54XeXenon131.29

A real sample of the element Xenon — Real sample photo

Xenon (Xe)

“The stranger that broke chemistry’s strictest rule — aloof for sixty-four years, until 1962 when xenon stunned the world by forming real compounds.”

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Atomic number54

Atomic mass131.29

Group18

Period5

BlockP-block

PhaseGas

Electron structure

How its electrons are arranged

[Kr] 4d¹⁰ 5s² 5p⁶

Shell 1

2e⁻

Shell 2

8e⁻

Shell 3

18e⁻

Shell 4

18e⁻

Shell 5

8e⁻

Computed from the aufbau principle, with known real-world exceptions applied automatically.

🎯 Exam focus

Questions to practise

Try each question yourself first — then open it to read the full model answer.

1How did Ramsay and Travers coax xenon out of their liquid-air residue in July 1898, weeks after krypton had already been taken?

Model answerOn 12 July 1898, six weeks after bagging krypton, William Ramsay and Morris Travers fractionally distilled the very last drops of their liquid-air residue — the heavy fraction nobody had chased before. The trapped gas glowed a beautiful sky-blue, and the spectroscope showed a ladder of unknown lines: a new, heavier noble gas, which Ramsay named xenon, “the stranger”.

2Why do the blue-white headlamps of expensive cars carry the name “xenon lamps”, and what job does the gas do inside them?

Model answerBecause the light comes from xenon itself: inside an $\mathrm{HI}$ D headlamp a tiny arc of electricity leaps through xenon gas under high voltage, and the energised gas glows with a piercing blue-white, daylight-bright light that carries far down dark highways — no fragile filament involved. The gas is the arc’s medium and the lamp’s light-giver at once, so the lamps carry its name.

3Where might a Bangladeshi student meet xenon twice in the same year — once on the road and once in a hospital corridor?

Model answerOn the road, the piercing blue-white headlights of an expensive sedan at night are a small xenon arc at work. In the hospital, the same element may be working unseen — xenon is a genuine anaesthetic that puts surgical patients under safely, and xenon-chloride excimer lasers perform LASIK eye surgery — so the operating theatre and the eye clinic both host the stranger.

4Xenon has served as an anaesthetic even for heart-surgery patients — which of its properties makes it one of medicine’s safest sleeping gases, and why does rarity keep it rare in hospitals?

Model answerXenon dissolves into nerve tissue and switches consciousness off painlessly, then wears off remarkably fast — patients wake within about two minutes — with almost no side effects, which makes it safe even for heart-surgery patients. But xenon occurs in air only as a trace, extracted laboriously from liquid air, so supply is scarce and the price keeps hospital use rare.

5Starting from krypton’s closed shell, build xenon’s electron configuration and explain why sitting at the bottom of Group 18 makes this noble gas the family’s best chemist.

Model answerXenon builds directly on krypton’s closed shell: [Kr] 4d¹⁰ 5s² 5p⁶, the 5p subshell completing an octet of eight outer electrons. Its family talent comes from size: sitting at the bottom of Group 18, xenon holds its outermost electrons loosely, far from the nucleus, so a fiercely electronegative partner like fluorine can actually pull them away to make $\mathrm{XeF_{2}}$ , $\mathrm{XeF_{4}}$ and $\mathrm{XeF_{6}}$ — chemistry the small, tight-held atoms of helium and neon refuse.

6Helium and neon still refuse to form stable compounds, yet xenon reacts with fluorine — explain how xenon’s position in Group 18 makes it the “least noble” member of the family.

Model answerDescending Group 18 the atoms grow larger and their outer electrons sit farther from the nucleus, so the shielding octet becomes steadily easier to breach — the ionisation energy falls from helium’s fortress shell to xenon’s loose grip. Fluorine, the most electronegative element, can therefore wrest electrons from xenon to build $\mathrm{XeF_{2}}$ , $\mathrm{XeF_{4}}$ , $\mathrm{XeF_{6}}$ and even $\mathrm{XeO_{3}}$ , while helium and neon hold their electrons too firmly to react at all.

Study guides

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Quick answers

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Electron configurationThe full arrangement, step by step ValencyHow many bonds it forms Atomic massThe standard weight, explained Metal or nonmetalWhich family it belongs to Everyday usesWhere you meet it daily

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The notes

About the element

Characteristics

Electron configuration [Kr] 4d¹⁰ 5s² 5p⁶ — a filled outer shell of eight valence electrons (Period 5, Group 18), the textbook root of its aloofness.
Not truly inert after all: its huge atom holds its outer electrons loosely, so fierce fluorine can seize them — $\mathrm{XeF_{2}}$ , $\mathrm{XeF_{4}}$ , $\mathrm{XeF_{6}}$ and even $\mathrm{XeO_{3}}$ are known.
One of the heaviest gases you will ever meet — about 4.5 times the density of air; a balloon of it sinks, unlike helium or neon balloons.
A genuine anaesthetic: dissolved in nerve tissue, xenon switches consciousness off painlessly and wears off remarkably fast, with almost no side effects.

Appearance

A colourless, odourless, utterly quiet gas at room temperature — about four and a half times denser than air, the heaviest of the non-radioactive noble gases. Like the rest of its family it drifts around as single atoms, and in a sealed tube under high voltage it glows a striking blue-white.

Real world

Where you meet it

✦ Uses

Xenon ( $\mathrm{HI}$ D) car headlamps on premium cars — a tiny arc of xenon under high voltage throws crisp daylight-white beams far down dark highways.
Anaesthesia in the operating theatre — xenon puts patients under smoothly and lets them wake within about two minutes, safe enough even for heart-surgery patients.
Xenon-chloride excimer lasers whose ultraviolet pulses reshape the cornea in LASIK eye surgery; the same gas fills the flash lamps of cameras.
Ion thrusters on spacecraft and communications satellites — electric fields fling xenon ions backward at tens of kilometres per second, gently, for months on end.

◍ Everyday examples

On a Bangladeshi highway at night, the piercing blue-white headlights of an expensive sedan are a small xenon arc at work.
A friend or relative freed from spectacles by LASIK surgery owes that sharp vision partly to xenon’s invisible ultraviolet flashes.
NASA’s Dawn spacecraft toured the giant asteroid Vesta and the dwarf planet Ceres on nothing but the patient push of xenon ion engines.

Story

History & name

On 12 July 1898, six weeks after bagging krypton, William Ramsay and Morris Travers fractionally distilled the very last drops of their liquid-air residue — the heavy fraction nobody had bothered to chase. The tube glowed a beautiful sky-blue, and the spectroscope revealed a ladder of unknown lines: yet another new gas. Ramsay named it xenon from the Greek xenos, “stranger” — a guest that had lurked invisible in air since the planet formed. For sixty-four more years it kept its noble distance, until Neil Bartlett’s $\mathrm{XePtF_{6}}$ of 1962 shattered the textbook myth that noble gases never react.

Name originGreek xenos, “stranger” — a hidden guest in the liquid-air residue, unknown to chemists until 1898.

Neighbours

Nearby elements

The elements that sit right beside this one on the table — often the closest chemical cousins.

52TeTellurium127.60 53IIodine126.90 55CsCaesium132.91 56BaBarium137.33