Krypton (Kr)
“The gas that hid in plain air until 1898 — and whose light once defined the very length of the metre.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
Characteristics
- Electron configuration [Ar] 3d¹⁰ 4s² 4p⁶ — a complete octet, so it neither gives, takes nor shares electrons and drifts along as a single unreactive atom (Period 4, Group 18).
- Roughly three times denser than air — one of the heaviest gases you will ever meet in everyday chemistry.
- Not perfectly inert after all: in 1963 chemists forced it into krypton difluoride (KrF₂), possible only with the fiercest oxidiser of all, fluorine.
- Under intense electric pulses it throws out brilliant white flashes — brighter than sunlight for a split second — the classic lamp of high-speed photography.
- Separated from liquid air by fractional distillation; squeezing out one litre of krypton means processing roughly a million litres of air.
A colourless, odourless, tasteless gas at room temperature, present in air at only about one part per million. Like its noble-gas cousins it drifts about as single atoms, and in a discharge tube it glows a pale bluish-white.
Where you meet it
✦ Uses
- Krypton-filled incandescent bulbs and the sealed lamps lighting airport runways — the heavy gas slows the filament’s evaporation, so lamps run hotter, brighter and longer.
- Krypton flash lamps of high-speed photography, which once froze bullets and bursting balloons in mid-flight in famous lab images.
- Krypton-fluoride excimer lasers (248-nanometre UV) that reshape the cornea in LASIK eye surgery and etch microchip patterns.
- From 1960 to 1983 the metre itself was defined as 1,650,763.73 wavelengths of the orange-red light of krypton-86 — every ruler traced back to this gas.
◍ Everyday examples
- Every breath you take carries krypton atoms — about a millionth of the air — and they leave your body completely unchanged.
- The strings of runway and approach lights guiding night flights into Dhaka’s airport are the high-performance gas-filled lamps of the family krypton powers.
- Superman’s fictional weakness “kryptonite” borrowed this element’s name — the two share nothing but the fame.
History & name
On 30 May 1898 William Ramsay and Morris Travers in London were left with a few drops of residue after distilling argon out of liquid air. They ran a current through it, the tube lit up, and the spectroscope showed unfamiliar lines — another new element was hiding in ordinary air. Within two months the same residue would also surrender neon and xenon. Because the gas had stayed concealed so long, they named it krypton from the Greek kryptos, “the hidden one”.