Phosphorus: Introduction, History, Types

Phosphorus is the 12th most abundant element on the Earth's Crust bearing the symbol P and having the Atomic Number as 15. Phosphorus is present in the form of one atom for every 100 atoms of silicon making it one of the least abundant elements in the universe accounting for only 0.0007% of all matter. 

Also read: Group 15 Elements

Key Terms: Phosphorus, White Phosphorus, Red Phosphorus, Phosphorus Cycle, Uses of phosphorus

Read Also: Class 12 Dinitrogen

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What is Phosphorus?

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Phosphorus is a multivalent non-metallic chemical element and it belongs to the Nitrogen family which is the Group 15 [Va] in the periodic table. It is the 12th most abundant element on the crust of the Earth and it mostly does not occur in free state due to its high chemical reactivity. 

The most vital source of Phosphorus is phosphorite or the phosphate rock. Western Sahara and Morocco account for containing up to 80% of the total Phosphate rock on the Earth’s crust which approximately sums up to 65,000,000,000 tons.

Phosphorus

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Chemical Properties of Phosphorus

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• Atomic Number – 15
• Period – 3
• Block – P
• Atomic Mass – 30.9738 g mol^-1
• Oxidation States - ±3,4,5
• Density – 1.823 g cm-3
• Melting Point – 44.1°C (111.4°F)
• Boiling Point – 280°C (536°F)
• Electronic Configuration – 1s²2s²2p⁶3s²3p³
• Key Isotopes – 31P
• Allotropes – White P, Red P, Black P, P2
• Crystal Structure – Body Centred Cubic (BCC)
• Bond Enthalpies –

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Types of Phosphorus

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The two main forms of Phosphorus are – White Phosphorus and Red Phosphorus.

White Phosphorus

White Phosphorus, also called tetra-Phosphorus exists in P4 state which means that it exists as the molecules made up of four atoms in a tetrahedral structure. White Phosphorus is waxy in nature and becomes yellow quickly when it is exposed to a light source. It glows green when exposed to oxygen, highly flammable and ignites when it comes in contact with air. It is extremely toxic. 

White Phosphorus

Production: In industrial production, Phosphate rock is heated in a furnace with carbon and silica. This produces elemental Phosphorus as a vapor which is collected under phosphoric acid. The equation is as follows:

2Ca₃(PO₄)₂ + 6 SiO₂ + 10C →6CaSiO₃ + 10CO + P₄

Applications: White Phosphorus is used in industries to produce fertilizers and cleaning compounds. It was used as pesticides and in fireworks. Since it is flammable, it is used as a form of ammunition in the military. It can be used as a smoke agent since it produces clouds of white smoke

Red Phosphorus

Red Phosphorus is the most common and concentrated source of Phosphorus. It is polymorphic in nature having a deep red color and a sort of grey luster. It is a derivative of the P4 molecule where one of the P-P bonds is broken. It is non-toxic and less reactive than the white Phosphorus. Red Phosphorus can react with water vapors and oxygen. Upon reaction, it forms phosphine gas, Phosphorus oxyacids and phosphoric acid.

Red Phosphorus

Production: White Phosphorus was very unstable and was kept underwater to avoid catching fire. A more stable form of phosphorus, Red Phosphorus, was discovered when white Phosphorus was heated to 482F and the process was continued for 2 days. 

Temperature was increased to 673K to filter residue white Phosphorus. In this process, water is removed from the mixture and sodium carbonate is added. The mixture is vacuum dried. Another way to obtain Red Phosphorus is reduction of animal bones to ash and treatment with phosphoric acid and calcium sulfate. 

Applications: Red Phosphorus is used extensively in the production of fertilizers, pesticides, semiconductors, matches, etc. It is also known to be used in electroluminescent coatings and several organic reactions. It is stable but reactive hence used in safe matches and smoke bombs.

Also, read: Electronegativity

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Uses of Phosphorus

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1% of the total body-weight of a person is Phosphorus. It is very essential in the formation of bones and teeth. It is essential to use carbohydrates and fats in the body. It works with vitamin B helping with kidney functions, normal heartbeat and nerve signaling. It is also needed to form protein.

Foods that are rich in Phosphorus are –

• Chicken
• Turkey
• Organ Meats
• Seafood
• Dairy
• Whole Grains
• Beans and Lentils
• Soy
• Quinoa

Phosphorus is also very important for key functions in plants like photosynthesis, transformation of sugars and starches, movement of nutrients in plants, etc. Its deficiency can have adverse effects on the growth of the plant. In the human body, it is vital for maintaining normal pH in the blood. Hormones contain Phosphorus as the structural component. 

Other Uses of Phosphorus

• Phosphorus is a very important nutrient for plants and is utilized in the form of phosphate compounds. A lot of fertilizers therefore contain phosphate compounds to fill this necessity. There exists a phosphate cycle just like how carbon and nitrogen cycle exist.
• It is used in the manufacturing process of steel and also phosphate bronze.
• Some detergents also contain Phosphorus.
• Manufacturing of Light Emitting Diodes include Phosphorus.

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Phosphorus Cycle

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Phosphorus cycle describes how Phosphorus is circulated throughout nature. Phosphorus circulation is very scarce when compared to the circulation of other elements. Phosphorus is mostly found as phosphate ions which are contained in rocks and sediments.

There are 4 main steps in a Phosphorus Cycle, namely:

1. Weathering: Phosphorus is mostly found in rocks and other sediments. It exists in the form of phosphate salts. These salts are removed from these rocks and sediments through weathering which is then absorbed into the soil. This can happen due to changes in temperature, water, animals or other agents that cause weathering.
2. Absorption through plants: After weathering, these phosphate salts are absorbed into the soil which are in turn absorbed by the plants. Since the absorption of Phosphorus is very less, the practice of using fertilizers containing Phosphorus is quite common among farmers.
3. Absorption through animals: Animals ingest Phosphorus by consuming these plants that absorbed Phosphorus after weathering.
4. Decomposition, bringing it back to the environment: After the death of these animals and plants, microorganisms decompose their remains where the organic form of Phosphorus gets converted to an inorganic form, therefore returning back to earth. Once absorbed into the soil, Phosphorus gets back into rocks and sediments. Hence, the cycle repeats.

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Things to Remember

• Phosphorus is a nonmetallic chemical element whose symbol is P and atomic number is 15.
• The two major forms of Phosphorus are White Phosphorus and Red Phosphorus.
• White Phosphorus was discovered by Hennig Brandt in 1669. It is waxy in nature, highly flammable and unstable. 
• Red Phosphorus is a more stable allotrope of Phosphorus. It has a deep red color. It is less reactive and toxic when compared to White Phosphorus. It is mostly used to make safe matches, semiconductors, etc. It cannot be dissolved in water and carbon disulfide.
• At 20°C Phosphorus is in solid state. Its key isotope is 31P.
• Phosphorus is essential for the production of steel. It is found in foods like beans, chicken, seafood, etc.
• It is vital for the healthy growth of bones, teeth, muscles and kidneys.
• Phosphorus combines directly with a number of halogens and forms phosphides when heated with metal.

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