and increasing the pressure).
For general liquids, the density will gradually increase as the temperature decreases.Kamelin Ones reduced the temperature of liquid helium and increased the density of liquid helium.However, when the temperature drops to minus 271 ℃, liquid helium suddenly stops bubbling and its density suddenly decreases.
This is another kind of liquid helium.Kamelin Ones called the former bubbling liquid helium Helium I, and the latter static liquid helium Helium II.
Press a small glass into helium II.The glass gradually filled from empty.Take out the small glass containing liquid helium and hang it in the air. Liquid helium appears under the glass. Soon, the liquid helium in the glass "leaks" out.
Helium II can flow backwards, it will flow backwards along the wall of the glass.This phenomenon can only occur at low temperature. It is called“Superfluidity”Helium II with "superfluidity" is calledSuperfluid。
Later, many scientists studied this strange phenomenon and made many new discoveries.For example, the helium knife fountain discovered by Alan et al. in 1938.In a glass tube, there is very fine emery, and a thin nozzle is connected to the top.Immerse the glass tube into Helium II, illuminate the thick lower part of the glass tube with light, and the thin nozzle will eject the fountain of Helium II. The stronger the light is, the higher the spray will be, which can be as high as several centimeters.
Helium II fountain is also a special property of superfluid.In this experiment, light energy is directly transformed into mechanical energy.[4]
Superconductivity phenomenon
Place a shot on a lead ring at the temperature of liquid helium.The shot put will float on the ring like weightlessness, keeping a certain distance from environmental protection.At the same temperature, tie the magnet with a thin chain and slowly put it into a metal plate.When the magnet is about to touch the plate, it can be observed that the chain is loose and the magnet floats on the plate. If the magnet is gently tapped at this time, it will rotate by itself.This phenomenon can only be observed at low temperatures and will not occur at high temperatures.
This is a superconducting phenomenon at low temperatures.When some metals are at the temperature of liquid helium, the movement of the atomic nucleus almost stops, and the obstruction to electrons becomes very small, so the resistance will disappear and become superconductors;Because it is impossible for magnetic lines of force to pass through superconductors[6]So a large magnetic field is formed between the superconductor and the magnet. The repulsive force of the magnetic field holds the shot and magnet, making them float in the air.This is it.Meisner effect(Meissner Effect), this effect can be used to createMagnetically Levitated Train。
chemical property
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Helium is the most inactive element among all elements, and it is extremely difficult to form compounds because of itsNucleusThe distance to the electron layer is very small, and a stable structure is achieved.Its nature determines its use. Helium is mainly used as a protective gas, working fluid of gas cooled nuclear reactors and cryogenic refrigerants.
On February 6, 2017, China Nankai UniversityWang Huitian、Zhou XiangfengThe team and its collaborators《Nature Chemistry》The report on the synthesis of helium sodium compound Na under high pressuretwoHe's paper[2-3], ending the history of helium free compounds, marking that China has reached the forefront in the field of rare gas chemistry.
Conjecture of fluoride production
Pimental et al proposed the preparation of HeF by nuclear transformation based on the fact that the electronic arrangement of HeF ₂ is similar to that of stable HF ₂ ⁻twoThree methods of.
1. Beta decay method of tritium
Tritium should become helium after beta decay.In this way, tritium compounds may become helium compounds after beta decay.In order to facilitate the reaction, tritium is first fixed in the solid lattice of KHF ₂ through the return of tritium and hydrogen isotopes.After the TF ₂ ⁻ trapped in the lattice undergoes nuclear reaction, HeF ₂ will be generated.
TFtwo⁻ → HeFtwo+β⁻
The recoil energy of tritium in the process of decay will not cause the newly formed helium difluoride chain to break.The half-life of tritium decay is 12.25 years. It is estimated that the tritium of ¹ ϕ Ci can only generate 10 μ mol HeF after 4-5 monthstwo。
2. Thermal neutron irradiation method
Irradiate LiF with thermal neutrons to generate nuclear reaction:
After Li (n, α) reaction, the generated helium nucleus is the same as F in the parent lattice-Combine to generate HeFtwo。
3. Prepare HeF ₂ by bombarding solid fluorine with alpha particles directly
From this point of view, among the three methods, the first method is the most likely to produce HeF ₂, but no report has been seen so far.Malm et al. believed that although the electron arrangement of HeF ₂ and HF ₂ ⁻ is similar, HF ₂ ⁻ is a compound formed by the interaction of H ⁻ with two F atoms. The ionization potential of H ⁻ is only 0.7 eV, while the ionization potential of helium is as high as 25 eV, so it is doubtful whether HeF ₂ exists.[4]
Ionic compound
Helium hydrogen ion, chemical formula HeH++, is a positively charged ion.It was first discovered in 1925 byprotonAnd helium atoms in the gas phase.It is the strongest acid known, with a proton affinity of 177.8 kJ/mol.This ion is also called helium hydrogen molecular ion.Some people think that this kind of matter can exist in natural interstellar matter.This is the simplest heteronuclear ion, which can be compared with homonuclear hydrogen molecular ion HtwoCompare.And HtwoThe difference is that it has a permanent bond dipole moment, which makes it easier to show spectral characteristics.
HeH+It cannot be prepared in condensed phase because it will interact with any anion, molecule or atom.However, its acidity in aqueous solution can be predicted by Gass law.
The free energy change of - 360 kJ/mol in the ionization process is equivalent to pKA is - 63.
The covalent bond length of HeH is 0.772 ∨.
Other helium hydrogen ions have been known or studied theoretically.HeH ₂, which has been observed by microwave spectrum, scientists calculated that its affinity energy is 6 kcal/mol, while HeHthreeIs 0.1 kcal/mol.[5]
Neutral molecule
Unlike helium hydrogen complex ion, neutral molecule composed of hydrogen and helium is very unstable in general.However, as an excimerexcited stateIt is stable and was first observed in the spectrum in the mid-1980s.
pKa: - 63 (presumably), much stronger than fluostimonic acid.
HHe（g）
→
H（g）
+ He（g）
+178 kJ/mol
HHe（aq）
HHe（g）
+973 kJ/mol
H（g）
H（aq）
– 1530 kJ/mol
He（g）
He（aq）
+19 kJ/mol
HHe（aq）
H（aq）
+ He（aq）
– 360 kJ/mol
Even so, these ions or molecules only appear in the "instant" or are only calculated, so they are still difficult to be considered as "compounds".[5]
Helium sodium compound
On February 6, 2017, China Nankai UniversityWang Huitian、Zhou XiangfengThe team and its collaborators《Nature Chemistry》The report on the synthesis of helium sodium compound Na under high pressuretwoHe's paper[2-3], ending the history of helium free compounds, marking that China has reached the forefront in the field of rare gas chemistry.
Previously, researchers had found a way to pair other elements with helium.But for a long time, no stable substance has been formed.The most common example is the van der Waals force between helium and other elements, which can exist without covalent bond or ionic bond.At extremely low temperatures, helium can indeed form van der Waals force, but it is extremely weak and cannot be maintained for a long time.[2-3]
The strong and stable force of helium comes from its closed shell electronic configuration: its shell is in a complete state, and there is no space to combine with other atoms by sharing electrons.But this is the case in the environment of the earth's surface.
As the second abundant element in the universe, helium plays an important role in the formation of stars and giant gas planets.Under extreme conditions in outer space or deep earth, it may follow unusual rules.Now, researchers have just verified this strange phenomenon.
Alex Boldyrev, co-author of the Utah State University article, said: "Extreme pressure, such as in the core of the Earth or other giant stars, can completely change the chemical properties of helium."
The researchers calculated through the "crystal structure prediction" model and found that a stable helium sodium compound can be formed under extreme pressure.Then they really created a compound that had never been seen before: NatwoHe。Experiments can provide helium and sodium atoms with conditions equivalent to 1.1 million times the earth's atmospheric pressure.[2-3]
This result was so unexpected that it was difficult to publish it. Researchers spent more than two years persuading reviewers and editors.
Based on these results, the research team predicted that if the pressure reached 10 million times their experimental level, sodium would easily react with helium to generate stable NatwoHe。What's more, the composition of this compound does not require any chemical bond.
Professor Wang Huitian of Nankai University is the co corresponding author of this study. According to him, "the compounds found are very strange: helium atoms usually do not form any chemical bonds, and the existence of new substances fundamentally changes the chemical interaction between sodium atoms, forcing electrons to concentrate in the cubic space of the structure, while having insulation ability."[2-3]
NatwoThe crystal structure of He is composed of sodium atoms (purple) and helium atoms (green) alternately, and the shared electrons (red) exist in the region between them.[2-3]
helium
"It's not really a chemical bond," Popov said, "but helium can stabilize this structure. If you remove the helium atom, the structure will not remain stable."
The following are other manifestations of the compound. In the left figure, pink is sodium and white is helium;In the figure on the right, sodium and helium form a cube, and the red dots are electrons.[2-3]
helium
Sublattice analysis shows that the occupation of He leads to the localization of electrons into the atomic gap and the formation of multi center bonds under the gravity of Na atomic nucleus, thus the whole system becomes an electronic salt system.In this process, the isolated electrons, the inner electrons of Na, the inner 1s electrons of He and the outer 2s, 2p orbitals of He produce strong overlap.Under the influence of Pauli incompatibility principle, the 1s electron density of He and the distribution of outer electron orbit are forced to change, resulting intwoHe obtained 0.15 electrons in the process of He formation.This work confirmed that He has weak chemical activity under high pressure and can form compounds with Na, which has significantly enhanced reducibility under high pressure.[2-3]
Although the breakthrough research on metal hydrogen has met with great doubts recently, the data in this article is much more solid.Henry Rzepa, a physicist from Imperial College London, said when comparing this research with the discovery of metal hydrogen: "This is a more reliable science, and helium compound is a major breakthrough."[3]
This research involves scholars from China, the United States, Russia, Italy and Germany.The participating Chinese research institutions areBeijing High Voltage Scientific Research Center、Northwestern Polytechnical UniversityInstitute of Solid State Physics, Chinese Academy of SciencesNanjing University。It is worth mentioning that this research began during the exchange visit of Nankai University graduate Xiao Dong in the United States. According to the author's contribution, Xiao Dong designed the research work and carried out relevant calculations.Xiao Dong has already worked in Shanghai High Voltage Scientific Research Center.[3]
It is understood that this work was submitted to Nature in 2013, but the author and reviewertwoHe Chengjian could not reach an agreement on the nature of his health, so he finally changed to Nature Chemistry for publication.Of course, not everyone is convinced.Eugene Gregoryanz of Edinburgh University thinks that the XRD data needs to be improved, and finally it depends on whether this work can be repeated by other teams.However, there are few qualified laboratories in the world.[3]
isotope
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There are eight known helium isotopes, including helium-3, helium-4, helium-5, helium-6, helium-8, etc., but only helium-3 and helium-4 are stable, and the rest are radioactive.In nature, helium-4 is the most common helium isotope, mostly derived from other radioactive materialsAlpha decay, emitting helium-4 nuclei.On the earth, there is very little helium-3, which is mainly composed ofSuperheavy hydrogen(tritium).
It's heliumisotopeOne, the element symbol is He.Its nucleus consists of two protons and three neutrons.Withradioactivity, will emit neutrons, whichhalf lifeIs 0.6 MeV.
Helium-6
The nucleus contains two protons and four neutrons, which is very unstable.
Helium-7
The nucleus contains two protons and five neutrons, which will decay into helium-6, which is very unstable.
Helium-8
The nucleus contains two protons and six neutrons, which is very unstable.
Helium-9
The nucleus contains two protons and seven protonsneutron, very unstable.
Helium-10
The nucleus contains two protons and eight neutrons, which is very unstable.
remarks:The data marked with # represents theoretical speculation without experimental proof, while the data enclosed in parentheses represents data uncertainty.
purpose
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Because helium is light and nonflammable, it can be used to fill airships, balloons, thermometers, electronic tubes, diving suits, etc.It can also be used as a protective gas for atomic reactors and accelerators, lasers, rockets, smelting and welding, as well as for filling light bulbs and neon tubes, and also for making foamed plastics.
Helium can be added to oxygen to preventDecompression sickness, used as breathing gas for divers, or to treat asthma and suffocation.
The temperature of liquid helium (- 268.93 ℃) is close toAbsolute zero(- 273 ℃), so it is used as a superfluid in superconducting research to make superconducting materials.Liquid helium is also commonly used as coolant and refrigerant.In medicine, forArgon helium knifeTo treat cancer.It can also be used as a component of artificial atmosphere and laser media.[4]
danger
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Cause suffocation
If a large amount of helium is inhaled, oxygen in the body will be replaced by helium, resulting in hypoxia (the respiratory reflex is driven by excessive carbon dioxide in the body, and is not sensitive to hypoxia), and even death will occur in serious cases.In addition, if helium is directly inhaled from the high-pressure gas cylinder, its high flow rate will seriously damage the lung tissue.A large amount of high-pressure helium and oxygen will cause the high pressure nervous syndrome (HPNS), but a small amount of nitrogen can deal with this problem.And 78% of the air is nitrogen, so don't worry.It is reported that inhalation of helium in large quantities and for a long time can lead to brain damage and even death.There is also a small amount of helium in most French fries packaging bags, but don't worry, there is no harm.
Safety precautions - helium cylinder
1. The pressure is usually 15MPa, which shall be reduced by YQY-12 or 152IN-125 pressure reducer before use. Soap water shall be used to check the gas pipeline before use to ensure that the gas pipeline is free of gas leakage.
2. Ensure no helium leakage and keep the workplace ventilated.
3. The production date, including service life, shall be marked on the packed gas cylinders. The expired gas cylinders must be sent to the department for safety inspection before they can continue to be used.
4. When each bottle of helium is used for tail gas, the residual pressure in the bottle shall be kept at 0.5MPa, and the minimum residual pressure shall not be less than 0.25MPa. The bottle valve shall be closed to ensure gas quality and use safety.
5. Bottled helium shall be classified and stacked during transportation, storage and use.
6. Do not get close to open fire and heat source. Do not get close to the fire, touch oil wax, expose to the sun, throw again, or hit. Do not strike an arc or arc on the cylinder body.
7. Rough loading and unloading is strictly prohibited. For short distance moving helium steel cylinders, special trolley for steel cylinders shall be used. For long distance moving steel cylinders, dangerous goods transport vehicles shall be used.
8. The temperature of liquid helium is - 268.9 ℃. Contact with skin can cause severe frostbite.
