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Arsenic is a chemical element with the symbol As and the atomic number 33. It is a metalloid and one of the pnictogens , and therefore shares many properties with its group 15 neighbors phosphorus and antimony .
Atomic number (Z): 33: Group: group 15 (pnictogens) Period: period 4: Block p-block Electron configuration [] 3d 10 4s 2 4pElectrons per shell: 2, 8, 18, 5: Physical properties; Phase at STP
A chemical element, often simply called an element, is a type of atom which has a specific number of protons in its atomic nucleus (i.e., a specific atomic number, or Z). [ 1 ] The definitive visualisation of all 118 elements is the periodic table of the elements , whose history along the principles of the periodic law was one of the founding ...
Tungsten (also called wolfram) [14] [15] is a chemical element; it has symbol W and atomic number 74. It is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a distinct element in 1781 and first isolated as a metal in 1783.
The soils hold 1 to 10 parts per million of arsenic, and seawater carries 1.6 parts per billion of arsenic. Arsenic comprises 100 parts per billion of a typical human by weight. Some arsenic exists in elemental form, but most arsenic is found in the arsenic minerals orpiment, realgar, arsenopyrite, and enargite. [14]
Arsenic is attacked by nitric acid and concentrated sulfuric acid. It reacts with fused caustic soda to give the arsenate Na 3 AsO 3 and hydrogen gas. [333] Arsenic sublimes at 615 °C. The vapour is lemon-yellow and smells like garlic. [334] Arsenic only melts under a pressure of 38.6 atm, at 817 °C. [335]
This led to the nuclear charge, or atomic number of an element, being used to ascertain its place within the periodic table. With this method, Moseley determined the number of lanthanides and showed that there was a missing element with atomic number 72. [7] This spurred chemists to look for it. [8]
Whereas the mass number simply counts the total number of neutrons and protons and is thus an integer, the atomic mass of a particular isotope (or "nuclide") of the element is the mass of a single atom of that isotope, and is typically expressed in daltons (symbol: Da), or universal atomic mass units (symbol: u).