Helium
Helium is the chemical element with the symbol He and atomic number 2. It is a light, colorless, nonflammable noble gas found in stars, natural gas deposits, balloons, cryogenic systems, MRI magnets, leak detection, welding, and scientific instruments.
What helium is
Helium is a chemical element and noble gas. A helium atom has two protons, and ordinary helium gas consists of individual helium atoms rather than paired molecules like H2 or O2. Helium is colorless, odorless, tasteless, nonflammable, and far less chemically reactive than most elements.
Why helium is a noble gas
Helium has a filled outer electron shell, which makes it very stable and resistant to ordinary chemical bonding. It belongs to Group 18 of the periodic table, the noble gases. This inertness is useful because helium can create protective atmospheres, carry heat, fill spaces, or cool equipment without easily reacting with materials around it.
In stars and the universe
Helium is the second most abundant element in the universe after hydrogen. It formed in the early universe and is also made inside stars by nuclear fusion. In main-sequence stars such as the Sun, hydrogen nuclei fuse into helium, releasing energy. This cosmic abundance contrasts with helium's relative scarcity in Earth's atmosphere.
Where Earth gets helium
On Earth, much usable helium comes from natural gas deposits where helium has accumulated underground. It is produced by radioactive decay of uranium and thorium in rocks, especially as alpha particles that become helium atoms. Because helium is light and can escape Earth's atmosphere into space, recoverable helium is a limited geologic resource.
Liquid helium and cryogenics
Helium becomes liquid only at temperatures close to absolute zero. Liquid helium is valuable for cryogenics because it can cool materials to temperatures that other common refrigerants cannot reach. It is used for superconducting magnets, low-temperature physics, particle accelerators, quantum research, and some space and detector systems.
Medical and industrial uses
Helium is important in MRI machines because many superconducting magnets require very low temperatures. It is also used for leak detection, pressurizing and purging systems, welding shield gas mixtures, deep-sea breathing mixtures, semiconductor manufacturing, fiber-optic production, scientific instruments, and balloons. Balloons are visible, but they are not the highest-value use.
Balloons and buoyancy
Helium balloons float because helium is less dense than air. The surrounding air pushes upward with more force than the combined weight of the balloon and helium inside. Helium is safer than hydrogen for balloons because it does not burn, but balloon use can still waste a resource that is difficult to replace and can create litter or wildlife hazards.
Safety
Helium is not toxic, but it can displace oxygen in enclosed spaces. Inhaling helium from balloons or cylinders can cause oxygen deprivation, and gas from pressurized tanks can injure lungs or airways. Liquid helium can also cause severe cold burns and pressure hazards if trapped liquid warms and expands.
Why it matters
Helium matters because it is simple at the atomic level but hard to replace in many technologies. Its low boiling point, chemical inertness, lightness, and thermal behavior make it valuable for medicine, science, manufacturing, and aerospace. Understanding helium helps explain why a party balloon gas can also be a strategic cryogenic resource.