Helium Element Properties and Information
Helium Element Properties and Information
Helium is the second element on the periodic table. Elements are arranged in the periodic table on the basis of atomic number. Atomic number is the number of protons in the nucleus of the atom. Helium has an atomic number of 2. It is located in the Group 18 and Period 1 of the periodic table of elements. It is denoted by He. The name is derived from Greek ‘Helios’ which means titan of the sun. It is the first gas in the noble gas group in the periodic table.
George Rayet, Captain C.T. Haig, Norman R. Pongson, Lieutenant John Herschel were the first to detect helium as an unknown, yellow spectral line in the sunlight during a solar eclipse in 1868. This spectral line was further subsequently confirmed by Jules Janssen, he travelled to India to record the spectral line during the same solar eclipse. In Britain, Norman Lockyer also observed it during the same solar eclipse and he was the first person to propose that the unknown spectral line was due to a new element. It was him who named it helium. Helium was discovered formally when two chemists Per Teodor Cleve and Nils Abraham Langlet found it emanating from cleveite in 1895. Cleveite is an uranium ore, also independently, Sir William Ramsay detected the presence of helium in the same year from the gas given out when an uranium ore was treated with acid.
Helium is the second most abundant element in the universe. Among all the detectable matter, helium makes up to 23% of total matter by mass. Helium is formed on earth by the process of natural radioactive decay, since it is very light it migrates to the surface of earth, enters the atmosphere and then leaves earth and leaves into the outer space at roughly the same rate it was formed. Hence helium is said to be rare on earth, its amount is only about 5.2 ppm by volume of the atmosphere.
Physical Properties
- It is a colourless, odourless, tasteless, non-toxic, inert and a monoatomic gas.
- The atomic mass of helium is 4.003
- The melting point of helium is -272.2°C
- The boiling point of helium is -268.9°C
- The density of helium is 0.1786 in S.I. units at STP
- In total there are nine known isotopes of helium but only helium-3 and helium-4 are stable.
- Helium is the least water soluble among all the monoatomic gases.
- If helium is made to expand at normal ambient temperature then it is seen that it heats up while freely expanding.
- A unique property of helium is that when it is cooled to absolute zero at ambient pressure, it doesn’t solidify, it stays as a liquid. It acquires very different properties and is called a superfluid. The viscosity of superfluid helium is zero.
Chemical Properties
- Helium is the second least reactive element among all the elements.
- It conducts electricity only when it is ionized.
- When helium is reduced to plasma it can react with fluorine, iodine, tungsten, sulfur and phosphorus to form unstable compounds known called excimers.
- Helium hydride ion, which is essentially helium bonded to hydrogen atom with one electron removed is the strongest Brønsted acid. It has the capacity to protonate any molecule or counterion it comes in contact with.
Methods of Production
- Source: Since only a fraction of air is helium, it is infeasible and highly uneconomical to separate it from air. All the helium is dug from beneath the earth. Natural gas may contain up to 7% helium depending on from which location it is obtained. All the major requirements for helium are fulfilled by separating it from natural gas.
- Fractional Distillation: Helium is produced in bulk all around the world by the process of fractional distillation of natural gas. Helium has very low boiling point hence all the gases which have boiling points greater than helium are removed by liquefying them under the conditions of low temperatures and high pressures. Treating the gas with activated charcoal is used as purification after that, it results in high grade helium having purity of about 99.995%. Lastly for the purpose of ease of transportation the helium is cryogenically liquefied resulting in liquid helium.
- Membranes: Special types of semipermeable membranes are used to separate helium from natural gas. The separation process is largely governed by the process of diffusion.
- Bombardment: Theoretically it is possible to synthesise helium by bombardment of boron or lithium. Helium has been prepared by bombarding deuterons on lithium in labs but it is completely uneconomical to make it into a large scale process.
Relevance in Chemical and Related Industries
- In Leak Detection: Leak detection using helium is pretty much a standard wherever vacuum equipments are used. Helium is excellent for leak detection due to its large diffusion coefficient and low viscosity. It is also quite prevalent in semiconductor and electronics industries and also in large rocket engines because helium leak detectors can detect leaks which are thousands of times smaller than what other devices can detect. Helium leak detectors can be calibrated to detect leaks which are even smaller than the volume equivalent to one drop of water per year.
Relevance in Other Industries
- For Cryogenics: This is the largest known use of helium all around the world. Due to its very low boiling point it is used in cryogenics, complex cooling systems and refrigeration. All the devices which utilize superconductors are required to keep the temperature of superconductors very low for it to work, helium refrigerants are most economical for such devices. Magnetic Resonance Imaging (MRI) and Semiconductor Processing are two examples where helium is used as a refrigerant.
- In Rockets: Helium is used to pressurise the propellant tanks for the engines. The propellants used is a mixture of hydrogen and oxygen hence helium is a good choice for the pressurising gas. The pressure is provided in order to avoid pump cavitation and also to pressurise enough so that it can withstand vehicle imposed structural loads. Also, helium gas is used for the purging of the propellant feed system for liquid hydrogen engines. If any other gas is used apart from helium then it will freeze and clog the system.
- In Welding: In many types of welding and also in laser devices the helium acts as a shielding gas. It prevents atmospheric contamination of the metals and it also stabilises the arc.
- Optical Fiber Industries: The manufacturing of optical fibers critically depend on the use of helium gas. A large rod is pulled to form fibers, during the drawing process several layers of cladding is also coated on the fiber. The coating is done using Modified Chemical Vapour Deposition (MCVD). Helium is mixed with the MCVD gas because helium is inert and also has very good thermal conductivity hence it helps in uniforming the cladding. Helium is also used during chilling of the optical fibers because of their good thermal conductivity they act as very conductive thermal contact also they don’t form bubbles in the glass hence they don’t decrease the fiber’s transmission properties.
- For Transportation: Helium is a very light gas. One of the very first applications of helium was to inflate hot air balloons. It is still used to inflate balloons and sophisticated airships for transportation purposes and for travelling experience.
- In Advertising and Entertainment: Helium is used to fill balloons which can be used to advertise various stuffs by printing on the balloons. The balloons are made in various kinds of recognizable shapes and forms which can help to locate different companies or restaurants or circuses etc.
Health Effects on Exposure
- Inhalation: If the helium gas is inhaled in small amounts then it makes the voice sound squeaky, it gives high voice but if concentration of helium inhaled increases then it may cause dullness, headache, dizziness and even suffocation.
- Contact: If liquid helium comes in contact with body parts then it will cause frostbite on that part of the body.
Effects on Surroundings
- On Ventilation: Helium is a very light, non-toxic gas hence if ventilation is good enough then it will escape from the surroundings very rapidly but if ventilation is not good then it will build up in the closed space thus lowering the concentration of oxygen in air. Inhalation of such air mixture will cause problems to humans and animals present in that environment.
References: Helium Element
