Argon vs Krypton
Both are noble gass, so they share the same broad chemistry.
The differences in plain English
- They sit in the same column, group 18, so they have the same number of outer electrons and react in similar ways; the heavier one, Krypton, is usually the more reactive of the two if they are metals, and the less reactive if they are non-metals.
- Both are gass at room temperature.
- Krypton is denser, about 2.1 times more than Argon (3.749 against 1.784 g/L).
- Krypton melts at -157 °C, Argon at -189 °C.
- An atom of Krypton is about 2.1 times heavier than an atom of Argon (83.80 u against 39.95 u).
Side by side
| Argon | Krypton | |
|---|---|---|
| Atomic number | 18 | 36 |
| Symbol | Ar | Kr |
| Family | Noble gas | Noble gas |
| Group / period | 18 / 3 | 18 / 4 |
| State at room temperature | Gas | Gas |
| Atomic mass | 39.948 u | 83.798 u |
| Density | 1.784 g/L | 3.749 g/L |
| Melting point | -189 °C | -157 °C |
| Boiling point | -186 °C | -153 °C |
| Electronegativity | – | 3 |
| First ionisation energy | 1520.6 kJ/mol | 1350.8 kJ/mol |
| Electron configuration | [Ne] 3s2 3p6 | [Ar] 3d10 4s2 4p6 |
| Discovered by | Lord Rayleigh | William Ramsay |
Argon
Take a deep breath. Around one per cent of what you just inhaled was argon, and every bit of it will come straight back out again unchanged. Argon does not burn, does not corrode anything and does not take part in chemistry of any kind. Its name comes from the Greek for idle or lazy, and it earned it.
- Argon was the first noble gas to be discovered, and its discovery earned Nobel Prizes in both physics and chemistry in the same year, 1904.
- Almost all of Earth's argon was made by the radioactive decay of potassium in rocks, and potassium-argon dating uses that build-up to work out the age of ancient lava flows.
Krypton
Every breath you take contains about one part per million of krypton. It is colourless, odourless and almost entirely unreactive, which is why it escaped notice until 1898 and why its discoverers named it from the Greek kryptos, meaning hidden. Forty years later a comic book borrowed the name for Superman's home planet, and the fictional planet has been better known than the real gas ever since.
- From 1960 to 1983 the metre was officially defined as a fixed number of wavelengths of orange-red light emitted by krypton-86 atoms.
- Krypton was discovered in May 1898, and the same two scientists found neon within weeks and xenon a few weeks after that.
Colour the bubbles by density or melting point and the difference jumps out.
More comparisons
Data from Periodic-Table-JSON (CC BY-SA); temperatures rounded to the nearest degree. Written by Anthony.