Helium Facts (Atomic Number 2 or He)

Chemical & Physical Properties of Helium

A helium filled discharge tube shaped like the element's atomic symbol.
A helium filled discharge tube shaped like the element's atomic symbol. pslawinski, metal-halide.net

Helium is atomic number 2 on the periodic table, with the element symbol He. It is a colorless, flavorless gas, best known for its use in filling floating balloons. Here is a collection of facts about this lightweight, interesting element:

Helium Element Facts

Helium Atomic Number: 2

Helium Atomic Weight: 4.002602(2)


Helium Electron Configuration: 1s2

Word Origin: Greek: helios, sun. Helium was first detected as a new spectral line during a solar eclipse, so it is named for the Greek Titan of the Sun.

Isotopes: 9 isotopes of helium are known. Only two isotopes are stable: helium-3 and helium-4. While the isotopic abundance of helium varies depending on geographical location and source, 4He accounts for nearly all of the natural helium.


Uses: Helium is widely used in cryogenic research because its boiling point is near absolute zero. It is used in the study of superconductivity, as an inert gas shield for arc welding, as a protective gas in growing silicon and germanium crystals and producing titanium and zirconium, for pressuring liquid fuel rockets, for use in magnetic resonance imaging (MRI), as a cooling medium for nuclear reactors, and as a gas for supersonic wind tunnels. A mixture of helium and oxygen is used as an artificial atmosphere for divers and others working under pressure. Helium is used for filling balloons and blimps.

Sources: Except for hydrogen, helium is the most abundant element in the universe. It is an important component in the proton-proton reaction and the carbon cycle, which account for the energy of the sun and stars. Helium is extracted from natural gas. In fact, all natural gas contains at least trace quantities of helium. The fusion of hydrogen into helium is the sources of a hydrogen bomb's energy. Helium is a disintegration product of radioactive substances, so it is found in ores of uranium, radium, and other elements. Most of Earth's helium dates back to the planet's formation, although a small amount falls to Earth within cosmic dust and some is produced via beta decay of tritium.

Health Effects: Helium serves no biological function. Trace amounts of the element are found in human blood. While helium is considered to be non-toxic, it displaces oxygen so inhaling it can lead to hypoxia or asphyxiation. Fatalities from inhaling helium are rare. Liquid helium is a cryogenic liquid, so risks include frostbite from exposure and explosion from expansion if the liquid is stored in a sealed container. The mixture of helium and oxygen (heliox) can cause high-pressure nervous syndrome, however the addition of nitrogen can remedy the issue.

Compounds: Because a helium atom has a valence of zero, it has extremely low chemical reactivity. However, unstable compounds called excimers can be formed when electricity is applied to the gas. HeH+ is stable in its ground state, but it is the strongest known Bronsted acid, capable of protonating any species it encounters. Van der Waals compounds form with cryogenic helium gas, such as LiHe.

Element Classification: Noble Gas or Inert Gas

Usual Phase: gas

Density (g/cc): 0.1786 g/L (0 °C, 101.325 kPa)

Liquid Density (g/cc): 0.125 g/mL (at its boiling point)

Melting Point (°K): 0.95

Boiling Point (°K): 4.216

Critical Point: 5.19 K, 0.227 MPa

Atomic Volume (cc/mol): 31.8

Specific Heat (@20°C J/g mol): 5.188

Heat of Fusion: 0.0138 kJ/mol

Evaporation Heat (kJ/mol): 0.08

First Ionizing Energy (kJ/mol): 2361.3

Lattice Structure: Hexagonal

Lattice Constant (Å): 3.570

Lattice C/A Ratio: 1.633

Crystal Structure: close-packed hexagonal

Magnetic Ordering: diamagnetic

CAS registry number: 7440-59-7

Quiz: Ready to test your helium facts knowledge? Take the Helium Facts Quiz.


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