Phosphorus Element Properties and Information
Phosphorus Element Properties and Information:
Phosphorus Element Properties and Information:
Phosphorus is fifteenth element on the periodic table. Elements are arranged in the periodic table on the basis of the atomic number. Atomic number is the number of protons in the nucleus of the atom. Phosphorus has an atomic number of 15. It is located in the Group 15 and Period 3 of the periodic table of elements. It is denoted by P. The name is derived from the Greek word ‘Phosphoros’ meaning Bringer of Light.
Henning Brandt was the first to make phosphorus in 1669 by evaporating urine and heating the residue until it became red hot. The phosphorus vapour distilled in the process which he collected by condensing it in water.
Phosphorus is widely found in different minerals in combined form, it is not found uncombined in nature. The concentration of phosphorus in earth’s crust is about one gram per kilogram. A very important source of phosphorus is the phosphate rocks which contain the apatite minerals.
Physical Properties:
- The two main forms of phosphorus are; white phosphorus and red phosphorus. White phosphorus is a poisonous waxy solid and red phosphorus is an amorphous non-toxic solid.
- The atomic mass of phosphorus is 30.973
- The melting point of phosphorus is 44.2°C
- The boiling point of phosphorus is 280°C
- The density of phosphorus is 1820 in S.I. units at 20°C
- There are 23 known isotopes of phosphorus ranging from phosphorus-25 to phosphorus-47. Among all the isotopes only phosphorus-31 is stable and is makes up approximately 100% of the phosphorus.
- White phosphorus glows in dark when exposed to air with a faint tinge of green and blue.
Chemical Properties:
- Phosphorus is highly reactive this it is not found in nature in uncombined state.
- Due to the action of light and heat the white phosphorus changes to red phosphorus.
- All samples of white phosphorus contain some red phosphorus. In those samples where the discoloration is more apparent, they will appear yellow. Hence impure white phosphorus is also called as yellow phosphorus.
- White phosphorus is pyrophoric or self-igniting in the presence of air.
- White phosphorus is insoluble in water but soluble in carbon disulfide.
- Red phosphorus is comparitively more stable than white phosphorus.
- Violet phosphorus is obtained by prolonged annealing of red phosphorus above 550°C.
- Black phosphorus is obtained by heating white phosphorus under pressures of 1.2 GPa. Black phosphorus is the most stable and least reactive allotrope of phosphorus below 550°C.
Methods of Production:
- Phosphate Rocks: Commercially used method to make elemental phosphorus is to heat phosphate rocks or calcium phosphates to 1200-1500°C with sand which is mostly silicon dioxide and refined coal to produce vaporised phosphorus. The vapours are condensed under water to prevent its oxidation in air but some white phosphorus still gets converted to red phosphorus.
- Bone Ash: Historically, bone ash was used to isolate elemental phosphorus. In this process the tricalcium phosphate in the bone ash was first converted to monocalcium phosphate using sulfuric acid. Monocalcium phosphate was then dehydrated to its corresponding metaphosphate. The metaphosphate was ignited at about 1300°C with charcoal to produce white phosphorus. White phosphorus amounting to two-thirds of the weight of the metaphosphate was produced. Rest of the one-third of the phosphate was present as calcium orthophosphate.
Relevance in Chemical and Related Industries:
- Fertilizer industries: By far the largest use of phosphorus is for making fertilizers because phosphorus is an essential plant nutrient. Fertilizers generally contain about 70-75% of phosphorus pentoxide.
- Organophosphorus: White phosphorus is widely used to make organophosphorus compounds through phosphorus chloride and sulfides intermediates. Organophosphorus compounds are used in plasticisers, flame retardants, pesticides, extraction, and water treatment.
- Metallurgical industries: During smelting process oxygen is present as an impurity with copper, phosphorus is added to react with the oxygen and result in phosphorus containing copper alloy which has high hydrogen embrittlment than normal cooper. Phosphorus is important for steel production, making phosphor bronze.
- Traces: Phosphorus-32 and phosphorus-33 are used as radioactive tracers in biochemical laboratories.
Relevance in Other Industries:
- Military: White phosphorus has applications as incendiary bombs; they are used in smoke bombs, smoke pots, hand grenades and snake screens.
Health Effects on Exposure:
- White phosphorus: Contact with white phosphorus with skin causes the skin to burn. If it is ingested then it causes stomach cramps, nausea and dizziness. Increased concentration is capable of damaging lungs, heart and kidneys and causing death.
- Intake as food: Too much use of fertilizers has introduced a lot of phosphorus in crops. If intake of phosphorus is too much then it affects lungs, kidneys and also bones. Too much phosphorus causes osteoporosis.
Effects on Surroundings:
- Accumulation: White phosphorus can enter air through industries but being quite reactive it gets converted to less harmful substance. This white phosphorus can enter soil and accumulate in the soil and remain for a long period of time as it is not quite mobile in soil. It can enter water bodies and accumulate in the waters and affect aquatic life. If it enters ground water then it can remain there for thousands of years.
- Eutrophication: Accumulation of phosphorus on the water surfaces leads to growth of water dependent life forms such as algae and duckweed, other life forms may not be able to live in such conditions.
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