Some facts about Dinitrogen

Nitrogen is a p-block element present in group 15 or VA and period 2nd. It is represented by the formula N2. It is the major constituent of the atmosphere, approximately 78% by volume. It is the seventh most unreactive molecule in the universe due to the presence of triple bonds between two nitrogen atoms. Dinitrogen is a colourless and odourless diatomic gas. The human body comprises nearly 3 percent nitrogen by mass and is one of the basic components of all living organisms. Majorly, it is composed of amino acid, nucleic acid (DNA and RNA), and ATP (adino triphosphate). 

Structure of Dinitrogen

A molecule of dinitrogen is diatomic as it contains two similar nitrogen atoms (N) which are bonded together with the help of triple bonds (a triple bond consists of 1 and 2 bonds). A Nitrogen atom consists of 5 electrons in the outermost shell , 2 electrons in 2s orbital, and 3 unpaired electrons in 2p orbital. The two nitrogen atoms are bonded with 3 covalent bonds, providing stability and inertness to a dinitrogen molecule.

The structure of dinitrogen can be studied with the help of the Lewis dot structure. The structure of dinitrogen is symmetric and non-polar in nature. The molecules which are small and non-polar tend to be gaseous in nature, hence the gaseous nature of dinitrogen can be justified.

Preparation of Dinitrogen

• In lab 

NH4Cl + NaNO2                 N2 + 2H2O + NaCl

The reaction of 1 molecule of ammonium chloride with 1 molecule of sodium nitrite in the presence of heat leads to the formation of 1 molecule of dinitrogen, 2 molecules of water, and 1 molecule of sodium chloride.

• By thermal decomposition of barium azide

               Ba(N3)2     Ba + 3N2

By the thermal decomposition of barium or sodium azide, dinitrogen in the purest form can be obtained. 

• Commercially

It is prepared by a 2-step process which includes the liquefaction and fractional distillation of liquid air. 

1. Liquefaction

High pressure (100 to 200 atm) is applied to reduce air into liquid air form. The air gets compressed and has to be passed through a jet, allowing it to expand. In order to get liquid air, the process has to be repeated again and again.

2. Fractional Distillation

Liquid air consists of oxygen and nitrogen. The boiling point of nitrogen is lower than that of oxygen, and hence, it can be distilled first; oxygen remains in the liquid air mixture. Distilled out nitrogen can further be obtained by purifying it.

• Thermal decomposition of ammonium dichromate

(NH4)2Cr2O7      →   Cr2O3 + N2 + 4H2O                        

Ammonium dichromate decomposes thermally into chromic oxide, dinitrogen, and water molecules.  

Physical Properties of Dinitrogen

1. Colourless

2. Odourless

3. Tasteless

4. Non-toxic

5. Inert at room temperature

6. Diamagnetic nature

7. Sparingly soluble in water

8. Less dense than air and vapour density=4

9. Low melting and boiling points

10. Has stable isotopes- 14N and 15N

11. Upon condensation, dinitrogen can be converted into colourless gas which upon solidification can form snow-like mass.

Chemical Properties of Dinitrogen

Dinitrogen is unreactive at lower temperatures, but it becomes reactive as the temperature increases. Inertness is due to high bond dissociation enthalpy due to the presence of triple bonds. At higher temperatures, it can react with metals and non-metals to form ionic and covalent compounds respectively. Some of its chemicals actions are as follows:

1. With litmus

No action of dinitrogen on litmus paper as dinitrogen is neutral, hence showing no effect.

2. With metals

Dinitrogen reacts with alkali and alkaline earth metals to form nitrides as follows:

6Li + N2       2Li3N

2Al + N2           2AlN

3Ca + N2         Ca3N2

3Mg + N2        Mg3N2

3. With non-metals

• With hydrogen (Haber’s Process)

The process takes place under temperature 700K and pressure of 200 atm; iron acts as a catalyst and molybdenum acts as a promoter. Nitrogen reacts with hydrogen to produce ammonia.

N2 + 3H2 2NH3

• With oxygen

When oxygen reacts with nitrogen, nitric oxide is produced. The nitric oxide produced is very unstable and immediately reacts with excess oxygen and produces nitrogen dioxide. The process takes place under high temperature (2000K) conditions or where lightning can also be used.

N2 + O2   2NO 2NO + O2 2NO2

4. With compounds

• With calcium carbide-

CaC2 + N2 CaCN2 + C

On strong heating, calcium carbide is heated with dinitrogen and produces calcium cyanamide. When calcium cyanamide is hydrolysed, it releases ammonia which serves as a function of fertiliser in agriculture. Calcium cyanamide is used as a fertiliser under the name of Nitrolim.

Uses

Dinitrogen can be used in the following ways:

1. Food industry – It is used as a preservative and refrigerant.

2. Iron and steel manufacturing industries – Dinitrogen helps to create an inert atmosphere.

3. Synthesis of compounds – Nitric acid, ammonia, nitrides, nitric oxide, and nitrous oxide.

4. Manufacturing of fertilisers – Synthesis of calcium cyanamide (used as fertiliser).

5. Gas-filled thermometers – They are used to measure high temperature.

6. It is used to preserve biological samples at lower temperatures which is known as cryopreservation.

Conclusion

Dinitrogen is a compound of nitrogen which has great importance. It is present in the air that we breathe. Dinitrogen helps in the synthesis of compounds like ammonia and nitric acid. The reaction of dinitrogen with calcium carbide leads to the synthesis of nitrolim (fertiliser). Dinitrogen is used in the food and manufacturing industries. Due to its properties like non-reactivity and inertness, it can be used in the bio-preservation of samples and specimens. Dinitrogen under special conditions of temperature and pressure can be synthesised in the lab as well as on a commercial scale.