Argon

Argon
Ar
In situ availability:
Necessity:
Atomic number:	18
Atomic mass:	39.948
group:	18
period:	3
normal phase:	Gas
series:	Noble gases
density:	1.784 g/L
melting point:	83.80K, -189.35°C, -308.83°F
boiling point:	87.30K, -185.85°C, -302.53°F
F ← Ne → N/A
Cl ← Ar → K
Br ← Kr → N/A
Atomic radius (pm):	71
Bohr radius (pm):	71
Covalent radius (pm):	97
Van der Waals radius (pm):	188
ionic radius (pm):	-
1st ion potential (eV):	15.76
Electron Configuration
1s2 2s2 2p6 3s2 3p6
Electrons Per Shell
2, 8, 8
Electronegativity:
Electron Affinity:	Unstable anion
Oxidation states:	-
Magnetism:	Nonmagnetic
Crystal structure:	Face centered cubic

Argon is a Noble gas in group 18. It has a Face centered cubic crystalline structure. This element has 3 stable isotopes: 36, 38, and 40.

Most of the volatiles have been deposited in the top layers of the Moon's surface by the solar wind over geologic time. A notable exception to this is Argon. The concentration of Argon in lunar soil is much higher than found in the solar wind, so must come from a different source. Especially, the isotope Argon-40. It is presently believed that the Argon-40 comes from radioactive decay of Potassium and/or Krypton deep within the lunar mantle or core, and that the Argon-40 seeps out to the surface via fissures. This lunar outgassing conitnues today. This vented Argon enter the lunar atmosphere; then the Argon is implanted into the regolith by interactions with ions from the solar wind.

Public domain info obtained from NASA:

Moon Fact Sheet

http://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html

Lunar Atmosphere Estimated Composition (particles per cubic cm):

Helium 4 (4He) - 40,000 Neon 20 (20Ne) - 40,000 Hydrogen (H2) - 35,000 Argon 40 (40Ar) - 30,000 Neon 22 (22Ne) - 5,000 Argon 36 (36Ar) - 2,000

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