18 - Argon noble gas
Discovered by Lord Rayleigh in 1894
- Atomic Radius (Å)
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).
| Shell | Electrons | Orbitals |
|---|---|---|
| 1 | 2 | 2 in 1s |
| 2 | 8 | 2 in 2s + 6 in 2p |
| 3 | 8 | 2 in 3s + 6 in 3p |
39.95 u
Atomic Mass
0.88 Å
Atomic Radius
87.3 K
Boiling Point
1.06 Å
Covalent Radius
1.78e-3 g/cm³
Density
-9.60e+1
Electron Affinity
15.76 eV
First Ionization Energy
83.96 K
Melting Point
3
Number of Shells
8
Electron Valency
18
Atomic Number
2, 8, 8
Electron Shell Occupations
