Quick Facts
| Property | Value |
|---|---|
| Symbol | Kr |
| Atomic Number | 36 |
| Atomic Mass | 83.798 u |
| Category | Noble Gas |
| Period | 4 |
| Group | 18 |
| Block | p |
| Electron Configuration | [Ar] 3d¹⁰ 4s² 4p⁶ |
Physical Properties
| Property | Value |
|---|---|
| State at 20°C | Gas |
| Density | 0.003749 g/cm³ |
| Melting Point | -157.36°C (115.79 K) |
| Boiling Point | -153.22°C (119.93 K) |
| Appearance | Colorless gas (glows whitish in discharge) |
Atomic Properties
| Property | Value |
|---|---|
| Electron Configuration | [Ar] 3d¹⁰ 4s² 4p⁶ |
| Electronegativity | 3.00 (Pauling scale) |
| First Ionization Energy | 1350.8 kJ/mol |
| Atomic Radius | 88 pm |
| Covalent Radius | 116 pm |
| Van der Waals Radius | 202 pm |
History and Discovery
Discovered by: William Ramsay and Morris Travers Year of Discovery: 1898 Location: London, England
Etymology
The name "krypton" comes from the Greek "kryptos" meaning "hidden" or "secret," referring to its trace presence in the atmosphere.
Discovery Story
William Ramsay and Morris Travers discovered krypton in 1898 by evaporating liquid air and examining the fractions. They found a new gas with a characteristic spectrum between argon and a lighter component. The same team discovered neon and xenon the same year.
Isotopes
| Isotope | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|
| ⁷⁸Kr | 0.355% | Stable | - |
| ⁸⁰Kr | 2.286% | Stable | - |
| ⁸²Kr | 11.593% | Stable | - |
| ⁸³Kr | 11.500% | Stable | - |
| ⁸⁴Kr | 56.987% | Stable | - |
| ⁸⁶Kr | 17.279% | Stable | - |
Occurrence
Natural Abundance
Krypton is very rare, comprising only about 1 ppm of Earth's atmosphere. It is produced by cosmic ray interactions and radioactive decay. It does not accumulate in any concentrated form in nature.
Extraction and Production
- Fractional Distillation of Air: Only commercial source
- Byproduct: From liquid air separation for oxygen and nitrogen
- Production Volume: Small compared to other atmospheric gases
- About 8-10 tons produced annually
Applications and Uses
Lighting
- High-efficiency incandescent bulbs (krypton fill)
- Krypton-85 in fluorescent lamps
- Flash lamps for photography
- Airport runway lights
Lasers
- Krypton-fluoride excimer lasers
- Krypton-ion lasers (medical, scientific)
- Laser light shows
Scientific Applications
- Former definition of the meter (krypton-86 spectral line, 1960-1983)
- Insulating gas in windows
- Cryogenic research
Other Uses
- Nuclear medicine (krypton-81m for lung imaging)
- Leak detection in sealed containers
- Spacecraft ion propulsion (research)
Biological Role
Krypton has no known biological role. It is chemically inert and does not participate in biochemical processes.
In the Human Body
Krypton is not metabolized or used by the body. Trace amounts are inhaled and exhaled unchanged.
Medical Uses
Krypton-81m is used in nuclear medicine for lung ventilation studies.
Safety and Hazards
Toxicity
Krypton is non-toxic but can act as an asphyxiant by displacing oxygen in enclosed spaces.
Handling Precautions
- Can cause asphyxiation in confined spaces
- Compressed gas requires proper cylinder handling
- Liquid krypton causes frostbite
- No fire hazard—completely inert
Environmental Impact
Krypton is environmentally benign. Krypton-85 from nuclear reprocessing is a minor atmospheric contaminant but poses no significant risk.
Interesting Facts
- Krypton is not related to "kryptonite" from Superman comics—that was inspired by the Greek meaning "hidden"
- The meter was defined by a krypton-86 spectral line from 1960 to 1983
- Krypton is denser than air and can collect in low-lying areas
- Krypton can form compounds with fluorine (like krypton difluoride)
- Krypton lights are used at airports because they penetrate fog better