Tag Archives: Nitrogen family

Phosphorus & Its Compounds

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

The Nitrogen Family

Elements in 15th group are known as ‘The Nitrogen Family’. The family includes the following elements:

Elements

Symbol State

Metallic Properties

Nitrogen

N Gas Non-metal
Phosphorus P Solid

Non-metal

Arsenic

As Solid Metalloid
Antimony Sb Solid

Metalloid

Bismuth

Bi Solid 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.

Phosphorus : Minerals of the apatite family are main source of phosphorus as flourapatite : Ca9(PO4)6.CaX2 where X =F, Cl and Br. In the animal and plant matter nitrogen is an essential component. It is also found in bones of animals. As phosphoproteins it is available in milk and eggs.

Arsenic, Antimony & Bismuth : They are found in sulphide minerals.

Properties of 15th group elements :

Atomic properties :

● Electronic configuration : The electronic configuration of the outermost shell is ns2np3. Due to half filled p orbital these elements are quite stable.

Atomic & ionic radio :

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

Nature

Nitrogen & Phosphorus

Purely acidic

Arsenic & Antimony

Amphoteric

Bismuth

Basic

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.

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