Xenon

Xenon (Xe) is a chemical element and a rare, heavy gas that is classified in Group 18 of the periodic table, which includes noble gases. It was the first noble gas identified to form genuine chemical compounds. With a density of more than 4.5 times that of air, Xenon is colourless, odourless, and tasteless. Its name comes from the Greek word "xenos," which means "strange" or "foreign."

1.0Introduction

Xenon, a noble gas discovered in 1898 by William Ramsay and Morris Travers, is generally inert but can form compounds like xenon hexafluoride (XeF6), xenon difluoride (XeF2), and xenon tetrafluoride (XeF4) under certain conditions, challenging the idea of noble gases being completely non-reactive. Its high density and low boiling point make it valuable for high-intensity lamps and medical imaging applications. In its solid form, Xenon has a face-centred cubic crystal structure with closely packed, monatomic atoms.

 Xenon is present in the Earth's atmosphere in trace amounts, making up about 0.0000086 percent or 1 part in 10 million dry air. It is also present in meteorites and can be produced on a small scale through the fractional distillation of liquid air. With a boiling point of −108.0 °C, Xenon is the least volatile among the noble gases obtained from air.

2.0Xenon Properties

Physical Properties:

• Atomic Number: 54
• Molar Mass: 131.293 g/mol
• Colour: Xenon emits a bright bluish-white light at temperatures between 4000 K and 6000 K.
• Odour: Xenon is odourless.
• Melting Point: 161.4 K
• Boiling Point: 165.051 K
• Density: 0.005366 g/cm³

Chemical Properties:

• Inert Gas: Xenon is generally non-reactive but can form compounds under specific conditions.
• Oxidation States: Xenon exhibits five oxidation states: +1, +2, +4, +6, +8.

3.0Compounds of Xenon

Following Neil Bartlett's groundbreaking 1962 discovery that xenon could form chemical compounds, a wide array of xenon compounds has been identified and studied. Most of these compounds include highly electronegative atoms such as oxygen or fluorine. The chemistry of xenon in its various oxidation states closely parallels that of iodine in corresponding lower oxidation states.

• Halides

Xenon fluorides are fascinating compounds due to their unique chemistry involving a noble gas. Here's a summary of the xenon fluorides mentioned:

1. Xenon Di-fluoride (XeF₂):

• Synthesis: Produced by exposing a mixture of xenon (Xe) and fluorine (F₂) gases to ultraviolet (UV) light. Daylight is sufficient for this reaction because it contains enough UV radiation to drive the formation of XeF₂.

$\text{ - Reaction: }\mathrm{Xe}+{\mathrm{F}}_2\stackrel{\mathrm{UV}}{\to }{\mathrm{XeF}}_2$

Xenon Tetrafluoride (XeF₄):

• Synthesis: Obtained by pyrolyzing xenon hexafluoride (XeF₆) in the presence of sodium fluoride (NaF). Pyrolysis involves heating the XeF₆ to decompose it into XeF₄ and other byproducts.

$\text{ - Reaction: }{\mathrm{XeF}}_6\stackrel{\text{ heat, }\mathrm{NaF}}{\to }{\mathrm{XeF}}_4+\text{ byp }$

2. Xenon Hexafluoride (XeF₆):

• Synthesis: Formed by heating xenon di-fluoride (XeF₂) over a nickel fluoride (NiF₂) catalyst at high temperatures. This process increases the fluorination state of xenon. 

$\text{ - Reaction: }{\mathrm{XeF}}_2\stackrel{\text{ heat, }{\mathrm{NiF}}_2}{\to }{\mathrm{XeF}}_6$

Stability of Xenon Fluorides:

XeF: Although theorised to exist, xenon mono-fluoride (XeF) is considered unstable and is not typically encountered in practical situations. Its instability is due to the high reactivity and the difficulty in stabilising a monovalent xenon species.

The transformations between these compounds reflect the underlying chemistry of xenon, a noble gas that can form multiple oxidation states and complex compounds with fluorine, a highly reactive element.

• Oxides and Oxohalides

Three oxides of Xenon are known: xenon tetroxide (XeO4), xenon trioxide (XeO3), and xenon dioxide (XeO2). Both XeO4 and XeO3 are dangerously powerful and explosive oxidizing agents. Xenon dioxide (XeO2), reported in 2011, has a coordination number of four and can be produced when xenon tetrafluoride (XeF4) is poured over ice. Its crystal structure allows it to substitute for silicon in silicate minerals potentially. The cation XeOO+ has also been identified by infrared spectroscopy in solid argon.

Xenon does not directly react with oxygen; instead, xenon trioxide (XeO₃) is produced through the hydrolysis of xenon hexafluoride (XeF₆) as shown in the reaction:

XeF₆+3H₂O→XeO₃+6HF

XeO₃ is weakly acidic and dissolves in alkali metals to form unstable xenate salts containing the HXeO₄⁻ anion. These unstable salts are readily disproportionate into xenon gas and perxenate salts, which contain the XeO₆⁴⁻ anion.

4.0Application of xenon 

Xenon’s inertness, high density, and bright light emission make it valuable in these diverse applications. Xenon is a versatile element with applications across various fields:

1. Lighting: Used in xenon arc lamps, HID car headlights, and flash tubes for photography due to its bright white light.
2. Medical Applications: Employed as a general anaesthetic and in medical imaging (CT and MRI) with xenon-133.
3. Space Exploration: Serves as a propellant in ion thrusters for spacecraft, ideal for long missions.
4. Scientific Research: Utilized in NMR, MRI, and particle detectors, particularly in dark matter research.
5. Industrial Uses: Applied in semiconductor manufacturing, plasma etching, and excimer lasers for microchip production.

Environmental Science: Used in trace gas analysis to study atmospheric changes.