Allotropic forms : Phosphorus has several allotropes among which the following are important :
I. White phosphorus : It’s a translucent white waxy solid. Its properties are as follows:
1.It is poisonous.
2. It is insoluble in water but soluble in carbon disulphide.
3. It glows in dark and this characteristic is called chemiluminescence.
4. White phosphorus is more reactive than other allotropes in the solid state due to angular strain in P4 molecule in which the bond angle is 600 and so it is less stable.
II. Red Phosphorus : When white phosphorus is heated at the temperature level of 573K for several days, we get red phosphorus. It has following properties:
1. Red phosphorus is a solid with iron grey lustre.
2. It’s odourless and non poisonous.
3. It is non soluble in water as well as carbon disulphide.
4. It doesn’t glow in dark.
5. Red phosphorus is much less reactive than white phosphorus.
6. It is polymeric which contains 4 phosphorus atoms in a chain like structure.
II. Red Phosphorus : When red phosphorus is heated under high pressure, a series of phases of black phosphorus are formed. Its properties are as follows:
1. It has two forms α-black & β-black. α-black phosphorus is formed when red phosphorus is heated in a sealed tube at the temperature level of 803K. β-black phosphorus is formed by heating white phosphorus under high pressure at 473K.
2. It doesn’t burn in air upto 673K.
3. It sublimes in air .
Compounds of phosphorus :
1. PH3-Posphine : Phosphine (IUPAC name: Phosphane) is a poisonous gas which was discovered Gembre in 1783.
Preparation : When calcium phosphide is treated with water or dilute HCl, phosphine is produced.
Ca3P2 + 6H2O → 3Ca(OH)2 + 2PH3
Ca3P2 + 6HCl → 3CaCl2 + 2PH3
Elements in 15th group are known as ‘The Nitrogen Family’. The family includes the following elements:
|Element||Atomic Number||Electronic Configuration||Character|
|Bi||81||1s22s22p63s23p6 3d104s24p64d10 4f145s25p65d106s26p3||Metal|
Occcurence : Nitrogen – Nitrogen is found in the molecular form in the atmosphere. It comprises 75% by mass and 78% by volume of the atmosphere. It is also found in Earth’s crust in the form of Chile Saltpetre(Sodium Nitrate : NaNO3) and Indian Saltpetre(Potassium Nitrate-KNO3). In the form of protein, Nitrogen is also available in plants and animals.
Reactivity towards oxygen : Group 15 elements form oxides by reacting with oxygen of the form E2O3, E2O4 and E2O5 .Ex: N2O3, N2O4, P2O5, As2O5 etc.
Key Points : 1. Among oxides the acidic nature increases with increase in the oxidation state.
2. The acidic nature also increases with increase in the percentage of oxygen.
3. In the group, the acidic nature decrease with increase in atomic number due to increase in the metallic character.
E2O3 Type Oxides of
Nitrogen & Phosphorus
Arsenic & Antimony
4. The stability of oxides decreases down the group.
Reactivity towards Hydrogen : Group 15 elements react with Hydrogen to form hydrides of the form EH3. Ex : NH3 (Ammonia), PH3 (Phosphine), BiH3 (Bismuthine) etc.
Key Points : 1. The thermal stability decreases down the group because the tendency to form covalent bond decreases as the size of atoms increases which leads to increase in the metallic character.