Helium

Helium (chemical symbol He) is a chemical element with atomic number 2. The atomic number indicates the number of protons in an atom's nucleus. Helium belongs to the group of noble gases, which are gases that do not readily react with other elements. Under normal conditions it is a colorless, odorless, and tasteless gas.

Helium is the second lightest and second most abundant element in the universe, after hydrogen. Most of the helium in the universe originates from the early stages of the universe and from nuclear fusion occurring in the cores of stars. On Earth, helium is scarce because its atoms are light and escape Earth's gravity, so the atmosphere does not retain it.

Physical properties

Helium has the lowest melting point of all elements; it becomes liquid only at temperatures very close to absolute zero (and does not solidify under normal pressure). For this reason it is used in cryogenics, the study of very low temperatures. Liquid helium exhibits a property called superfluidity: at very low temperatures, the liquid flows without measurable viscosity.

Extraction and production

Commercial helium is mostly extracted from natural gas found underground. In some locations, natural gas contains helium that can be separated using cooling and fractional distillation based on boiling points. The primary source of helium beneath Earth's surface is radioactive decay of heavy elements such as uranium and thorium, which produce alpha particles that transform into helium atoms.

Applications

Helium is used to fill balloons and light aircraft because it is lighter than air and does not burn like hydrogen. It is also used to cool the superconducting magnets in medical imaging machines (MRI), as a protective gas in welding to shield the work area, and in leak detection in pipes. Some deep-sea divers use helium in their breathing mixtures to reduce the effects of nitrogen narcosis.