Characteristics of helium
Helium, of symbol He in the periodic table, is a noble and inert (it doesn’t react with any other element) gas in all standard conditions. Helium has atomic number 2, that to say, it has 2 protons and 2 electrons. This makes it the second lightest element in the universe, only surpassed by hydrogen, with only a proton and an electron.
Colourless, odourless and tasteless, helium has the lowest boiling and freezing points of any other known substance. It becomes liquid at a temperature of 4.25 degrees Kelvin (-268 ºC), and it can’t be solidified by lowering the temperature. It maintains liquid until de absolute zero in standard conditions, but it solidifies by increasing the pressure. It is necessary to apply to it a pressure of 25 atmospheres and a temperature of one Kelvin (-272 ºC) to convert it to its solid state.
Helium isn’t toxic at all, even if an excessive inhalation of this gas can be dangerous, as it acts as asphyxiating.
Abundance in the universe and formation
Helium is the second most common element in the universe, representing approximately 9% of the latter, only surpassed by hydrogen, which constitutes 90% of our universe. These two elements come from the Big Bang. Nowadays helium is produced in big quantities in the nucleus of stars, using the nuclear fusion
Even if it is very abundant in the universe, helium is scarce on Earth. Its content in the atmosphere is only 5 ppm (parts per million). On the Earth, there is a constant production of helium (through the radioactive decay of some elements), but it readily escapes from the terrestrial atmosphere due to its lightness. Approximately 3000 tonnes of helium are produced annually in the lithosphere, even if they escape quickly to space.
History and discovery
In 1968, the French astronomer Pierre Janssen travelled to India to measure the solar spectrum during a total eclipse and observed a new yellow spectral line that indicated a new element. The astronomer Joseph Norman Lockyer obtained the same results by observing the Sun, through London’s smog, and assuming that this new element was a metal, he named it helium. However, it wasn’t until 1895 that this element was isolated for the first time, by William Ramsay.
The name helium comes from Helios, the name of the Greek god of the Sun.
Uses of this element
Helium is recovered, for commercial use, from the deposits of natural gas, mainly in Texas. The unique properties that offer this element make it a very good election for a bug variety of uses. These are some of the diverse uses which are given to helium:
- As helium in the liquid state is the coldest substance to exist, the latter is used as a cooling medium for the Large Hadron Collider (LHC) and for the superconductive magnets in the magnetic resonance imaging systems. It is also used for maintaining the instruments in a satellite cool.
- Helium is also used as a coolant in nuclear reactors, and it maintains cool the propellant of a rocket during launch.
- Thanks to its low density, helium is the ideal option to blow up party and meteorological balloons, as well as airships. Hydrogen was previously used for this purpose, but being this element highly flammable, it is no longer used.
- As helium is an element that doesn’t react with any material, it is an excellent option to provide a protective atmosphere in the fabrication of fibre optics and semiconductors.
- A mix of 80% helium and 20% oxygen is used as an artificial atmosphere for deep-sea divers.
Of the eight known isotopes of helium, only two of them are stable: helium-3 (3He) and helium-4 (4He). Of these two isotopes, helium-3 is the most unusual: in the Earth’s atmosphere there is an atom of 3He for a million atoms of 4He. Helium-4 is produced on the Earth via the alpha disintegration of radioactive elements such as uranium. However, helium-3, much more scarce on Earth, is produced via the beta disintegration of tritium (an isotope of hydrogen). Helium-3 is very valuable, as it is scarce, and it is planned to use it in the future as fuel for nuclear fusion to produce energy. This isotope is found in bigger concentrations in the interstellar medium and the lunar surface.
Helium has other isotopes, manufactured artificially, which are 5He, 6He, 7He, 8He, 9He, and 10He. Nevertheless, these isotopes are extremely unstable. Some of these isotopes disintegrate in other isotopes of helium, which at the same time disintegrate in other elements.