Krypton (Kr)
Noble gas
Krypton is a rare noble gas best known for lending its name to Superman's home planet. In the real world it fills high-performance windows, camera flashes and some lasers — and from 1960 to 1983 the metre itself was defined by krypton light.
Position on the periodic table
Atomic properties
| Atomic number | 36 |
|---|---|
| Atomic mass | 83.7982 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 |
| Noble gas shorthand | [Ar] 3d10 4s2 4p6 |
| Electrons per shell | 2, 8, 18, 8 |
| Valence electrons (outer shell) | 8 |
| Common oxidation states | +2 |
| Electronegativity (Pauling) | 3 |
| Covalent radius (approx.) | 116 pm |
| First ionization energy | 1351 kJ/mol |
| Electron affinity | -96 kJ/mol |
Physical properties
| State at 25 °C | Gas |
|---|---|
| Density | 3.749 g/L |
| Melting point | -157.37 °C (115.78 K) |
| Boiling point | -153.22 °C (119.93 K) |
| Appearance | colorless gas, exhibiting a whitish glow in a high electric field |
| Radioactive | No |
| Origin | Occurs naturally |
Electron configuration of krypton
Krypton's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6, usually shortened to [Ar] 3d10 4s2 4p6. Its electrons occupy 4 shells (2, 8, 18, 8), placing it in period 4 of the p-block. The 8 outer-shell electrons drive its bonding behaviour. Explore it interactively in the electron configuration calculator.
Uses of krypton
- High-efficiency window insulation
- Photographic flashes and airport runway lights
- Krypton-fluoride excimer lasers
Biological role: None — inert.
Occurrence: About 1 part per million of the atmosphere, extracted from liquefied air.
Common compounds of krypton
KrF2
Krypton difluoride (unstable, lab-only)
History and discovery
Discovered: 1898 — William Ramsay. Name origin: From Greek kryptos, meaning hidden.
Discovered in 1898 by William Ramsay and Morris Travers in the residue of evaporated liquid air.
Safety notes
Non-toxic and inert; only a simple asphyxiant in confined spaces.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Krypton
1. What is the chemical symbol of Krypton?
2. What is the atomic number of Krypton?
3. Which category does Krypton belong to?
4. What is the state of Krypton at room temperature?
5. Which period of the periodic table is Krypton in?
Krypton FAQs
What is the atomic number of krypton?
Krypton's atomic number is 36 — every krypton atom has 36 protons in its nucleus.
What is the symbol for krypton?
Kr. From Greek kryptos, meaning hidden.
Is krypton a metal, nonmetal, or metalloid?
Krypton is classified as a noble gas.
What state is krypton at room temperature?
At about 25 °C, krypton is a gas. It melts at -157.37 °C.
How many valence electrons does krypton have?
Krypton has 8 electrons in its outer shell (shell pattern: 2, 8, 18, 8).
What is krypton used for?
Key uses include: high-efficiency window insulation; photographic flashes and airport runway lights; krypton-fluoride excimer lasers.
Related elements
Keep working with this element
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