Argon

Argon is a chemical element wi seembol Ar an atomic nummer 18. It is in group 18 o the periodic table an is a noble gas. Argon is the third maist common gas in the Yird's atmosphere, at 0.93% (9,300 ppm), makin it approximately 23.8 times as abundant as the next maist common atmospheric gas, carbon dioxide (390 ppm), an mair nor 500 times as abundant as the next maist common noble gas, neon (18 ppm). Near aw o this argon is radiogenic argon-40 derived frae the decay o potassium-40 in the Yird's crust. In the universe, argon-36 is bi far the maist common argon isotope, bein the preferred argon isotope produced bi stellar nucleosynthesis in supernovas.

Argon, ₁₈Ar

Argon
Pronunciation	/ˈɑːrɡɒn/ ​(AR-gon)
Appearance	colourless gas exhibitin a laylock/violet glowe whan placed in a heich voltage electric field
Standard atomic weight Ar, std(Ar)	[7001397920000000000♠39.792, 7001399630000000000♠39.963] conventional: 7001399480000000000♠39.948
Argon in the periodic cairt
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Airn Cobalt Nickel Capper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Siller (element) Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gowd Mercur (element) Thallium Leid (element) Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Ununtrium Flerovium Ununpentium Livermorium Ununseptium Ununoctium Ne ↑ Ar ↓ Kr chlorine ← argon → potassium
Atomic nummer (Z)	18
Group	group 18 (noble gases)
Period	period 3
Block	p-block
Element category	Noble gas
Electron confeeguration	[Ne] 3s2 3p6
Electrons per shell	2, 8, 8
Pheesical properties
Phase at STP	gas
Meltin pynt	83.81 K ​(−189.34 °C, ​−308.81 °F)
Bylin pynt	87.302 K ​(−185.848 °C, ​−302.526 °F)
Density (at STP)	1.784 g/L
whan liquid (at b.p.)	1.40 g/cm3
Treeple pynt	83.8058 K, ​68.89 kPa
Creetical pynt	150.687 K, 4.863 MPa
Heat o fusion	1.18 kJ/mol
Heat o vapourisation	6.43 kJ/mol
Molar heat capacity	5R/2 = 20.786 (Cp) J/(mol·K)
Vapour pressur P (Pa) 1 10 100 1 k 10 k 100 k at T (K)   47 53 61 71 87
Atomic properties
Oxidation states	0
Electronegativity	Pauling scale: no data
Ionisation energies	(more)
Covalent radius	106±10 pm
Van der Waals radius	188 pm
Colour lines in a spectral range Spectral lines o argon
Ither properties
Naitural occurrence	primordial
Creestal structur	​face-centred cubic (fcc)
Speed o soond	(gas, 27 °C) 323 m/s
Thermal conductivity	17.72×10−3  W/(m·K)
Magnetic orderin	diamagnetic
CAS Nummer	7440–37–1
History
Diskivery	Lord Rayleigh an William Ramsay (1894)
First isolation	Lord Rayleigh an William Ramsay (1894)
Main isotopes o argon
Iso­tope Abun­dance Hauf-life (t1/2) Decay mode Pro­duct 36Ar 0.337% - (β+β+) 36S 37Ar syn 35 d ε 37Cl 38Ar 0.063% stable 39Ar trace 269 y β− 39K 40Ar 99.600% stable 41Ar syn 109.34 min β− 41K 42Ar syn 32.9 y β− 42K
Decay modes in parentheses is predict, but hisna yet been observed