Argon
Element 18 on the periodic table, symbol Ar, group 18, period 3.
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).
Appearance: colorless gas exhibiting a lilac/violet glow when placed in a high voltage electric field
Properties
- Atomic Number
- 18
- Atomic Mass
- 39.9481 u
- Group
- 18
- Period
- 3
- Block
- p-block
- Category
- Noble Gas
- State at 25 °C
- Gas
- Melting Point
- 83.8 K · -189.3 °C
- Boiling Point
- 87.3 K · -185.8 °C
- Density
- 1.784 g/L
- Atomic Radius
- 71 pm
- Electronegativity
- Not measured
- Oxidation States
- None commonly seen
- Abundance in Crust
- 3.5 mg/kg
- Discovered
- 1894
- Discovered By
- Lord Rayleigh
Electron Configuration
[Ne] 3s2 3p6
1s2 2s2 2p6 3s2 3p6
Ionisation Energies (kJ/mol)
- 1. 1,520.6
- 2. 2,665.8
- 3. 3,931
- 4. 5,771
- 5. 7,238
- 6. 8,781
- 7. 11,995
- 8. 13,842
Elements near Argon
Elements in the same group share the number of outer electrons and behave in similar ways. Elements in the same period share a shell, so they change steadily from left to right.