He

He

He is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table. Its boiling and melting points are the lowest among all the elements.

History

Helium was first detected in the solar spectrum by Jules Janssen and Norman Lockyer in 1868. It was later isolated on Earth by William Ramsay, Per Teodor Cleve, and Nils Abraham Langlet in 1895.

Properties

Helium is the second lightest and second most abundant element in the observable universe, being present in about 24% of the total elemental mass, which is more than 12 times the mass of all the heavier elements combined. Its abundance is due to the very high nuclear binding energy (per nucleon) of helium-4, with respect to the next three elements after helium. This helium-4 binding energy also accounts for why it is a product of both nuclear fusion and radioactive decay.

Isotopes

There are two stable isotopes of helium: helium-3 and helium-4. Helium-4 is by far the most common, making up about 99.99986% of the helium on Earth. Helium-3 is much rarer and is sought after for use in cryogenics and nuclear fusion research.

Applications

Helium has many applications, including in cryogenics, particularly in the cooling of superconducting magnets, such as those used in magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) spectrometers. It is also used as a protective gas in arc welding, in the production of semiconductors, and as a lifting gas in balloons and airships.

Occurrence

Helium is found in large amounts in natural gas fields, particularly in the United States, which is the world's largest supplier. It is extracted through a process of fractional distillation.

Safety

Helium is non-toxic and inert, making it safe to use in many applications. However, inhaling helium can be dangerous as it can displace oxygen needed for normal respiration.

See also

• Noble gas
• Periodic table
• Cryogenics
• Nuclear fusion
• Magnetic resonance imaging
• Arc welding

External links

Template:Periodic table

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