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Helium is the second element on the periodic table, with atomic number 2 and element symbol He. It's the lightest noble gas. Here are ten quick facts about the element helium. Check the full listing for helium if you would like additional element facts.
- The atomic number of helium is 2, meaning each atom of helium has two protons. The most abundant isotope of the element has 2 neutrons. It is energetically favorable for each helium atom to have 2 electrons, which gives it a stable electron shell.
- Helium has the lowest melting point and boiling point of the elements, so it only exists as a gas, except under extreme conditions. At normal pressure, helium is a liquid at absolute zero. It must be pressurized to become a solid.
- Helium is the second-lightest element. The lightest element or one with the lowest density is hydrogen. Even though hydrogen typically exists as a diatomic gas, consisting of two atoms bonded together, a single atom of helium has a higher density value. This is because the most common isotope of hydrogen has one proton and no neutrons, while each helium atom typically has two neutrons as well as two protons.
- Helium is the second-most abundant element in the universe (after hydrogen), though it is much less common on Earth. On Earth, the element is considered a nonrenewable resource. Helium does not form compounds with other elements, while the free atom is light enough to escape Earth's gravity and bleed out through the atmosphere. Some scientists are concerned we might one day run out of helium or at least make it prohibitively expensive to isolate.
- Helium is colorless, odorless, tasteless, non-toxic, and inert. Of all the elements, helium is the least reactive, so it does not form compounds under ordinary conditions. In order to bond it to another element, it would need to be ionized or pressurized. Under high pressure, disodium helide (HeNa2), the clathrate-like titanate La2/3-xLi3xTiO3He, the silicate crystobalite He II (SiO2He), dihelium arsenolite (AsO6·2He), and NeHe2 may exist.
- Most helium is obtained by extracting it from natural gas. Its uses include helium party balloons, as a protective inert atmosphere for chemistry storage and reactions, and for cooling superconducting magnets for NMR spectrometers and MRI machines.
- Helium is the second-least reactive noble gas (after neon). It is considered the real gas that most closely approximates the behavior of an ideal gas.
- Helium is monatomic under standard conditions. In other words, helium is found as single atoms of the element.
- Inhaling helium temporarily changes the sound of a person's voice. Although many people think inhaling helium makes a voice sound higher, it doesn't actually alter the pitch. Though helium is non-toxic, breathing it can result in asphyxiation due to oxygen deprivation.
- Evidence of helium's existence came from the observation of a yellow spectral line from the sun. The name for the element comes from the Greek god of the Sun, Helios.