Argon (Ar)
Noble gas · p-block · period 3 · group 18
Colourless, odourless, unreactive gas.
Argon (symbol Ar) is chemical element number 18, a noble gas in group 18, period 3 of the periodic table. Its standard atomic weight is 39.95 and its electron configuration is [Ne] 3s2 3p6. At room temperature it is a gas. Its name means 'the lazy one' in Greek, for its refusal to react.
Properties
| Atomic number | 18 |
|---|---|
| Atomic mass | 39.95 |
| Category | Noble gas |
| Block | p-block |
| Group · Period | 18 · 3 |
| Electron configuration | [Ne] 3s2 3p6 |
| Electrons per shell | 2, 8, 8 |
| State at 25 °C | gas |
| Melting point | 83.8 K |
| Boiling point | 87.3 K |
| Density | 1.784 g/L |
| Electronegativity (Pauling) | — |
| Radioactive | No |
| Origin | primordial |
| Discovered | 1894 · Rayleigh & Ramsay |
Key facts about Argon
- Its name means 'the lazy one' in Greek, for its refusal to react.
- The third most abundant gas in air, at about 0.93%.
- Fills incandescent light bulbs to stop the filament burning up.
- Welders blanket the weld pool with argon to keep oxygen away.
What Argon is used for
Welding shields, light bulbs, double-glazing gas fill, protective atmospheres, lasers.
Where it sits in the periodic table
Argon is in group 18, period 3, of the p-block. Its electron configuration [Ne] 3s2 3p6 means its outermost shell holds 8 electrons, which is what places it here and explains much of its chemistry. See Argon on the interactive table →
Argon — frequently asked questions
What is Argon used for?
Welding shields, light bulbs, double-glazing gas fill, protective atmospheres, lasers.
Is Argon radioactive?
No. Argon has at least one stable isotope and is not radioactive.
What is the electron configuration of Argon?
Argon has the electron configuration [Ne] 3s2 3p6, which is 2, 8, 8 electrons per shell.
What group and period is Argon in?
Argon is in group 18, period 3, in the p-block. Its outer shell holds 8 electrons.
Who discovered Argon?
Argon was discovered in 1894 by Rayleigh & Ramsay.