| Atomic Number: | 2 | Atomic Symbol: | He |
| Atomic Weight: | 4.00260 | Electron Configuration: | 2 |
| Shells: | 2 | Filling Orbital: | 1s2 |
| Melting Point: | -272oC @ 26atm. | Boiling Point: | -268.6oC |
| Uses: | Blimps, ballons, deep sea diving, welding etc. |
History
(Gr. helios, the sun). Janssen obtained the first evidence of
helium during the solar eclipse of 1868 when he detected a new line in the solar
spectrum. Lockyer and Frankland suggested the name helium for the new element.
In 1895 Sir William Ramsay in Scotland discovered helium in the uranium mineral
clevite while it was independently discovered in cleveite by the Swedish
chemists P.T. Cleve and Nils Langlet at about the same time.
Rutherford and Royds in 1907 demonstrated that alpha particles are helium
nuclei.
Sources
Except for hydrogen, helium is the most
abundant element found through out 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 fusion of hydrogen into helium provides the energy of the hydrogen bomb.
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. The only
known helium extraction plants, outside the United States, in 1984 were in
Eastern Europe (Poland), the U.S.S.R., and a few in India.
Cost
The cost of helium fell from $2500/ft3 in 1915 to 1.5
cents /ft3 in 1940. The U.S. Bureau of Mines has set the price of
Grade A helium at $37.50/1000 ft3 in 1986.
Properties
Helium has the lowest melting point of any element and is
widely used in cryrogenic research because its boiling point is close to
absolute zero. Also, the element is vital in the study of superconductivity.
Using liquid helium, Kurti and co-workers and others, have succeeded in
obtaining temperatures of a few microkelvins by the adiabatic demagnetization of
copper nuclei.
It has other peculiar properties. Helium is the only liquid that cannot be
solidified by lowering the temperature. It remains liquid down to absolute zero
at ordinary pressures, but it can readily be solidified 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 diflouride have
been studied, and species such as HeNe and the molecular ions He+ and He++ have
been investigated.
Isotopes
Seven isotopes of helium are known: Liquid helium (He4) exists
in two forms: He4I and He4II, with a sharp transition point at 2.174K. He4I
(above this temperature) is a normal liquid, but He4II (below it) is unlike any
other known substance. It expands on cooling; its conductivity for heat is
enormous; and neither its heat conduction nor viscosity obeys normal rules.
Uses
- as an inert gas shield for arc welding;
- a protective gas in growing silicon and germanium crystals and producing
titatium 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/O2 are used for different depths at which the
diver is operating.
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.
Costs
Materials which become superconductive at higher temperatures than
the boiling point of helium could have a major impact on the demand for helium.
These less costly refrigerant materials could replace the present need to cool
superconductive materials to the boiling point of helium.