Nitrogen was discovered in 1772 by Daniel Rutherford, a Scottish scientist. Lavoisier established its elemental nature and named it azote. The present name nitrogen is derived from nitre which is a well known nitrogenous compound. Nitrogen is the first element of group 15 of the periodic table and has electronic configuration 1s22s22p3. The molecular form of nitrogen is referred to as N2. The method of preparation of nitrogen and N2 (Dinitrogen) is the same. They have the same physical and chemical properties as well as uses. Nitrogen is an essential constituent of all vegetable and animal proteins which are vital for life processes.
In the laboratory, N2 is prepared by heating an aqueous solution of ammonium chloride and sodium nitrite.
NH4Cl(aq)+NaNO2(aq) → NaCl(aq)+2H2O(l)+N2(g)
Small amounts of nitric oxide and nitric acid are also formed in this reaction. The N2 thus obtained is purified by passing the evolved gas through an aqueous sulphuric acid solution containing potassium dichromate.
By Thermal Decomposition of Ammonium Dichromate
When red crystals of ammonium dichromate are heated, a violent reaction takes place which is accompanied by flashes of light and evolution of nitrogen.
(NH4)2Cr2O7 → N2+4H2O+Cr2O3
By Oxidation of Ammonia
When ammonia is oxidized by a red hot copper oxide or by chlorine, nitrogen is obtained.
2NH3+3CuO → N2+3H2O+3Cu
8NH3+3Cl2 → N2+6NH4Cl
By Thermal Decomposition of Sodium Azide
Very pure nitrogen can be obtained by heating sodium or barium azide.2NaN3 → 2Na+3N2
Ba(N3)2 → Ba+3N2
Commercially, N2 is prepared by the fractional distillation of liquid air.
Physical Properties of Dinitrogen (N2)
It is a colourless, odourless, and tasteless gas.
It is non-poisonous but animals die in an atmosphere of nitrogen for want of oxygen.
It has very low solubility in water (23.2 cm3 per litre of water at and pressure)
It’s melting and boiling points are 63.2K and 77.2K respectively.
Chemical Properties of Dinitrogen (N2)
N2 is almost non-reactive at ordinary temperatures. It neither burns nor supports combustion. The chemical inertness of N2 at ordinary temperatures is due to the high stability of the molecule.
In a molecule of N2, the two nitrogen atoms are linked together by a triple bond. The triple bond has a very high bond enthalpy(amount of heat energy required to break a chemical bond) . Due to very high bond dissociation enthalpy, N2 is almost unreactive towards most of the reagents.
However, at high temperatures, it combines with some metals and non-metals to form ionic and covalent compounds called nitrides. Some important chemical reactions of N2 are given below.
N2 combines with some highly electropositive metals at high temperatures forming their nitrides. Lithium nitride forms slowly at ordinary temperatures but rapidly at higher temperatures. Magnesium and aluminum continue burning in an atmosphere of nitrogen forming their nitrides. Calcium, strontium, and barium react with N2 when they are red hot.
2Al+N2 → 2AlN
Combination with O2
N2 combines with O2 in presence of electric arc (above 3273K) to form nitric oxide.
What Happens When N2 Combines with H2?
N2 reacts with H2 at 725K under a pressure of 200 atmospheres in presence of a catalyst (finely divided iron and molybdenum).
Write Chemical Equations for The Reaction of N2 with Alumina and Calcium Carbide.
Al2O3+N2+3C → 2AlN+3CO
CaCN2 or Calcium cyanide is an important fertilizer.
The main use of N2 is in the manufacturing of ammonia. It is also used in the preparation of some other important chemicals such as calcium cyanide, nitric acid, etc.
It is used for providing an inert atmosphere in several metallurgical operations.
Liquid nitrogen is used as a refrigerant to preserve biological materials and in freezing food articles. It is also used in cryosurgery.
It is used as an inert diluent for reactive chemicals.
1. How does nitrogen differ from other elements of the group?
Nitrogen differs from the other elements of the group in several aspects like:
At ordinary temperatures, nitrogen is a gas while all other elements of the group are solids.
Nitrogen exists as a diatomic molecule while phosphorus and other elements of the group exist as tetratomic molecules.
Due to its small size and high electronegativity, nitrogen is the only element of the group which can form hydrogen bonds in its compounds.
Due to the absence of d-orbitals, nitrogen does not form complexes. The other elements of the group undergo complex formation.
Nitrogen does not form pentahalides, while all other elements of the group form pentahalides.
2. State the conditions necessary for the formation of ammonia from nitrogen.
The conditions necessary for the formation of ammonia from nitrogen are:
The low temperature of 720K-770K: Since the reaction is exothermic, low temperature favors the reaction to proceed in the forward direction giving a higher yield of ammonia.
High pressure of 200 atmospheres: Since the reaction proceeds with a decrease in volume, a higher yield of ammonia can be obtained at high pressures.
Catalyst: To increase the rate of reaction, a catalyst like finely divided iron with molybdenum as a promoter is used.