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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 ).
Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic table: carbon is above it; and germanium, tin, lead, and flerovium are below it. It is relatively unreactive.
Silicon (14 Si) has 25 known isotopes, with mass numbers ranging from 22 to 46. 28 Si (the most abundant isotope, at 92.23%), 29 Si (4.67%), and 30 Si (3.1%) are stable. The longest-lived radioisotope is 32 Si, which is produced by cosmic ray spallation of argon.
Here are some values of the ratio of atomic mass to mass number: [10] Nuclide Ratio of atomic mass to mass number 1 H: 1.007 825 031 898 (14) 2 H: 1.007 050 888 9220 ...
For 12 C, the isotopic mass is exactly 12, since the atomic mass unit is defined as 1/12 of the mass of 12 C. For other isotopes, the isotopic mass is usually within 0.1 u of the mass number. For example, 35 Cl (17 protons and 18 neutrons) has a mass number of 35 and an isotopic mass of 34.96885. [7]
The molar mass of atoms of an element is given by the relative atomic mass of the element multiplied by the molar mass constant, M u ≈ 1.000 000 × 10 −3 kg/mol ≈ 1 g/mol. For normal samples from Earth with typical isotope composition, the atomic weight can be approximated by the standard atomic weight [ 2 ] or the conventional atomic weight.
Argon Krypton Xenon Radon Oganesson; Solar System (for each atom of silicon) [20] 2343: 2.148: 0.1025: 5.515 × 10 −5: 5.391 × 10 −6 – – Earth's atmosphere (volume fraction in ppm) [21] 5.20: 18.20: 9340.00: 1.10: 0.09 (0.06–18) × 10 −19: 0 Igneous rock (mass fraction in ppm) [12] 3 × 10 −3: 7 × 10 −5: 4 × 10 −2 – – 1 ...
Atomic numbers are sometimes capped at 92 . [20] Definitions based on atomic number have been criticised for including metals with low densities. For example, rubidium in group (column) 1 of the periodic table has an atomic number of 37 but a density of only 1.532 g/cm 3, which is below the threshold figure used by other authors. [21]