# Xenon (Xe): Properties & Uses

It took scientists more than a hundred years to completely understand the composition of the air. Xenon was discovered in 1898 by Scottish chemist and physicist, Sir William Ramsay (1852-1916), and English chemist Morris William Travers (1872-1961). Ramsay and Travers used liquid air to make their discovery. After they discovered that this gas does not react much with any other compound, they classified it as a noble gas along with krypton and neon. Like other chemical elements, the name xenon has also been originated from the Greek word “Xenos,” which means stranger or a foreigner, and it is pronounced as “ZEE-non.”

Xenon, symbolized by (Xe), is an element with atomic no. 54 and atomic weight 131.293 u. It belongs to the noble gases group of the periodic table of elements. Like other noble gas elements, xenon is also generally non-reactive, but it tends to form a few chemical compounds. It took scientists to do lengthy research and experimentation on noble gases to discover xenon. One can say that it was almost accidental. Much heavier than neon and krypton, it had not been explicitly predicted and was sufficiently rare to avoid chance detection. Its extreme rareness in nature and relatively heavy density which was unusual for a common experience, and therefore, it was named Xenon, a ‘foreign’ gas.

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## Occurrence

Xenon is a rare trace gas found in the earth’s atmosphere, approximately 1 part per 11.5 million. It can also be found in some of the extracted minerals from the earth. Commercially, it is produced as a by-product of fractional distillation of liquid air. Even the liquid oxygen extracted from fractional distillation has small traces of krypton and xenon. Its abundance in our solar system is also exceptional, approximately 1 in 630 thousand parts by mass. Jupiter has the highest amount of Xenon in its atmosphere, around 2.6 times its abundance on the Sun. The reason for low territorial xenon on Earth can be explained by the covalent bonding of xenon and oxygen within Quartz, which can trap xenon from escaping into the atmosphere. Unlike other noble gases, xenon can not be produced by stellar nucleosynthesis, as it takes an intense amount of nuclear fusion energy to produce elements beyond iron in the stars. However, other cosmic events such as supernova explosions and nova explosions can form xenon by slow neutron capture process (s-process) in red giants that have entered Asymptotic Gaint Branch (AGB).

It can also be formed by the radioactive decay of iodine-129, and spontaneous fission of heavy elements such as thorium, uranium, and plutonium.

## Isotopes

Xenon naturally occurs in nine isotopes out of which seven are stable and two are radioactive. _{ }^{ 126 }{ X }e, _{ }^{ 128 }{ X }e, _{ }^{ 129 }{ X }e, _{ }^{ 131 }{ X }e, _{ }^{ 132 }{ X }e, and _{ }^{ 133 }{ X }e are stable, whereas _{ }^{ 124 }{ X }e and _{ }^{ 134 }{ X }e are the two radioactive and very long-lived isotopes of xenon with a half-life of  1.8 * { 10 }^{ 22 } years and 2.1 × { 10 }^{ 21 } years, respectively. Additionally, there are 38 other radioactive isotopes of Xenon. _{ }^{ 124 }{ X }e and _{ }^{ 134 }{ X }e are known to be created after a few seconds of the Big Bang, and they underwent the process of double beta decay. Some radioactive isotopes of xenon, e.g., _{ }^{ 133 }{ X }e and _{ }^{ 135 }{ X }e, are produced by neutron irradiation of fissionable material within nuclear reactors.

## Properties of Xenon

### Physical Properties

At standard temperature and pressure conditions, xenon appears as colourless, odourless, and tasteless gas, with a gas density of around 5.761 kilograms per cubic meter, which is 4.5 times the density of air. In a discharge tube, xenon, when treated under an electric potential, emits a spectrum of visible light mostly concentrated in the blue region. At the temperature of  -108.13°C, xenon changes from a gas to a liquid, with a liquid density of 3.1 gram per millilitre.

Solid and liquid xenon at its triple point temperature

Due to its large atomic volume as a liquid, xenon is highly polarizable, and therefore, provides higher solubility and acts as an excellent solvent. It can dissolve many hydrocarbons, biomolecules, and even water. Xenon changes its phase from liquid to solid at a temperature of -111.5°C, with a density of  3.640 grams per cubic centimetre. If we increase the pressure to around 150 gigapascals, it can even transform into a metallic state. Solid Xenon has a face cubic centred structure, but it starts to change to hexagonal close-packing as we increase the pressure. Due to the relatively small width of metallic Xenon, it absorbs red light and emits blue light, which is unusual in metals.

Phase Diagram of Xenon

### Chemical Properties

Xenon has an electronic configuration [Kr] 4{ d }^{ 10 }5{ s }^{ 2 }5{ p }^{ 6 }. For a long time, like other noble gases, xenon was also thought to be chemically non-reactive. But after the discovery of xenon platinofluoride ({ XePtF }_{ 6 }) in 1962 by an English chemist, a large no. of xenon compounds have been found and studied. So far, more than 100 compounds of xenon have been synthesized. Although, most of them contain fluorine and oxygen. Given the closed-shell configuration of xenon, oxygen and fluorine have the required electronegativity to attract the loosely bounded lone pair of electrons present in its valance shell. Xenon has the most extensive chemistry in group 18. In most of the compounds, the oxidation state of xenon is similar to its neighbouring element Iodine in the immediately lower oxidation state.

#### Halides of Xenon

There are three known fluorides of Xenon. These fluoride formations are the starting step for any xenon compound to be formed.

##### 1. Xenon difluoride

It is prepared in the laboratory by heating xenon and fluorine in the molar ratio 1:3 in a nickel vessel at 400°C. { XeF }_{ 2 } is isolated by vacuum sublimation.

Catalyst Used: Nickle

Temperature: 637 K

Pressure: 1bar

Reaction:

Xe + { F }_{ 2 }{ XeF }_{ 2 }

It can also be obtained by reacting together Xe and { O }_{ 2 }{ F }_{ 2 } (oxygen difluoride).

Temperature: -118°C

Reaction:

Xe + { O }_{ 2 }{ F }_{ 2 }{ XeF }_{ 2 }+ { F }_{ 2 }

Properties:

It is a colourless solid crystal and sublime at room temperature. It can go under hydrolysis when treated with water. It is also soluble in HF and has a melting point of 303 K.

Crystals of XeF2

##### 2. Xenon tetrafluoride

XeF4 is prepared in the laboratory by heating a mixture of xenon and fluorine in the molar ratio 1:5 in an enclosed nickel vessel.

Catalyst Used: Nickle

Temperature: 873 K

Pressure: 7 bar

Reaction:

Xe + 2{ F }_{ 2 }{ XeF }_{ 4 }

Properties:

It is a colourless crystalline solid and can sublimate. It melts at 390 K. { XeF }_{ 4 } is a strongly oxidising and fluorinating agent.

##### 3. Xenon hexafluoride

{ XeF }_{ 4 } can be prepared in the laboratory by heating a mixture of xenon and fluorine in the ratio 1:20, in a nickel vessel under pressure.

Catalyst Used: Nickle

Temperature: 600 K

Pressure: 60-70 bar

Reaction:

Xe + 3{ F }_{ 2 }{ XeF }_{ 6 }

It can also be obtained by reacting { XeF }_{ 4 } with { O }_{ 2 }{ F }_{ 2 }.

Temperature: 600 K.

Reaction:

{ XeF }_{ 4 } + { O }_{ 2 }{ F }_{ 2 }{ XeF }_{ 6 } + { O }_{ 2 }

Properties:

It is a strong fluorinating and oxidising agent. With HF, it gives an ionic compound [{ XeF }_{ 5 }]^{ + }+[{ HF }_{ 2 }]^{ - }.

HF + { XeF }_{ 4 }{ XeF }_{ 5 }^{ + }{ HF }_{ 2 }^{ - }[{ XeF }_{ 5 }]^{ + }+[{ HF }_{ 2 }]^{ - }.

#### Oxides of xenon

##### 1. Xenon trioxide

Xenon trioxide is an unstable compound of xenon and has a +6 oxidation state. Xenon trioxide ({ XeO }_{ 3 }) may be prepared by the hydrolysis of { XeF }_{ 4 } or { XeF }_{ 4 }.

{ XeF }_{ 6 } + 3{ H }_{ 2 }{ O }{ XeO }_{ 3 } + 6HF

6{ XeF }_{ 4 } + 12{ H }_{ 2 }{ O }2{ XeO }_{ 3 } + 4{ Xe } + 3{ O }_{ 2 } + 24HF

Properties:

{ XeO }_{ 3 } is a white, non–volatile, dissolvable solid. It is soluble in water. When dry, it explodes on heating or by any mechanical shock.

Its aqueous solution is weakly acidic due to the formation of xenic acid ({H}_{2}{ XeO }_{ 4 }).

{ XeO }_{ 3 } + 3{ H }_{ 2 }{ O }{H}_{2}{ XeO }_{ 4 } ⇔  { H }_{ }^{ + }{ XeO }_{ 4 }^{ - } .

##### 2. Xenon tetraoxide

Xenon tetraoxide is a relatively stable oxy-compound of xenon. All eight valence electrons of xenon are involved in making bonds with oxygen, and the oxidation state of the xenon atom is +8.

It is prepared by treating Barium Perxenate ({ Ba }_{ 2 }{ XeO }_{ 6 }) with anhydrous sulphuric acid.

{ Ba }_{ 2 }{ XeO }_{ 6 } + 2{ H }_{ 2 }{ SO }_{ 4 }2{ Ba }{ SO }_{ 4 } + { H }_{ 4 }{ XeO }_{ 6 }

Perxenic acid ({ H }_{ 4 }{ XeO }_{ 6 }) is then dehydrated to give xenon tetroxide.

{ H }_{ 4 }{ XeO }_{ 6 }2{ H }_{ 2 }{ O } + { XeO }_{ 4 }

Properties:

It is a yellow crystalline solid which is stable below -35 °C but very prone to exploding and decomposing into elemental Xenon and Oxygen above this temperature. Xenon tetroxide dissolves in water to form perxenic acid and in alkalis to form perxenate salts.

{ XeO }_{ 4 } + 2{ H }_{ 2 }{ O }{ H }_{ 4 }{ XeO }_{ 6 }

{ XeO }_{ 4 } + 4{ Na }{ OH }{ Na }_{ 4 }{ XeO }_{ 6 } + 2{ H }_{ 2 }{ O }

##### 3. Oxohalides of Xenon

The oxyfluorides of Xenon are mostly prepared by treating Xenon with Oxygen difluorides, and by the partial hydrolysis of Xenon halides.

{ XeF }_{ 4 } + { H }_{ 2 }{ O }{ XeOF }_{ 2 } + 2HF

{ XeF }_{ 6 } + { H }_{ 2 }{ O }{ XeOF }_{ 4 } + 2HF

Xenon tetroxide can also react with xenon hexafluoride to give xenon oxyfluorides.

{ XeO }_{ 4 } + { XeF }_{ 6 }{ XeOF }_{ 4 } + { XeO }_{ 3 }{ F }_{ 2 }

{ XeO }_{ 4 } + 2{ XeF }_{ 6 }2{ XeOF }_{ 4 } + { XeO }_{ 2 }{ F }_{ 4 }

Other Compounds

Xenon can also form compounds with other elements that have less electronegativity than oxygen and fluorine. In particular, carbon, along with other electron-withdrawing elements such as fluorine, can form a group that can stabilize such compounds. Some examples of such compounds are:

• [{ C }_{ 6 }{ F }_{ 5 }]_{ 2 }{ Xe }
• { C }_{ 6 }{ F }_{ 5 }–{ Xe }–{ F }

## Uses of Xenon

Although xenon is rare in the earth’s atmosphere, and therefore, it is relatively expensive than other gases, it has found itself quite an employability in society. It has various applications ranging from headlamps to the medical equipment.

### 1. Lights And Optics

Xenon is used to manufacture camera flashes and other strobe lights for photography and club-lights.

Xenon is used in lasers to increase the optical gain by exciting the active medium which, in turn, produces coherent light. The first solid-state laser was pumped with a xenon flash-lamp.

Xenon Based Ruby laser pumping device

Solar simulators use high-pressure short-arc Xenon lamps to produce artificial noon sunlight.

Xenon is also used in film projection technologies such as IMAX. Projectors use xenon bulbs that can consume up to 15000 Watts to light up the big IMAX screens.

Xenon Lamps emit very excellent short-wavelength UV-rays and intense near-infrared lights that are used to make night vision technologies. Xenon is used in plasma TV. Each cell in a plasma display is made up of a mixture of xenon and neon. Each interaction of this plasma with the electrodes generates ultraviolet photons, which then excite the phosphor coating on the front of the displays.

### 2. Medical Uses

Xenon is generally used as an anaesthetic, though it is not a cheaper alternative. It is also used as neuro and cardioprotective.

Health care professionals treating a patient with Xenon Anaesthetics before surgery

Inhaling a mixture of xenon and oxygen can increase athletic productivity in a human being by increasing the red blood cell production in the body. However, it is a prohibited substance and falls under the category of sports doping.

Radioisotope _{ }^{ 133 }{ X }e is used to make single-photon emission computed tomography machines, whereas _{ }^{ 129 }{ X }e is used as a contrast agent in MRI scanning.

Computed Blood flow Mapping with Xenon based CT scan.

Xenon Chloride is used to make excimer lasers that are used by dermatologists to perform surgery. Xenon has a large atomic structure, and therefore, it’s spin no. has a low sensitivity to magnetic effects. By making use of this property, we can use NMR spectroscopy to study the behaviour of the solvents in which Xenon is dissolved.

### Miscellaneous  Uses

Whenever there is a need for a heavy and chemically inert element for probes and bubble chambers, xenon is the most desirable choice for high-energy research. It is also used in gamma-ray calorimeters and as a detector of hypothetical Weakly Interacting Massive Particles.

A xenon ion collision recorded by the LHCb detector

Xenon has a low ionisation potential per atomic weight and can be stored as a liquid at room temperature. It is therefore preferred as a propellant for ion propulsion of space-crafts.

Chemically, perxenates are used as an oxidizing agent, and xenon is also used in protein crystallography. Xenon difluoride is also used in the production of an anticancerous drug, 5- Fluorouracil.

## Health Aspects

Under normal circumstances, xenon is chemically inert, non-toxic, and safe unless inhaled in high concentrations. Xenon gas is usually stored in metal or sealed glass containers. Keeping xenon in rubber or plastic containers is unsafe. Exposure through inhalation may cause side effects, such as loss of consciousness, vomiting, nausea, dizziness, deep coma, and even death. The symptoms include fatigue, emotional instability, air hunger, convulsions, and nausea.

Some of its radioactive isotopes can have harmful effects on pregnant women and may cause infertility if exposed.