Atomic Properties of Ar
- Atomic Number of Ar
- 18
- Atomic Mass of Ar
- 39.9480 u
- Electron Configuration
- [Ne] 3s2 3p6
- Electronegativity
- —
- Block
- p-block
- Group
- 18
- Period
- 3
Argon hid inside a measurement discrepancy. Lord Rayleigh found that nitrogen isolated from air was slightly denser than nitrogen made from chemical compounds. William Ramsay helped remove the reactive gases, leaving an unfamiliar residue. In 1894 they identified argon, named from argos, Greek for inactive. Careful weighing had uncovered 0.93 percent of the atmosphere.
Its abundance has a nuclear origin. Potassium-40 inside rocks can decay by electron capture to argon-40. Over geological time, that argon escapes into the atmosphere, making argon-40 by far the dominant terrestrial isotope. In a cooled mineral, newly formed argon can become trapped. Measuring potassium and argon therefore provides a clock for volcanic rocks and ancient geological events.
Argon's filled valence shell makes it chemically inert under ordinary conditions. That passivity creates a protective atmosphere. Welders use flowing argon to keep hot metal away from oxygen and nitrogen. Crystal growers, semiconductor processes, and laboratories use it to exclude reactive air. Incandescent bulbs use argon to slow evaporation of a hot tungsten filament. The gas does not strengthen a weld or crystal directly; it protects the process from unwanted chemistry.
Industry obtains argon during fractional distillation of liquid air. It is colorless and odorless, and although nontoxic, it can displace oxygen without warning in confined spaces. Inert does not mean harmless in every setting.
Argon is Still enough to preserve a molten surface and patient enough to record geological time. Its discovery, uses, and isotope clock all depend on what it refuses to do: react readily, disappear from a sealed mineral, or reveal itself without precise measurement.