# Argon

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 *A*r, std(Ar) | [7001397920000000000♠39.792, 7001399630000000000♠39.963] conventional: 7001399480000000000♠39.948 |
| Argon in the periodic cairt |
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|  |  |  |
| --- | --- | --- |
| 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 (*t*1/2) | 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 |
|

**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.