He
HELIUM
(Gr. hellos, the sun)
He at. wt. 1.0026
at. no. 2
b.p. -268.6° C
density 0.1785 gm/l (0° C, 1 atm.)
liquid density 7.62 lb/cu. ft. at b.p.
valence usually 0
Electronic configuration
| SHELL |
K |
L |
M |
N |
O |
P |
Q |
| SUB SHELL |
He |
Neon |
Argon |
Krypton |
Xenon |
Radon |
Eka-radon |
| 1s |
2s 2p |
3s 3p |
3d 4s 4p |
4d 5s 5p |
4f 5d 6s 6p |
5f 6d 7s 7p |
| Helium
|
1s2 |
|
|
|
|
|
|
| Symbol
|
1S0 |
Helium. Evidence of the existence of helium
was first obtained by Janssen 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 Ramsay discovered helium in the
uranium mineral clevite, and it was independently discovered
in clevite by the Swedish chemists Cleve and Langlet about
the same time. Rutherford and Royds in 1907 demonstrated that a particles are helium nuclei. Except for hydrogen, helium is the most abundant element found throughout
the universe. 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 accounts 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 I 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 rexas,
Oklahoma, and Kansas. The only helium plant in the Free
World outside the U.S. is near Swift River, Saskatchewan.
The cost of helium fell from $2500/cu. ft. in 1915 to 1.5
cent/cu. ft. in 1940. The U.S. Bureau of Mines has set the
price of Grade A helium at $35/1000 cu. ft. Helium has the
lowest m.p. of any element and has found wide use in cryogenic research as its b.p. is close to absolute zero. Its use in
the study of superconductivity is vital. Using liquid helium,
Kurti and co-workers, and others, have succeeded in
obtaining temperatures of a few microdegrees Kelvin, by
the adiabatic demagnetization of copper nuclei, starting
from about 0.010K. Five isotopes of helium are known. Liquid helium (He4) exists in two forms: He4 I and He4 II,
with a sharp transition point at 2.1740K (3.83cm Hg).
He4 I (above this temperature) is a normal liquid, but He4 II
(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 obey normal rules.
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 He3 and He4 are unusual in that both can readily be
changed in volume by more than 30% by application of
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 100K 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 are being studied, and species, such as
HeNe and the molecular ions Her and Het + have been
investigated. Helium is widely used as an inert gas shield
for arc welding; as a protective gas in growing silicon and
germanium crystals, and in titanium and zirconium production; as a cooling medium for nuclear reactors; and as'
a gas for supersonic wind tunnels. A mixture of 80%
helium and 20% oxyg'en is used as an artificial atmosphere
for divers and others wbrking under pressure. Helium is
extensively used for filling balloons as it is a much safer gas
than hydrogen. While its density is almost twice that of
hydrogen, it has about 98% of the lifting power of hydrogen.
At sea level, 1000 cu. ft. of helium lifts 68.5 lb. One of the
recent largest uses for helium has been for pressuring liquid
fuel rockets. A Saturn booster, such as used on the Apollo
lunar missions, requires about 13 million cubic feet of
helium for a firing, plus more for checkouts.
© 1999 F. Davies
Delphi O.E.M. Co.
All rights reserved
