Helium is a kind of rare gas. The name of the element comes from the Greek word, the original meaning is “the sun“. In 1868, Janssen of France used a spectroscope to observe the surface of the sun and found a new yellow line, which is considered to belong to an unknown element in the sun. Helium is usually a colorless, odorless gas, not only at normal atmospheric pressure at the curing material. Helium is the most inactive element. The application of ruthenium is mainly used as a working fluid for protective gas, air-cooled nuclear reactors, and ultra-low temperature refrigerants.

In addition, since the density is smaller than air and the properties are stable, helium can also be used as a buoyant gas.

Physical Properties

Basic Information

The element symbol He, atomic number 2, atomic quantity 4.002602 (Helium 4), is a kind of rare gas. The name of the element comes from the Greek word, the original meaning is “the sun.”

There are two kinds of natural isotopes: Helium3, Helium4, and Helium in nature are basically Helium 4. The relative atomic mass is 4.003. In 1868, a spectroscope was used to observe the surface of the sun, and a new yellow line was found, which is considered to belong to an unknown element in the sun. The content of cesium in the air is 0.0005%.

helium balloons

Helium Under normal circumstances, it is a colorless, odorless gas; melting point -272.2°C (25 atmospheres), boiling point -268.9°C, density 0.1785 g/liter, critical temperature -267.8 °C, critical pressure 2.26 atmosphere; water solubility 8.61 cm 3 /kg water.

Helium Gas

It is one of the inert elements and its molecular formula is He. It is a rare gas, colorless, odorless and tasteless. Its solubility in water is the smallest of the known gases, and it is also the gas with the lowest density except for hydrogen. Density 0.17847 g/liter, melting point -272.2 °C (25 atmospheres ).

The boiling point is -268.9 °C. It is the most difficult gas to liquefy and has a critical temperature of -267.9 °C. The critical pressure is 2.25 atm. When the temperature after liquefaction falls below -270.98 °C, the surface tension is small, the thermal conductivity is strong, and almost no viscosity is exhibited.

Liquid helium can be used to obtain low temperatures close to absolute zero (-273.15 °C). The chemical nature is very inactive, neither burning nor supporting combustion. Helium is also the most difficult gas to liquefy.

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Helium Under normal circumstances, it is a colorless, odorless gas. It is the only substance that cannot be cured at standard atmospheric pressure. When the temperature drops to 2.18K, the liquid enthalpy becomes a superfluid and can flow upward along the wall of the vessel. The thermal conductivity is 800 times that of copper and becomes a superconductor, its specific heat capacity, surface tension, and compressibility are both unusual.

Due to the ultra-low temperature of liquid helium, many wonderful physical phenomena occur 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 lower temperatures through liquid helium, and study what happens to various substances at low temperatures, and there are properties that we don’t know yet. This creates a new branch of physics – cryogenic physics.

Super Fluidity

Heike Kamerlingh Onnes was the first scientist to get liquid helium. He further lowered the temperature and tried to get the solid helium, but it did not succeed (the solid-state was first obtained in 1926 by the method of lowering the temperature and increasing the pressure).

For a typical liquid, the density gradually increases as the temperature decreases.  Heike Kamerlingh Onnes lowered the temperature of the liquid helium and increased the density of liquid helium. However, when the temperature dropped to minus 271 °C, the liquid helium suddenly stopped foaming, and the density suddenly decreased.

Superconducting Phenomenon

Place a shot on a lead ring at the temperature of the liquid helium. The shot puts like a weight loss and floats on the ring, keeping a certain distance from the ring. At the same temperature, tie the magnet with a thin chain and slowly place it on a metal dish.

When the magnet is about to hit the plate, you can observe that the chain is loose and the magnet floats on the plate. If you tap the magnet gently, it will rotate on its own. This phenomenon can only be observed at low temperatures and does not occur at high temperatures.

sun fusion

This is a superconducting phenomenon at low temperatures. Some metals in the liquid helium temperature, the movement of the nucleus almost stops, the hindrance to electrons becomes very small, so the resistance will disappear and become a superconductor since the magnetic lines of force cannot pass through the superconductor, it forms between the superconductor and the magnet.

With a large magnetic field, the repulsive force of the magnetic field holds the shot and the magnet, causing them to float in midair. This is the Meissner effect (Meissner Effect), this effect can be used to manufacture the magnetic levitation train.

Chemical Properties

Niobium is the most inactive element of all elements, and it is extremely difficult to form a compound because the distance from the nucleus to the electron layer of the niobium is small and a stable structure is achieved. Its nature determines its use, and its application is mainly as a protective gas, a working fluid for air-cooled nuclear reactors and ultra-low temperature refrigerants.

On February 6, 2017, Wang Huitian and Zhou Xiangfeng from Nankai University in China and their collaborators published a paper on the synthesis of sodium bismuth compound Na2He under high pressure conditions in Nature Chemistry, ending helium The history of elements without compounds indicates that China has reached the forefront in the field of rare gas chemistry.

Ionic Compound

The hydrogen ion, chemical formula of HeH+, is a positively charged ion. It was first discovered in 1925 by the reaction of protons and deuterium atoms in the gas phase. It is the strongest known acid with a proton affinity of 177.8 kJ/mol. This ion is also known as a helium hydrogen molecular ion.

Some people think that this substance can exist in natural interstellar matter. This is the simplest heteronuclear ion that can be compared to the homonuclear hydrogen molecule ion H2. Unlike H2, it has a permanent bond dipole moment that makes it easier to express spectral features.

HeH+ cannot be prepared in a condensed phase because it causes it to interact with any anion, molecule, or atom. However, it is possible to predict its acidity in aqueous solution using Gas’s law.

The ionization process – a free energy change of 360 kJ/mol is equivalent to a p K a of -63.

HeH in covalent bond lengths is 0.772 Å.

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Other helium hydrogen ions are known or theoretically studied. HeH2, which has been observed by microwave spectroscopy, has calculated that its affinity is 6 kcal/mol and HeH3 is 0.1 kcal/mol.

Neutral Molecule

Unlike hydrazine ions, neutral molecules composed of hydrogen and helium are generally unstable. However, it is stable as an excimer in the excited state and was first observed in the spectrum in the mid-1980s.

Pka: -63 (presumed), much stronger than fluoroantimonic 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 appear only in “Instantaneous” or only by calculation, so they are still difficult to think of as “Compounds“.

Strontium Compound

The solid stability of the yttrium element stems from its closed-shell electronic configuration. Its outer shell is in a perfect state, with no space and other atoms bonded by shared electrons. But this is the situation in the Earth’s surface environment.

As the second richest element in the universe, cockroaches play an important role in the formation of stars and giant gas planets. Under extreme conditions in outer space or deep in the earth, it may follow unusual rules. Now researchers have just verified this strange phenomenon.

Utah State University co-author Alex Boldyrev said: “Extremely high pressures, such as in the core of the Earth or other giant stars, can completely change the chemical properties of the cockroach.

The researchers used the “crystal structure prediction” model to calculate that a stable sodium-sodium compound could form under extreme pressure. Then they actually created a compound that was never seen before in the diamond pressure chamber experiment: Na2He. The experiment can provide conditions equivalent to 1.1 million times the Earth’s atmospheric pressure for the strontium and sodium atoms.

Helium atom

The result was too unexpected, so it was a huge difficulty when it was published. The researchers spent more than two years trying to convince the reviewers and editors.

Based on these results, the research team predicts that if the pressure reaches 10 million times their experimental level, sodium will easily react with helium to form a stable Na2He. Even more amazingly, the composition of this compound does not require any chemical bonds.

Professor Wang Huitian of Nankai University is the co-communication author of this study. According to him, “The compounds found are very strange: the ruthenium atoms usually do not form any chemical bonds, and the existence of new substances fundamentally changes the chemical mutuality between the sodium atoms. The role of forcing electrons to concentrate in the cubic space of the structure, while having the ability to insulate.”

Helium Recovery System

The crystal structure of Na2He alternates between a sodium atom (purple) and a germanium atom (green), and a region in which electrons (red) are shared.

“This is not really a chemical bond,” Popov said. “But you can make this structure stable. If you remove the atom, the structure will not be stable.”

In this process, the electrons are isolated, and the inner electrons of Na form a strong overlap with the inner 1s electrons of He and the 2s, 2p orbitals of the outer layer. Influenced by the principle of bubble incompatibility, the 1s electron density of He and the distribution of the outer electron orbitals were forced to change, resulting in He obtaining 0.15 electrons during the formation of Na2He.

This work confirmed that He would have a weak chemical activity at high pressure to form a compound with Na which is remarkably enhanced under high pressure.

Although recent breakthroughs in metal hydrogen have met with great doubts, the data in this article is much more solid. Henry Rzepa, a physicist from Imperial College London, said in contrast to the discovery of metal hydrogen: “This is a more reliable science, and bismuth compounds are a major breakthrough.

This research involves scholars from China, the United States, Russia, Italy, and Germany. The Chinese research units involved include Beijing High Voltage Research Center, Northwestern Polytechnical University, Institute of Solid State Physics of the Chinese Academy of Sciences, and Nanjing University.

It is particularly worth mentioning that this research began during the exchange interview between Xiaodong graduate student Xiao Dong in the United States. According to the author’s contribution, Xiao-Dong designed the research work and carried out related calculations. Xiao Dong is currently working at the Shanghai High Voltage Research Center.

It is understood that this work was submitted to Nature in 2013, but the author and the reviewer could not agree on the nature of Na2He, and finally changed to Nature Chemistry. Of course, not everyone is convinced. Edinburgh University Eugene Gregoryanz believes that XRD data needs to be improved, and ultimately depends on whether this work can be repeated by other teams. However, there are few laboratories in the world with qualified conditions.

Helium Isotope

There are eight known strontium isotopes, including helium3, helium4, helium5, helium6, helium8, etc., but only helium3 and helium4 are stable, and the rest are radioactive. In nature, strontium is the most abundant strontium isotope, mostly due to the decay of alpha from other radioactive materials, and the release of helium4 nucleus. On the earth, the content of strontium 3 is extremely small, and they are all produced by the beta decay of Superheavy Hydrogen.

Helium Isotope

Helium-2: Its nucleus has only 2 protons, so far it is only hypothetical particles, but if the strong nuclear force is increased by 2%, it may exist.

Helium-5 is one of the isotopes of yttrium and the element symbol is He. Its nucleus consists of two protons and three neutrons. It is radioactive and emits neutrons with a half-life of 0.6 MeV.

Helium-6: The nucleus contains 2 protons and 4 neutrons, which is very unstable.

Helium-7: The nucleus contains 2 protons and 5 neutrons, which will decay into helium-6, which is very unstable.

Helium-8: The nucleus contains 2 protons and 6 neutrons, which is very unstable.

Helium-9: The nucleus contains 2 protons and 7 neutrons, which is very unstable.

Helium-10: The nucleus contains 2 protons and 8 neutrons, which is very unstable.

Preparation Method

Natural gas separation method: In the industry, the natural gas containing hydrazine is used as raw material, and liquefaction fractionation is repeated, and then activated carbon is used for adsorption purification to obtain pure hydrazine. Ammonia Method: In the synthesis of ammonia, the tail gas from the separation and purification of helium available.

Air fractionation: from the liquid air by fractionation from the helium mixture.

Uranium ore method: The uranium ore containing strontium is calcined to separate the gas, and then chemically removed to remove impurities such as water vapor, hydrogen, and carbon dioxide.

Helium Uses

Because it is light and non-flammable, it can be used to fill airships, balloons, thermometers, tubes, diving suits, and more. It can also be used as a protective gas for atomic reactors and accelerators, lasers, rockets, smelting, and welding. It can also be used to fill bulbs and neon tubes, as well as to make foam.

Because of its low solubility in the blood, it can be added to oxygen to prevent decompression sickness, like a diver’s breathing gas, or to treat asthma and suffocation.

The liquid helium temperature (-268.93 °C) is close to absolute zero (-273 °C), so it is used as a superfluid in superconducting research to make superconducting materials. Liquid helium is also commonly used as a coolant and refrigerant. In medicine, it is used in the treatment of cancer with an argon-helium knife. It can also be used as part of an artificial atmosphere and laser media.


Causing Suffocation

If a large amount of inhalation of helium is caused, the oxygen in the body will be replaced by sputum, and hypoxia will occur (respiratory reflex is driven by excessive carbon dioxide in the receptor and not sensitive to hypoxia), and even severe death. In addition, if helium is directly inhaled from a high-pressure gas cylinder, its high flow rate will seriously damage the lung tissue.

A large amount of high-pressure helium and oxygen can cause high-pressure nervous syndrome (HPNS), but a small amount of nitrogen can handle this problem. Seventy-eight percent of the air is nitrogen, so don’t worry.

According to reports, large and long-term inhalation of hernia can cause brain damage and even death. There is also a small amount of radon in most French fries bags, but don’t worry, no harm.

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Safety Matters – Helium Cylinder

  • The pressure is usually 15MPa. When using it, use a pressure reducer such as YQY-12 or 152IN-125 to decompress and use it. Before use, use soapy water to check the gas pipeline to ensure that the gas pipeline does not leak.
  • Make sure that the helium does not leak and keep the workplace ventilated.
  • The date of production, including the service life, should be recorded on the packaged gas cylinders. All expired cylinders must be sent to a department for safety inspection before they can continue to be used.
  • When using the exhaust gas in each bottle of helium, the residual pressure in the bottle should be kept at 0.5MPa, and the minimum pressure should not be lower than 0.25MPa. The valve should be closed to ensure the gas quality and safety.
  • Bottled helium should be sorted and stacked during transportation, storage, and use.
  • Do not be close to open flames and heat sources, should be close to fire, do not touch oil wax, do not explode, do not throw, do not hit, do not conduct arc or arc on the cylinder.
  • Barbaric loading and unloading is strictly forbidden. For short-distance moving helium cylinders, special trolleys for cylinders should be used, and long-distance moving cylinders should be transported by dangerous goods transport vehicles.
  • The temperature of liquid helium is -268.9 ° C, and contact with the skin can cause severe frostbite.

Adverse reactions of hernia to the human body

When the amount of radon in the body increases and the oxygen content is lower than 19.5%, the patient first has accelerated breathing, inattention, and ataxia; followed by fatigue, irritability, nausea, vomiting, coma, convulsions, and so on. death.