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Noble Gases and their application in life sciences

Noble Gases and their application
in life sciences
Azad Abdullayev
Baku Higher Oil School
[email protected]
Supervisor: Dos. R.Abbasova
Introduction
The Noble Gases (β€œnoble” means unreactive in chemistry) which were not discovered until
1893 are well known as odorless, colorless and unreactive elements that exist as monoatomic
gases. These remarkable elements belong to the group 18.
The principal source of the noble gases, except for helium, is the atmosphere, where they are
thought to have arisen as by-products of the decay of radioactive elements in the earth’s crust.
In 1893, the English physicist Lord Rayleigh noticed a small incompatibility between the
density of nitrogen obtained by the removal of oxygen, water vapor, and carbon dioxide from
air and the density of nitrogen prepared by chemical reaction, such as the thermal
decomposition of ammonium nitrite:
𝑁𝐻4 𝑁𝑂2 (𝑠) β†’ 𝑁2 (𝑔) + 2𝐻2 𝑂(𝑙)
One liter of nitrogen at 0°C and 1 atm obtained by the removal of all the other known gases
from air has a mass of 1.2572 grams, whereas one liter of dry nitrogen obtained from
ammonium nitrite has a mass of 1.2505 grams under the same conditions. This slight
difference led Lord Rayleigh to suspect that some other gas was present in the sample of
nitrogen from air.
However, this group does have some interesting chemistry and also exhibit interesting
physical properties. Often helium is included as the first member of the group.
Helium (He): πŸπ’”πŸ
Helium is the second lightest element and the second most abundant element in the universe,
after hydrogen. On earth helium is produced from the radioactive decay of Ξ±-emitters (alphaemitters) such as naturally occurring uranium and thorium. Approximately, 3000 metric tons
of helium is formed each year in this way. Naturally occurring helium is trapped in
nonpermeable rock layers beneath the earth. Helium is obtained by separation from natural
gas (which is also trapped in such layers) using fractional distillation. The largest producer of
helium is the United States, which has extensive quantities of helium in its natural gas
deposits.
The speed of sound in helium is nearly three times that in air because of its low atomic mass.
For this reason, if helium is inhaled, say, from a small balloon, it can cause a temporary change
in the fundamental frequency of the vocal cavity, making the voice sound high-pitched.
Neon (Ne): [𝑯𝒆] πŸπ’”πŸ πŸπ’‘πŸ”
Neon is the fifth most abundant element in the universe, but is relatively rare on earth due to
its low mass, which means that, like helium, it also escapes from the upper atmosphere into
space (although at a much slower rate than helium).
Argon (Ar): [𝑡𝒆] πŸ‘π’”πŸ πŸ‘π’‘πŸ”
Argon is the most plentiful and least expensive noble gas. Not considering water vapor, argon
is the third most abundant gas in the earth’s atmosphere. Worldwide, about 700 000 metric
tons of argon are isolated annually from air using fractional distillation. Because it is relatively
inexpensive compared to the other inert gases, argon has a wide variety of industrial uses. It is
used in fluorescent and incandescent light bulbs because it does not react with the discharge
electrodes or the hot filament.
Krypton (Kr): [𝑨𝒓] πŸ‘π’…πŸπŸŽ πŸ’π’”πŸ πŸ’π’‘πŸ”
Krypton is also very unreactive but costly element. Some clathrate compounds occur –
compounds in which krypton atoms are sandwiched or caged in by other molecules without
forming any definite chemical bonds with the encaging molecules. For example, 3𝐢6 𝐻4 (𝑂𝐻)2 βˆ—
0.74πΎπ‘Ÿ in which some krypton atoms become trapped inside crystals of 𝐢6 𝐻4 (𝑂𝐻)2 .
Xenon (Xe): [𝑲𝒓] πŸ’π’…πŸπŸŽ πŸ“π’”πŸ πŸ“π’‘πŸ”
Xenon has quite a rich chemistry, forming a variety of compounds with the most reactive
elements, such as fluorine and oxygen. These compounds are unstable, often explosive and
producing hazardous products such as HF. It reacts by expanding its octet. The fluorides are
stable colorless/white solids at room temperature. Even with fluorine, reactions are reluctant
and require harsh conditions and a catalyst:
𝑿𝒆(π’ˆ) + π‘­πŸ (π’ˆ) β†’ π‘Ώπ’†π‘­πŸ (𝒔) (Xenon difluoride)
1:4 ratio of 𝑿𝒆: π‘­πŸ , passed through a Ni tube at πŸ’πŸŽπŸŽπ’ π‘ͺ
𝑿𝒆(π’ˆ) + πŸπ‘­πŸ (π’ˆ) β†’ π‘Ώπ’†π‘­πŸ’ (𝒔) (Xenon tetrafluoride)
1:5 ratio of 𝑿𝒆: π‘­πŸ , heated for 1h at 13 atm in a Ni can at πŸ’πŸŽπŸŽπ’ π‘ͺ
𝑿𝒆(π’ˆ) + πŸ‘π‘­πŸ (π’ˆ) β†’ π‘Ώπ’†π‘­πŸ” (𝒔) (Xenon hexafluoride)
Heated 𝑿𝒆 in excess π‘­πŸ at 200 atm
In these structures Xenon has expanded its octet to accommodate more electrons.
The fluorides all react with water, splitting the water molecules (hydrolysis):
𝟏
π‘Ώπ’†π‘­πŸ (𝒔) + π‘―πŸ 𝑢(𝒍) β†’ 𝑿𝒆(π’ˆ) + π‘ΆπŸ (π’ˆ) + πŸπ‘―π‘­(𝒂𝒒/π’ˆ)
𝟐
𝟏
πŸπ‘Ώπ’†π‘­πŸ’ (𝒔) + πŸ’π‘―πŸ 𝑢(𝒍) β†’ 𝑿𝒆(π’ˆ) + π‘ΆπŸ (π’ˆ) + π‘Ώπ’†π‘ΆπŸ‘ + πŸ–π‘―π‘­(𝒂𝒒/π’ˆ)
𝟐
π‘Ώπ’†π‘­πŸ” (𝒔) + π‘―πŸ 𝑢(𝒍) β†’ π‘Ώπ’†π‘Άπ‘­πŸ’ + πŸπ‘―π‘­(𝒂𝒒/π’ˆ)
π‘Ώπ’†π‘­πŸ” (𝒔) + πŸ‘π‘―πŸ 𝑢(𝒍) β†’ π‘Ώπ’†π‘ΆπŸ‘ + πŸ”π‘―π‘­(𝒂𝒒/π’ˆ)
The fluorides are all strong oxidizing and fluorinating reagents:
π‘Ώπ’†π‘­πŸ’ (𝒔) + πŸ’π‘²π‘° β†’ 𝑿𝒆(π’ˆ) + πŸπ‘°πŸ (𝒔) + πŸ’π‘²π‘­(𝒔)
π‘Ώπ’†π‘­πŸ’ (𝒔) + 𝑷𝒕(𝒔) β†’ 𝑿𝒆(π’ˆ) + π‘·π’•π‘­πŸ’
π‘Ώπ’†π‘­πŸ’ (𝒔) + πŸπ‘Ίπ‘­πŸ’ β†’ 𝑿𝒆 + πŸπ‘Ίπ‘­πŸ”
Xenon trioxide (π‘Ώπ’†π‘ΆπŸ‘ βˆ’ a colorless/white crystalline solid) is produced by hydrolysis of
π‘Ώπ’†π‘­πŸ’ or π‘Ώπ’†π‘­πŸ” :
𝟏
πŸπ‘Ώπ’†π‘­πŸ’ (𝒔) + πŸ’π‘―πŸ 𝑢(𝒍) β†’ 𝑿𝒆(π’ˆ) + π‘ΆπŸ (π’ˆ) + π‘Ώπ’†π‘ΆπŸ‘ + πŸ–π‘―π‘­(𝒂𝒒/π’ˆ)
𝟐
π‘Ώπ’†π‘­πŸ” (𝒔) + πŸ‘π‘―πŸ 𝑢(𝒍) β†’ π‘Ώπ’†π‘ΆπŸ‘ + πŸ”π‘―π‘­(𝒂𝒒/π’ˆ)
π‘Ώπ’†π‘ΆπŸ‘ reacts with water to form xenon hydroxide:
π‘Ώπ’†π‘ΆπŸ‘ + πŸ‘π‘―πŸ 𝑢 ↔ 𝑿𝒆(𝑢𝑯)πŸ”
π‘Ώπ’†π‘Άπ‘­πŸ’ (Xenon oxytetrafluoride) is a colorless liquid and is produced by hydrolysis of π‘Ώπ’†π‘­πŸ”
:
π‘Ώπ’†π‘­πŸ” (𝒔) + π‘―πŸ 𝑢(𝒍) β†’ π‘Ώπ’†π‘Άπ‘­πŸ’ + πŸπ‘―π‘­(𝒂𝒒/π’ˆ)
π‘Ώπ’†π‘Άπ‘­πŸ’ (Xenon oxyfluoride) is also formed by hydrolysis of π‘Ώπ’†π‘Άπ‘­πŸ’ at low temperature:
π‘Ώπ’†π‘­πŸ’ (𝒔) + π‘―πŸ 𝑢(𝒍) β†’ π‘Ώπ’†π‘Άπ‘­πŸ + πŸπ‘―π‘­(𝒂𝒒/π’ˆ)
Radon (Rn): [𝑿𝒆] πŸ“π’…πŸπŸŽ πŸ”π’”πŸ πŸ”π’‘πŸ”
Radon is a naturally occurring, radioactive noble gas formed in the radioactive decay of
radium-226, which in turn arises from the radioactive decay of uranium ores. Because it is
radioactive and inert, radon sees few commercial or academic uses. However, it is a major
health hazard.
The Application of Noble Gases
Helium is used in lighter-than-air aircraft because it is nonflammable. It is also used in
welding to provide an inert atmosphere around the welding flame and thus reduce corrosion
of the heated metal. An inert helium environment is used for growing silicon and germanium
crystals in the semiconductor industry. Helium is used as an inert carrier gas in gas
chromatography (an analytical method used to separate mixtures). It is also used to replace
nitrogen in deep-sea-diving breathing mixtures to help reduce the formation of nitrogen
bubbles in the blood, a condition known as the bends.
Neon is used in neon signs, which are essentially discharge tubes filled with neon or a gas
mixture containing neon. Neon has traditionally been used in a variety of electronics such as
vacuum tubes and television tubes and in some cryogenic applications. Neon is also used in
helium-neon lasers, which operated as bar-code scanners and optical disk readers before the
development of less costly diode lasers.
Argon is used to provide an inert atmosphere in welding; in sealed museum cases to help
preserve specimens that are subject to oxidation in air; in special fire extinguishers; for
growing silicon and germanium crystals; and to fill the space above wines and
pharmaceuticals to prevent oxidation. The gas is also used in argon lasers, which are used
predominantly in laser surgery.
Krypton and Xenon are used in lasers, flashtubes for high-speed photography, and
automobile-engine timing lights. Xenon arc lamps produce an intense white light and are used
in applications such as IMAX projectors and high-intensity headlights. Xenon is also used as a
propellant in ion thrusters on spacecraft. In the early 1940s it was discovered that xenon gas
could be used as a general anesthetic, although its medical use has been limited to date.
Discharge color
When an electric discharge is passed through a noble gas, light is emitted as electronically
excited noble-gas atoms decay to lower energy levels. The color of gas discharge emission
depends on several factors, including the following:
ο‚· Discharge parameters (local value of current density and electric field, temperature,
etc.);
ο‚· Gas purity (even small fraction of certain gases can affect color);
ο‚· Material of the discharge tube envelope.

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