Symbol	Ar
Atomic number	18
Group	18 (Noble gases)
Period	3
Block	p
Classification	Noble Gas

Appearance	Colorless gas exhibiting a lilac/violet glow when placed in a high voltage electric field
Color	Colorless

Number of protons	18 p+
Number of neutrons	22 n0
Number of electrons	18 e-

From Wikipedia, the free encyclopediaArgon 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).

Phase at STP	Gas
Density	1.784 g/cm3
Atomic weight	39.792 u

Melting point	83.81 K -189.34 °C -308.812 °F
Boiling point	87.302 K -185.848 °C -302.5264 °F
Heat of vaporization	6.506 kJ/mol

Electronegativity (Pauling Scale)	-
Electron affinity	-96 kJ/mol
Oxidation states	0
Ionization energies	1520.6 kJ/mol 2665.8 kJ/mol 3931 kJ/mol 5771 kJ/mol 7238 kJ/mol 8781 kJ/mol 11995 kJ/mol 13842 kJ/mol 40760 kJ/mol 46186 kJ/mol 52002 kJ/mol 59653 kJ/mol 66199 kJ/mol 72918 kJ/mol 82473 kJ/mol 88576 kJ/mol 397605 kJ/mol 427066 kJ/mol

Electron configuration Shorthand configuration	[Ne] 3s2 3p6
Electron configuration Full configuration	1s2 2s2 2p6 3s2 3p6
Electron configuration chart	1s2 2s2 2p6 3s2 3p6
Electrons per shell	2, 8, 8
Valence electrons	8
Valency electrons	0
Bohr model	Figure: Shell diagram of Argon (Ar) atom.
Orbital Diagram	1s 2s 2p 3s 3p

Discovery and first isolation

Lord Rayleigh, William Ramsay (1894)

Discovery of argon Argon (Greek ἀργόν, neuter singular form of ἀργός meaning "lazy" or "inactive") is named in reference to its chemical inactivity. This chemical property of this first noble gas to be discovered impressed the namers. An unreactive gas was suspected to be a component of air by Henry Cavendish in 1785. Argon was first isolated from air in 1894 by Lord Rayleigh and Sir William Ramsay at University College London by removing oxygen, carbon dioxide, water, and nitrogen from a sample of clean air. They first accomplished this by replicating an experiment of Henry Cavendish's.

CAS Number	7440-37-1
ChemSpider ID	22407
EC number	231-147-0
PubChem CID Number	23968