Phosphorous- Allotropic Forms - Infinity Learn by Sri Chaitanya

Phosphorus comes in numerous allotropic forms, the most prevalent of which are white, red, and black Phosphorus. Allotropes are structural variations of an element in which the atoms are bound differently. White phosphorus is the least stable, most reactive, most volatile, least dense, and most poisonous of the allotropes. Scarlet phosphorus has physical characteristics similar to red phosphorus and chemical properties similar to white phosphorus.

Overview:

Allotropy refers to the presence of an element in more than one physical configuration. Allotropes are several physical kinds of a similar element. Allotropes have different physical features but similar chemical properties.

Phosphorus is an important element in chemistry, and it is mostly derived through phosphates, which are molecules that contain the phosphate ion PO₃^4-_. Phosphates may be found in ATP, DNA, RNA, and phospholipids, all of which are necessary components of cells. Human urine was the oldest source of elemental Phosphorus, and bone ash was an important early supply of phosphate.

Allotropes are structural variations of an element in which the atoms are bound differently. Phosphorus is allotropic. Phosphorus comes in a variety of allotropic forms, including white phosphorus, red phosphorus, scarlet phosphorus, metallic orα -black phosphorus, β-black phosphorus, and violet phosphorus.

However, the most prevalent allotropic forms of phosphorus are white, red, and black.

White Phosphorus

White or yellow phosphorus is the most prevalent kind of phosphorus. It is produced by heating phosphate rock, silica, and coke in an electric furnace at 1770 degrees Celsius.

Structure of White Phosphorus

It is available in P₄ units. The four sp³ hybridized phosphorus atoms are arranged in the corners of a regular tetrahedron with an angle PPP=60°. To complete the octet, each phosphorus atom is covalently connected to three other P-atoms. White phosphorous becomes yellow when exposed to light. As a result, it is known as yellow phosphorus.

Properties of White Phosphorus

Physical Properties of White Phosphorus:

It’s a flexible solid. It is practically colourless when newly made, but takes on a pale yellow colour after standing. As a result, it is commonly known as yellow phosphorus. It’s so soft that it can be sliced with a knife.
It smells strongly of garlic.
It is harmful by nature. Phossy Jaw is a condition in which the jawbones of persons who deal with phosphorus degrade.
It dissolves in carbon disulfide and oils but not in water.
Because the numerous P₄ molecules of white phosphorus are only held together by weak van der Waals forces of attraction, the melting point (317k) and boiling point (553k) of white phosphorus are both relatively low.

Chemical Properties of White Phosphorus:

Air action: The angle strain in white phosphorus is really high. As a result, it is extremely reactive. It easily catches fire in the air, producing a greenish-yellow flame that may be seen in the dark. This is known as chemiluminescence or phosphorescence.
When white phosphorus is heated in the air, it becomes very reactive and catches fire. When burnt, it emits dense white phosphorus pentoxide fumes.
It interacts with numerous metals, including Na, K, Mg, Ca, Ag, and others, to generate their respective phosphides.
Reaction with caustic soda: When heated in an inert environment with an aqueous solution of caustic soda, it yields phosphine.
Reduced properties: It is a strong reducing agent. Sulphuric acid is converted to sulfur dioxide, and nitric acid is converted to nitrogen dioxide.

Red Phosphorus

It’s a violet-red powder with tiny crystals and amorphous phosphorus. It is created by heating white phosphorus for several hours at 525 degrees Celsius in an inert environment.

Preparation of Red Phosphorus:

Yellow phosphorus is gathered in an egg-shaped cast iron retort with two thermometer jackets and a tall pipe at the top with a safety valve and feeder.
In small amounts, iodine is also added. Iodine accelerates the conversion of white phosphorus to red phosphorus.
In the retort, an inert gas, such as coal gas or carbon dioxide, substitutes the air. The retort was allowed to cool once it had been heated for the required amount of time. The firm red Phosphorus lump is obtained.
Pulverized white phosphorus is boiled in a caustic soda solution to dissolve any leftover white phosphorus.
The red phosphorus is insoluble. It has been thoroughly cleaned and dried.

Structure of Red Phosphorus:

The polymeric structure of the red phosphorus molecule. It is made up of chains of P4 tetrahedra that are connected together. Because of its polymeric structure, red phosphorus is less reactive than white phosphorus.

Properties of Red Phosphorus:

It has an iron-grey lustre and is a hard, crystalline, odourless solid.
It is not toxic in any way.
It is not soluble in water or organic solvents such as CS2, alcohol, or ether.
Because it is polymeric, it is less reactive than white phosphorus.
It sublimes when heated, creating vapours similar to those generated by white phosphorus. White phosphorus is generated when these vapors condense. This is a simple method for turning red phosphorus into white phosphorus.
Because it is less reactive than white phosphorus, when heated, it only forms salts with halogens, sulfur, and alkali metals.
When burnt with oxygen at 565 degrees Celsius, it yields phosphorus pentoxide.
Caustic alkalies have no effect on it. This property is used to differentiate between red and white phosphorus.
It is a moderately stable phosphorus allotrope at room temperature. It has a substantially higher ignition temperature than white phosphorus (543k) (303k). As a result, it does not burn readily.
It is a poor electrical conductor and has a greater density (2.16gcm^–3) than white phosphorus (1.84gcm^–3).

Black Phosphorus

Black Phosphorus are of two types:

Metallic or α-black Phosphorus

This sort of black phosphorus is created by dissolving red phosphorus in the molten lead for an extended period of time in a sealed tube at 400°C. When the mixture cools, black phosphorus crystals develop. The lead is dissolved by mild nitric acid treatment. It is an exceptionally stable phosphorus allotrope that does not oxidize in the air unless it is very hot. It is not an electrical conductor.

β- Black Phosphorus

It is made by heating white phosphorus at 473 degrees Celsius under extremely high pressure (about 4000–12000 atm). It may also be made by heating white phosphorus at 220–370°C for 7–8 days under mercury pressure, which works as a catalyst. This is the only kind of phosphorus whose structure is certain.

Structure of Black Phosphorus

It is crystalline and composed of corrugated sheets, with each phosphorus atom covalently bound to three neighboring phosphorus atoms. The P–P angles are 99 degrees. The P–P distance between the two phosphorus atoms closest to each other is 2.18A°.

Properties of Black Phosphorus

The following are the general qualities of black phosphorus:

It comes in three crystalline and one amorphous variety.
α-black phosphorus is a rather excellent electrical conductor, however -black phosphorus is a non-conductor.
β-black phosphorus has a black metallic lustre.
It is the least reactive and most stable phosphorus type.

Scarlet Phosphorus

By boiling a 10% phosphorus solution in phosphorus tribromide for around 10 hours, this allotrope is formed as an amorphous red powder. Pure crimson phosphorus may be created by heating phosphorus tribromide with mercury at 2400 degrees Celsius. Scarlet phosphorus has physical characteristics similar to red phosphorus and chemical properties similar to white phosphorus.

Violet Phosphorus

Violet phosphorus is made by heating white phosphorus with a trace of sodium under high pressure at 230°C. It has a crystalline structure.

Comparison of the Reactivity of Allotropic Phosphorus Forms

The chemical reactivity of the three allotropic forms of Phosphorus varies greatly. White phosphorus has the highest reactivity, whereas black phosphorus has the lowest. As a result, white phosphorus is stored underwater to keep it safe from air, but red and black phosphorus are stable in the air.

Uses of Allotropes of Phosphorus

Red phosphorus is utilized in the production of matches because it is non-poisonous
Red phosphorus is used to create phosphorus bronze, which is strong, tenacious, and water-resistant.
It is also utilized in the synthesis of chemicals such as phosphorus chlorides, phosphoric acids, and hypophosphites, which are used in industry and medicine.
Rat poison is made from white phosphorus.
Yellow phosphorus is utilized in the production of tracer bullets, incendiary explosives, and smoke screens.

FAQ’s

Q. Which phosphorus allotrope is poisonous?

Ans: White phosphorus is the least stable, most reactive, most volatile, least dense, and most poisonous of the allotropes. It gradually turns to red phosphorus as a result of light and heat.

Q. Why is phosphorus known as the “devil’s element”?

Ans: Phosphorus is referred to as the “Devil’s Element” because of its eerie brilliance, the potential to explode into flames, and since it was the 13th known chemical. Pure phosphorus, like other nonmetals, takes on a variety of forms. There are at least five phosphorus allotropes.

Q. Phosphorus is P4, give a reason.

Ans: Phosphorus can form a P4 white phosphorus tetrahedron because it can establish three bonds, whereas sulfur can only form two. As a result, sulfur only forms rings and chains. The most soluble allotrope of phosphorus, red phosphorus, is a cross-linked polymeric chain of atoms.

Q. What type of phosphorous is used in matchsticks?

Ans: As the match is ignited, a little portion of the red phosphorus on the striking surface is transformed into white phosphorous, which subsequently ignites. The heat from this ignites the potassium chlorate, causing the match head to burst into flame.