What is Xenon?
Xenon is the chemical element, with the symbol Xe, which is an extreme and rare heavy gas of Group 18 (noble gases) of the periodic table. This was the first noble gas, which is found to form true chemical compounds. It is more than 4.5 times heavier than air, odourless, tasteless, and colourless. Solid xenon belongs to the cubic crystal system of face-centred, which implies that its molecules, consisting of single atoms, behave as spheres, which are packed together possibly closely. The term xenon is derived from the Greek word Xenos, which means “foreign” or “strange.”
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Properties of Xenon
Xenon occurs in very few traces as gases within the Earth and exists to the extent of up to 0.0000086 percent, or up to 1 part in 10 million by volume of dry air. Same as several other noble gases, xenon is also present in meteorites. Xenon can be manufactured on a small scale based on the fractional distillation of liquid air. It is the least volatile (with a boiling point, −108.0 °C) if the noble gases are obtainable from the air.
The element xenon can be used in lamps which produce extremely intense and short flashes of light, like stroboscopes and lights for high-speed photography. When an electrical charge is passed through the gas at low pressure, it emits a bluish-white light flash; at higher pressures, white light resembling daylight is emitted. Flash lamps of xenon can be used to activate ruby lasers.
Compounds
After the discovery that xenon can form chemical compounds by Neil Bartlett in 1962, a huge count of xenon compounds has been discovered and also described. Mostly all the known xenon compounds have the electronegative atoms oxygen or fluorine. The chemistry of xenon in every oxidation state is analogous compared to the neighbouring element iodine in the immediately lower oxidation state.
Halides
Three known fluorides, which are given as XeF2, XeF4, XeF6. XeF is the one, which is theorized to be unstable. These are the starting points for almost all xenon compound synthesis.
The crystalline and solid difluoride (XeF2) is produced when a mixture of xenon and fluorine gases is exposed to ultraviolet light. The ultraviolet component of the ordinary daylight is adequate—Heating XeF2 in long-term at higher temperatures under a NiF2 catalyst yields XeF6. XeF6 pyrolysis in the presence of NaF yields XeF4 with high-purity.
Oxides and Oxohalides
Three oxides of xenon are known: xenon tetroxide (XeO4) and xenon trioxide (XeO3), (both dangerously powerful and explosive oxidizing agents) and xenon dioxide (XeO2), reported in 2011 with a coordination number of four. XeO2 produces when the xenon tetrafluoride is poured over ice. Also, its crystal structure can allow it to replace the silicon in silicate minerals. The cation, XeOO+ has been identified by infrared spectroscopy in the solid argon.
Xenon does not directly react with oxygen, and the trioxide is produced by the hydrolysis of XeF6:
XeF6 + 3 H2O → XeO3 + 6HF
XeO3 is given as weakly acidic, dissolving in the alkali metal to form unstable xenate salts that contain the HXeO−4 anion. These unstable salts disproportionate to xenon gas and perxenate salts easily, which contain XeO4−6 anion.
Clathrates and Excimers
In addition to the compounds, in which xenon produces a chemical bond, xenon can produce the clathrates substances, in which xenon pairs or atoms are trapped by the crystalline lattice of the other compound. An example is given as xenon hydrate (Xe·5 3⁄4H2O), where xenon atoms occupy vacancies in a lattice of water molecules. This clathrate contains a melting point of 24 °C.
This hydrate’s deuterated version has also been produced. Another example is xenon hydride (Xe(H2)8), where xenon pairs (which are dimers) are trapped inside the solid hydrogen. Such clathrate hydrates may occur naturally under the conditions of high pressure, like in Lake Vostok underneath the Antarctic ice sheet. The clathrate formation is used to distil krypton, xenon, and argon fractionally.
Applications
Let us look at the use of xenon in various applications.
Illumination and Optics
Gas-discharge lamps: Xenon can be used in light-emitting devices, which are called xenon flash lamps, that can be used in stroboscopic lamps and photographic flashes; to excite the active medium in lasers and then generate coherent light, and in bactericidal lamps, occasionally. The first solid-state laser, which was invented in 1960, pumped by lasers and a xenon flash lamp, used to power inertial confinement fusion are also pumped by the xenon flash lamps.
Lasers
A group of researchers at Bell Laboratories discovered laser action in xenon in 1962, and later it was found that the laser gain was improved by adding the helium to the medium of lasing. The first excimer laser, which is a xenon dimer (Xe2) energized by an electrons beam to form stimulated emission at an ultraviolet wavelength of 176 nm. Xenon fluoride and xenon chloride have also been used in the excimer (or, exciplex, more accurately) lasers.
FAQs on Xenon
1. What is Xenon and where is it found in nature?
Xenon (symbol Xe) is a chemical element with atomic number 54. It is a dense, colourless, and odourless noble gas belonging to Group 18 of the periodic table. Xenon is extremely rare, occurring in trace amounts within the Earth's atmosphere at a concentration of about 1 part in 10 million by volume. It is commercially obtained as a byproduct from the fractional distillation of liquid air.
2. Why is Xenon often called the 'stranger gas'?
Xenon gets its name from the Greek word 'xenos', which translates to 'foreign' or 'strange'. It was named this by its discoverers in 1898 because it was an unexpected and 'foreign' element they identified after all the other known noble gases of the time (like argon and neon) had already been isolated from liquid air.
3. What key chemical properties allow Xenon to form compounds, unlike lighter noble gases?
Although Xenon is a noble gas with a stable, filled valence shell, it can form chemical compounds due to two main factors:
- Large Atomic Size: As one of the heavier noble gases, Xenon has a large atomic radius. This means its outermost electrons are far from the nucleus and less tightly held by the nuclear charge.
- Low Ionisation Enthalpy: Compared to lighter noble gases, Xenon has a relatively low ionisation enthalpy. This makes it energetically possible for a highly electronegative atom, such as fluorine or oxygen, to attract Xenon's valence electrons and form a chemical bond.
4. What are the different types of Xenon compounds, with examples?
Xenon primarily forms compounds with the most electronegative elements, fluorine and oxygen. The main types include:
- Xenon Fluorides: These are the starting point for most other xenon compounds. Examples are Xenon difluoride (XeF₂), Xenon tetrafluoride (XeF₄), and Xenon hexafluoride (XeF₆).
- Xenon Oxides: These are typically formed by the hydrolysis of xenon fluorides. Examples are Xenon trioxide (XeO₃) and Xenon tetroxide (XeO₄).
- Xenon Oxyfluorides: These are compounds where xenon is bonded to both oxygen and fluorine, such as Xenon oxyfluoride (XeOF₄).
5. What are the most important real-world applications of Xenon?
Xenon's unique properties make it valuable in several specialised fields. Its major applications include:
- High-Intensity Lighting: It is used in lamps that produce intense, bright flashes of light, such as in photographic flashes, stroboscopes, and high-end cinema projectors.
- Lasers: Xenon flash lamps are used to pump energy into the active medium in solid-state lasers, like ruby lasers.
- Medical Anaesthesia: Xenon can be used as a general anaesthetic. It has benefits like rapid onset and recovery, but its high cost limits its widespread use.
- Satellite Propulsion: Xenon is used as a propellant in ion thrusters for spacecraft and satellites due to its high atomic weight and inert nature.
6. Why is Xenon considered a rare and expensive gas?
Xenon is expensive mainly because of its extreme scarcity and the energy-intensive process required to isolate it. It makes up only about 0.086 parts per million of the Earth's atmosphere. The only commercially viable extraction method is the fractional distillation of massive quantities of liquefied air, which is a costly and complex industrial process to yield a very small amount of pure Xenon.
7. How can the structures of Xenon fluorides like XeF₂, XeF₄, and XeF₆ be explained?
The structures of Xenon fluorides are predicted using the VSEPR (Valence Shell Electron Pair Repulsion) theory, which considers the repulsion between bond pairs and lone pairs of electrons around the central Xenon atom:
- XeF₂: Has 2 bond pairs and 3 lone pairs, resulting in a linear structure to minimise repulsion.
- XeF₄: Has 4 bond pairs and 2 lone pairs, resulting in a square planar structure.
- XeF₆: Has 6 bond pairs and 1 lone pair, leading to a distorted octahedral structure.
8. What makes Xenon compounds like Xenon trioxide (XeO₃) particularly hazardous?
Xenon trioxide (XeO₃) is extremely hazardous because it is a highly unstable and powerful explosive. It is a solid compound that can detonate with great force upon heating or physical shock. This explosive nature is due to the weakness of the Xe-O bonds compared to the very strong O=O double bond in oxygen gas (O₂), making its decomposition into elemental Xenon and Oxygen a highly exothermic and rapid reaction.
