Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent non-metal of the nitrogen group, phosphorus is commonly found in inorganic phosphate rocks. Elemental phosphorus exists in two major forms - white phosphorus and red phosphorus. Although the term "phosphorescence", meaning glow after illumination, derives from phosphorus, glow of phosphorus originates from oxidation of the white (but not red) phosphorus and should be called chemiluminescence.
The first form of phosphorus to be discovered (white phosphorus, in 1669) emits a faint glow upon exposure to oxygen — hence its name given from Greek mythology, Φωσφόρος meaning "light-bearer" (Latin Lucifer), referring to the "Morning Star", the planet Venus.
Phosphorus is a component of DNA, RNA, ATP, and also the phospholipids that form all cell membranes. It is, thus, an essential element for all living cells.
Phosphorus has several forms (allotropes) that have strikingly different properties. The two most common allotropes are white phosphorus and red phosphorus. Red phosphorus is an intermediate phase between white and violet phosphorus. Another form, scarlet phosphorus, is obtained by allowing a solution of white phosphorus in carbon disulfide to evaporate in sunlight. Black phosphorus is obtained by heating white phosphorus under high pressures (about 12,000 atmospheres). In appearance, properties, and structure, it resembles graphite, being black and flaky, a conductor of electricity, and has puckered sheets of linked atoms. Another allotrope is diphosphorus; it contains a phosphorus dimer as a structural unit and is highly reactive.
In 1669, German alchemist Hennig Brand attempted to create the philosopher's stone from his urine, and in the process he produced a white material that glowed in the dark. The phosphorus had been produced from inorganic phosphate, which is a significant component of dissolved urine solids. White phosphorus is highly reactive and gives off a faint greenish glow upon uniting with oxygen. The glow observed by Brand was caused by the very slow burning of the phosphorus, but as he neither saw flame nor felt any heat he did not recognize it as burning.
The base value of each unit of ranges between 1 and 10Ð per unit, with up to 3 units being found at any one time.
Presence on Mars: Common
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