Tukuk-OSArgon
Noble gas · atomic number 18
Argon is a chemical element with symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third most common gas in the Earth's atmosphere, at 0.934% (9,340 ppmv), making it over twice as abundant as the next most common atmospheric gas, water vapor (which averages about 4000 ppmv, but varies greatly), and 23 times as abundant as the next most common non-condensing atmospheric gas, carbon dioxide (400 ppmv), and more than 500 times as abundant as the next most common noble gas, neon (18 ppmv).
Properties of Argon
| Element category | Noble gas |
|---|---|
| Atomic number | 18 |
| Atomic mass | 39.9481 u |
| Phase at STP | Gas |
| Group | 18 |
| Period | 3 |
| Block | p |
| Electron configuration | [Ne] 3s2 3p6 |
| Electrons per shell | 2, 8, 8 |
| Melting point | 83.81 K (-189 °C) |
| Boiling point | 87.302 K (-186 °C) |
| Density | 1.784 g/L |
| Discovered by | Lord Rayleigh |
← Chlorine · Periodic table · Potassium → K
About the noble gas group
Full outer electron shells make these gases almost inert: they barely react, glow in discharge lamps and are used to create unreactive atmospheres.