Helium

hydrogen ← helium → lithium - ↑ He ↓ Ne 2He Periodic table
Appearance
colorless gas, exhibiting a red-orange glow when placed in a high-voltage electric field Spectral lines of helium
General properties
Name, symbol, number	helium, He, 2
Pronunciation	/ˈhiːliəm/ HEE-lee-əm
Element category	noble gases
Group, period, block	18, 1, s
Standard atomic weight	4.002602(2) g/mol
Electron configuration	1s2
Electrons per shell	2 (Image)
Physical properties
Phase	gas
Density	(0 °C, 101.325 kPa) 0.1786 g/L
Liquid density at m.p.	0.145 g/cm3
Liquid density at b.p.	0.125 g/cm3
Melting point	(at 2.5 MPa) 0.95 K, −272.20 °C, −457.96 °F
Boiling point	4.22 K, −268.93 °C, −452.07 °F
Critical point	5.19 K, 0.227 MPa
Heat of fusion	0.0138 kJ/mol
Heat of vaporization	0.0829 kJ/mol
Specific heat capacity	(25 °C) 5R/2 = 20.786 J/(mol·K)
Vapor pressure (defined by ITS-90)
P (Pa) 1 10 100 1 k 10 k 100 k at T (K)     1.23 1.67 2.48 4.21
Atomic properties
Oxidation states	0
Electronegativity	no data (Pauling scale)
Ionization energies	1st: 2372.3 kJ/mol
	2nd: 5250.5 kJ/mol
Covalent radius	28 pm
Van der Waals radius	140 pm
Miscellanea
Crystal structure	hexagonal close-packed
Magnetic ordering	diamagnetic
Thermal conductivity	(300 K) 0.1513 W/(m·K)
Speed of sound	972 m/s
CAS registry number	7440-59-7
Most stable isotopes
Main article: Isotopes of helium
iso NA half-life DM DE (MeV) DP 3He 0.000137%* 3He is stable with 1 neutron 4He 99.999863%* 4He is stable with 2 neutrons *Atmospheric value, abundance may differ elsewhere.

Because it is very light, helium is the gas of choice to fill airships such as the Goodyear blimp

Helium is a chemical element. It has the chemical symbol He, atomic number 2, and atomic weight of about 4.002602. There are 9 isotopes of helium, only two of which are stable. These are ³He and ⁴He. ⁴He is by far the most common isotope.

Helium is called a noble gas, because it does not regularly mix with other chemicals and form new compounds. It has the lowest boiling point of all the elements. It is the second most common element in the universe, after hydrogen, and has no color or smell. However, Helium has a blue-ish, neon color when being burnt with fire. Helium does not usually react with anything else. Astronomers discovered helium in 1868. They found that it was in the Sun before it was found on Earth. Because of where it was found, its name comes from the Greek word for Sun, helios.

Helium is used to fill balloons and airships because it is lighter than air, and does not burn or react, meaning it is normally safe for using it in that way. It is also used in some kinds of light bulbs. People also breathe it in to make their voices sound higher than they normally do as a joke, but this is extremely dangerous as if they breathe in too much, it can kill them as they are not breathing normal air. Breathing too much helium can also cause long-term effects to vocal cords.

It can be created through the process of nuclear fusion in the sun. During this process, four Hydrogen atoms are fused together to form one helium atom.

Supply

Helium has become a rare gas. If it gets free into the air it leaves the planet. Unlike hydrogen, which reacts with oxygen to form water, helium is not reactive. It stays as a gas. For many years the USA kept a storage tank filled with helium which came naturally from the great plains area. The story of this supply is very complicated. At present, more helium is supplied by Qatar than by the USA.

Several research organisations have released statements on the scarcity and conservation of helium. These organisations released policy recommendations as early as 1995 and as late as 2016 urging the United States government to store and conserve helium because of the natural limits to the helium supply and the unique nature of the element. For researchers, helium is irreplaceable because it is essential for producing very low temperatures.