Argon (symbol Ar, atomic number 18) is the most common noble gas on Earth, used as an inert shielding atmosphere in welding. It is classified as a noble gas and sits in group 18, period 3 of the periodic table.
Overview
Argon is the chemical element with atomic number 18 and the symbol Ar. With a standard atomic weight of 39.95, it is a noble gas. In the periodic table it occupies group 18 and period 3, and under standard conditions it is normally a gas. Argon is the most common noble gas on Earth, used as an inert shielding atmosphere in welding.
Atomic structure
An atom of Argon has 18 protons in its nucleus and, when neutral, 18 electrons arranged in the configuration [Ne] 3s2 3p6. Its standard atomic weight of 39.95 reflects the natural mix of its stable isotopes.
Discovery and place in the table
Argon was discovered in 1894 by Lord Rayleigh, William Ramsay. It follows Chlorine (Cl) and precedes Potassium (K) in order of atomic number.
| Atomic number | 18 |
|---|---|
| Symbol | Ar |
| Atomic mass | 39.95 |
| Category | Noble gas |
| Group | 18 |
| Period | 3 |
| Electron configuration | [Ne] 3s2 3p6 |
| Phase at STP | Gas |
| Discovered | 1894 (Lord Rayleigh, William Ramsay) |