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Argon is a chemical element; it has symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas . [ 10 ] Argon is the third most abundant gas in Earth's atmosphere , at 0.934% (9340 ppmv ).
The periodic table, also known as the periodic table of the elements, is an ordered arrangement of the chemical elements into rows ("periods") ... Argon 18 Ar 39.95 ...
The definitive visualisation of all 118 elements is the periodic table of the elements, ... Ar Argon: Greek argós 'idle' (it is inert) 18 3 p-block 39.95: 0.001 784:
Production of these two isotopes (36 Ar and 38 Ar) is negligible within the earth's crust, only limited concentrations of 38 Ar can be produced by interaction between alpha particles from decay of 235,238 U and 232 Th and light elements (37 Cl and 41 K). While 36 Ar is continuously being produced by Beta-decay of 36 Cl.
Ar 2 6 [Ar] 4s: 3d: 4p: 19 K 1-- 20 Ca ... The construction of the periodic table ignores these irregularities and is based on ideal electron configurations. [2]
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.
This is a list of chemical elements and their atomic properties, ordered by atomic number (Z).. Since valence electrons are not clearly defined for the d-block and f-block elements, there not being a clear point at which further ionisation becomes unprofitable, a purely formal definition as number of electrons in the outermost shell has been used.
The first table is for even-atomic numbered elements, which tend to have far more primordial nuclides, due to the stability conferred by proton-proton pairing. A second separate table is given for odd-atomic numbered elements, which tend to have far fewer stable and long-lived (primordial) unstable nuclides. [citation needed]