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Argon (18 Ar) has 26 known isotopes, from 29 Ar to 54 Ar, of which three are stable (36 Ar, 38 Ar, and 40 Ar). On the Earth, 40 Ar makes up 99.6% of natural argon. The longest-lived radioactive isotopes are 39 Ar with a half-life of 268 years, 42 Ar with a half-life of 32.9 years, and 37 Ar with a half-life of 35.04 days.
However there are numerous exceptions; for example the lightest exception is chromium, which would be predicted to have the configuration 1s 2 2s 2 2p 6 3s 2 3p 6 3d 4 4s 2, written as [Ar] 3d 4 4s 2, but whose actual configuration given in the table below is [Ar] 3d 5 4s 1.
Argon (symbol Ar) is the third element in group 18, the noble gases. Argon is the third most common gas in the Earth's atmosphere , at 0.93%, making it more common than carbon dioxide . Nearly all of this argon is radiogenic argon-40 derived from the decay of potassium-40 in the Earth's crust.
Ne, 10, neon : 1s 2 2s 2 2p 6 Ar, 18, argon : 1s 2 2s 2 2p 6 3s 2 3p 6 Kr, 36, krypton : 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 Xe, 54, xenon : 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 Rn, 86, radon : 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 10 6p 6 Og, 118, oganesson : 1s 2 2s 2 2p 6 3s 2 3p 6 4s ...
Ar is the reason the standard atomic weight of terrestrial argon is greater than that of the next element, potassium, a fact that was puzzling when argon was discovered. Mendeleev positioned the elements on his periodic table in order of atomic weight, but the inertness of argon suggested a placement before the reactive alkali metal .
Neon has three main stable isotopes: 20 Ne, 21 Ne and 22 Ne, with 20 Ne produced by cosmic nucleogenic reactions, causing high abundance in the atmosphere. [ 97 ] [ 103 ] 21 Ne and 22 Ne are produced in the earth's crust as a result of interactions between alpha and neutron particles with light elements; 18 O, 19 F and 24,25 Mg. [ 104 ]
Ar argon: 18 3s 2 3p 6: 1s² 2s² 2p⁶ 3s² 3p⁶, [Ne] 3s² 3p⁶ : 1 S 0: S: 19 K potassium: 1 4s 1 [Ar] 4s¹, 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ : 2 S 1/2: S: 20 Ca calcium: 2 4s 2 [Ar] 4s², 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² : 1 S 0: S: 21 Sc scandium: 3 3d 1 4s 2 [Ar] 3d¹ 4s², 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹ 4s² : 2 D 3/2: D: 22 Ti titanium ...
Solid argon-hydrogen clathrate (Ar(H 2) 2) has the same crystal structure as the MgZn 2 Laves phase. It forms at pressures between 4.3 and 220 GPa, though Raman measurements suggest that the H 2 molecules in Ar(H 2) 2 dissociate above 175 GPa. A similar Kr(H 2) 4 solid forms at pressures above 5 GPa. It has a face-centered cubic structure where ...