Helium

1 · Identity

Symbol, number

He, 2

Oxidation states in water

0 only; a dissolved inert gas with no aqueous chemistry (element entry: no stable compounds, no biological role, not toxic, an asphyxiant only by displacing air).

Note

The element entry carries everything there is to say; this water chapter is deliberately empty.

Sources

Identity

Name and symbol

Helium, He

Atomic number

2 protons

Position

group 18 · period 1 · s-block · noble gas

CAS number

7440-59-7

Atomic structure

Atomic mass

4.002 u

Electron configuration

1s²
1s²

Electrons per shell

2

Valence electrons

2 outer shell

Physical properties

State at room temperature

Gas

Melting point

0.95 K (-272.2 °C)

Boiling point

4.22 K (-268.93 °C)

Density

0.0002 g/cm3 (gas at STP, so 0.1785 g/L)

Appearance

colorless gas, exhibiting a gray, cloudy glow (or reddish-orange if an especially high voltage is used) when placed in an electric field

Thermal conductivity

0.1513 W/(m·K)

Electrical resistivity

not in sources

Electrical conductivity

not in sources

Crystal structure

hexagonal close-packed

Molar heat capacity

not in sources

Chemical properties

Oxidation states

0

Electronegativity

4.16 (Allen Scale)

Ionisation energy

24.587 eV
1st 2,372.3, 2nd 5,250.5 kJ/mol

Electron affinity

0 eV

Atomic radius

empirical 28, covalent 28, van der Waals 140 pm

Ionic radius

not in sources

Reactivity

A noble gas with a closed 1s2 shell and a valence of zero; chemically unreactive under all normal conditions, the least reactive element.

with water

Does not react.

with oxygen, air

Does not react.

with acids

Does not react.

with halogens

Does not react; no stable helium fluoride is known, and helium fluorohydride has been detected only for milliseconds at high pressure and low temperature.

Typical compounds

not in sources

Occurrence, production and use

Crustal abundance

8×10-3 milligrams per kilogram

Oceanic abundance

7×10-6 milligrams per liter

Occurrence and sources

Except for hydrogen, helium is the most abundant element found in the universe. Helium is extracted from natural gas. In fact, all natural gas contains at least trace quantities of helium.

It has been detected spectroscopically in great abundance, especially in the hotter stars, and it is an important component in both the proton-proton reaction and the carbon cycle, which account for the energy of the sun and stars.

The helium content of the atmosphere is about 1 part in 200,000. While it is present in various radioactive minerals as a decay product, the bulk of the Free World's supply is obtained from wells in Texas, Oklahoma, and Kansas. Outside the United States, the only known helium extraction plants, in 1984 were in Eastern Europe (Poland), the USSR, and a few in India.

• helium in natural gas gas fields, up to 7 percent helium; the only commercial source; US recoverable helium in known gas reservoirs estimated at 8,490 million cubic metres (USGS 2021 assessment); other world resources about 31.3 billion cubic metres, chiefly Qatar 10.1, Algeria 8.2, Russia 6.8, Canada 2.0 and China 1.1
• atmospheric helium about 5 ppm by volume, continually escaping to space; not economic to extract
• radiogenic helium alpha decay of uranium and thorium in rocks; the mineral cleveite (uraninite) releases it when dissolved in acid

Extraction, production

Extraction from natural gas and cryogenic purification

Physical separation, no chemical reaction. In 2024 five US plants extracted crude helium (50 to 80 percent) from natural gas and others purified it to Grade-A (99.997 percent) or gaseous helium (above 98 percent); world production about 180 million cubic metres, US sales 81 million cubic metres valued at 1.1 billion dollars (USGS, printed pp. 88 to 89).

Uses

Helium is commercially recovered from natural gas deposits, mostly from Texas, Oklahoma and Kansas. Helium gas is used to inflate blimps, scientific balloons and party balloons. It is used as an inert shield for arc welding, to pressurize the fuel tanks of liquid fueled rockets and in supersonic windtunnels. Helium is combined with oxygen to create a nitrogen free atmosphere for deep sea divers so that they will not suffer from a condition known as nitrogen narcosis. Liquid helium is an important cryogenic material and is used to study superconductivity and to create superconductive magnets. The Department of Energy's Jefferson Lab uses large amounts of liquid helium to operate its superconductive electron accelerator.

Helium is an inert gas and does not easily combine with other elements. There are no known compounds that contain helium, although attempts are being made to produce helium diflouride (HeF2).

▸ as an inert gas shield for arc welding;

▸ a protective gas in growing silicon and germanium crystals and producing titanium and zirconium;

▸ 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. Different ratios of He and O2 are used for different diver operation depths.

Helium is extensively used for filling balloons as it is a much safer gas than hydrogen. One of the recent largest uses for helium has been for pressuring liquid fuel rockets. A Saturn booster, like the type used on the Apollo lunar missions, required about 13 million ft3 of helium for a firing, plus more for checkouts.

Liquid helium's use in magnetic resonance imaging (MRI) continues to increase as the medical profession accepts and develops new uses for the equipment. This equipment has eliminated some need for exploratory surgery by accurately diagnosing patients. Another medical application uses MRE to determine (by blood analysis) whether a patient has any form of cancer.

Helium is also being used to advertise on blimps for various companies, including Goodyear. Other lifting gas applications are being developed by the Navy and Air Force to detect low-flying cruise missiles. Additionally, the Drug Enforcement Agency is using radar-equipped blimps to detect drug smugglers along the United States boarders. In addition, NASA is currently using helium-filled balloons to sample the atmosphere in Antarctica to determine what is depleting the ozone layer.

• Medicine and science: liquid helium cooling of superconducting magnets in MRI scanners and NMR spectrometers; analytical, engineering, laboratory and specialty gases; cooling of the Large Hadron Collider and satellite instruments of US apparent consumption in 2024 (56 million cubic metres): analytical, engineering, lab, science and specialty gases 22 percent; magnetic resonance imaging 17 percent
• Electronics and fibre optics: inert protective atmosphere for growing silicon and germanium crystals, semiconductor fabrication and fibre optics controlled atmospheres, fibre optics and semiconductors, 15 percent of US consumption in 2024
• Metals and aerospace: shield gas for arc welding; pressurising and purging liquid-fuel rockets; leak detection; lifting gas for balloons and airships lifting gas 18 percent, welding 8 percent, aerospace pressurising and purging 7 percent, leak detection 5 percent, diving 5 percent of US consumption in 2024

Safety, toxicity

GHS classification, signal word Warning

• H280 Contains gas under pressure; may explode if heated Gases under pressure
• H281 Contains refrigerated gas; may cause cryogenic burns or injury Gases under pressure

Discovery and name

Discovered by

Norman Lockyer

Discovered

1868

First isolated

William Ramsay, Per Teodor Cleve, Abraham Langlet

Named by

not in sources

Origin of the name

after Helios, Greek god of the Sun

Helium has the lowest melting point of any element and is widely used in cryogenic research because its boiling point is close to absolute zero. Also, the element is vital in the study of super conductivity.

Using liquid helium, Kurti, co-workers and others have succeeded in obtaining temperatures of a few microkelvins by the adiabatic demagnetization of copper nuclei.

Helium has other peculiar properties: It is the only liquid that cannot be solidified by lowering the temperature. It remains liquid down to absolute zero at ordinary pressures, but will readily solidify by increasing the pressure. Solid 3He and 4He are unusual in that both can be changed in volume by more than 30% by applying pressure.

The specific heat of helium gas is unusually high. The density of helium vapor at the normal boiling point is also very high, with the vapor expanding greatly when heated to room temperature. Containers filled with helium gas at 5 to 10 K should be treated as though they contained liquid helium due to the large increase in pressure resulting from warming the gas to room temperature.

While helium normally has a 0 valence, it seems to have a weak tendency to combine with certain other elements. Means of preparing helium difluoride have been studied, and species such as HeNe and the molecular ions He+ and He++ have been investigated.