phosphorus

phosphorus
Name	phosphorus
Number	15
Category	nonmetal
Group	15
Standard atomic weight	30.973761998(5)
Electron configuration	[Ne] 3s2 3p3
Phase	solid
Melting point c	44.15
Boiling point c	280.5
Density g cm3	white: 1.823, red: ~2.2–2.34, black: 2.69
Appearance	white, red, violet, black

phosphorus is a chemical element essential to all known forms of life on Earth. It was first isolated in 1669 by the alchemist Hennig Brand through the distillation of human urine, a discovery that marked a significant moment in the history of chemistry. The element exists in several major allotropes, most notably white, red, and black phosphorus, each with distinct properties and reactivities. Its high reactivity means it is never found as a free element in nature but is a key component of minerals such as apatite and is a fundamental building block in molecules like adenosine triphosphate (ATP) and deoxyribonucleic acid (DNA).

Properties

Phosphorus exhibits notable allotropy, with white phosphorus consisting of P₄ molecules that are highly reactive, pyrophoric, and extremely toxic, glowing faintly upon exposure to oxygen in a process known as chemiluminescence. In contrast, red phosphorus, a more stable polymer, is formed by heating white phosphorus and is used in safety matches, while black phosphorus, the most stable allotrope, has a layered structure similar to graphite and exhibits semiconductor properties. The element sits below nitrogen in group 15 of the periodic table, sharing a common valence electron configuration but displaying significantly different chemistry, including the ability to form strong covalent bonds with itself and other elements like oxygen and hydrogen.

Occurrence and production

Due to its reactivity, elemental phosphorus is not found freely in the Earth's crust but is bound in phosphate rock minerals, primarily fluorapatite and hydroxyapatite. Major deposits of these phosphate ores are mined extensively in countries like Morocco, China, the United States, and Russia. The primary industrial method for producing elemental phosphorus is the electric arc furnace process, where phosphate rock is mixed with silica and coke and heated to high temperatures, yielding phosphorus vapor that is condensed under water. Historically, the Guano deposits on islands like Nauru were a significant source of phosphates before the large-scale development of rock phosphate mining.

Compounds

Phosphorus forms a vast array of important compounds, most notably involving oxygen in various oxidation states. Phosphoric acid (H₃PO₄), produced via the wet process or the thermal process, is a crucial industrial chemical used in fertilizers and cola beverages. Organophosphorus compounds include vital biomolecules such as phospholipids for cell membranes and phosphate esters in DNA, as well as synthetic pesticides like malathion and nerve agents such as sarin. Inorganic compounds range from phosphine (PH₃), a toxic gas, to phosphorus pentoxide (P₄O₁₀), a powerful desiccant.

Biological role

Phosphorus is indispensable in biology, forming the backbone of nucleic acids like DNA and RNA and serving as the primary energy currency of cells through molecules like ATP and creatine phosphate. It is a key component of hydroxyapatite, the mineral that strengthens bones and tooth enamel, and of phospholipid bilayers that constitute cell membranes. The element cycles through ecosystems via the phosphorus cycle, which involves the weathering of rocks, uptake by plants and microorganisms, and transfer through the food web, with availability often being a limiting nutrient in many aquatic ecosystems like Lake Erie.

Applications

The dominant use of phosphorus, accounting for about 90% of production, is in agriculture as various phosphate fertilizers such as triple superphosphate and diammonium phosphate to enhance crop yields. White phosphorus was historically used in matches and incendiary weapons like white phosphorus smoke screens, while red phosphorus is a key component in the striking surface of safety matches. Organophosphorus compounds are widely employed as plasticizers, flame retardants in materials, ligands in coordination chemistry, and active ingredients in herbicides and insecticides. Black phosphorus is also being researched for potential use in advanced electronics and optoelectronics.

Safety and environmental aspects

White phosphorus is highly toxic and poses severe hazards, causing chemical burns upon contact and organ failure if ingested, with its military use controversial under protocols like the Geneva Convention. Environmental concerns primarily stem from eutrophication, where runoff of phosphate fertilizers into water bodies leads to excessive algal blooms, hypoxia, and dead zones, as seen in the Gulf of Mexico. Regulations such as the Clean Water Act in the United States aim to control nonpoint source pollution from agriculture, while industrial hygiene standards set by organizations like OSHA limit workplace exposure to phosphorus compounds.

Category:Chemical elements Category:Pnictogens Category:Dietary minerals