a gas whose name is
the Greek word for "inactive"
atomic mass 39.948 amu
-189.35 °C (-308.83 °F)
boiling point -185.7 °C (-302.53
Argon is colorless
and odorless in both liquid and gaseous forms.
Making up about 1% of the
atmosphere, argon is the third most abundant gas
on Earth. The vast majority of argon on
Earth comes from the radioactive decay of
potassium-40, which produces stable argon-40.
Not found in any compounds,
pure argon is isolated through liquid air
fractionation. Over 750 tons of argon are
produced every year.
Because argon is chemically
inert, it is used in a number of devices and
applications that require a non-reactive
atmosphere. It is the gas that protects the
filament inside most lightbulbs from premature
failure, and, because it does not conduct heat or
cold very well, also fills the gap(s) between
panes in double- and triple-pane windows. Its
non-reactive property makes it ideally suited as
an inert gas shield in arc welding and cutting,
as a non-reactive blanket in the manufacture of
titanium and other reactive elements, and as a
protective atmosphere for growing silicon and
Most people are familiar with carbon dating,
which uses the decay of the radioactive carbon-14
isotope to find the ages of things that were once
alive. But, because carbon-14's half-life is
about 5,730 years, the technique is not useful
for material more than about 60 thousand years
old. Potassium-argon dating allow us to date
rocks that are much older than this. Potassium-40
decays to argon-40 and calcium-40, with a
half-life of 1.25 billion years. The ratio of
potassium-40 to argon-40 trapped in rock can be
used to determine how long it has been since the
rock has solidified.
The first Noble Gas to be discovered,
argon's presence was first suspected by Henry Cavendish
in 1785, but it was not isolated until Lord
Rayleigh and Sir William Ramsay did so in 1894.
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