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NITROGEN

Nitrogen is a colourless gaseous element, and belongs to the group V of the periodic table. It is diatomic and relatively inert. It occurs in air and is an essential constituent of proteins and nucleic acids. In the combined state it is found as nitrates and ammonium compounds. It is charecterised by

1. Atomic number 7
2. Relative atomic mass 14.0067
3. Density 1.2506 g/dm³
4. It is slightly lighter than air.
5. Melting point -209.86^OC
6. Boiling point 195.8^OC
7. It is a colourless, odourless and a tasteless gas.
8. Like Carbon dioxide, it is neither combustible nor a supporter of combustion, but animals die in it due to the lack of oxygen.

PREPARATION

1. In laboratory it is prepared by the action of heat on ammonium nitrite or ammonium dichromate.

Since ammonium nitrate is an unstable compound thus it is first obtained as an intermediate salt

NH₄Cl + NaNO₂ è NH₄NO₂ + NaCl

NH₄NO_{2 è} N₂ + 2H₂O

(NH₄)₂Cr₂O₇ è N₂ + Cr₂O₃ + 4H₂O

2. By the oxidation of ammonia

8NH₃ + 3Cl₂ è 6NH₄Cl + N₂

_heat

2NH₃ + 3CuO è 3Cu + N₂ + 3H₂O

3. By passing the vapours of nitric acid over strongly heated copper

5Cu + 2HNO₃ è 5CuO + N₂ + H₂O

4. Commercially nitrogen is obtained by the fractional distillation of liquid air.

CHEMICAL PROPERTIES

1. Nitrogen combines with oxygen in the presence of an electric discharge to form nitric oxide

N₂ + O₂ è 2NO

This is a reversible reaction and the temperature required is of the order of 3000^OC (thus an electric spark is used)

2. Nitrogen combines with hydrogen to form ammonia (Haber’s process)

400-500 OC/200 atm

N₂ + 3H_{2 è} 2NH₃

finely divided nickel\

3. red hot metals react with nitrogen to form their nitrides

6Li + N₂ è 2Li₃N

2Al + N₂ è 2AlN

USES

1. Used in the manufacture of ammonia by Haber’s process .
2. To provide an inert atmosphere in welding and metallurgy.
3. In nature it dilutes the action of oxygen and thus may be called ‘a life supporting element’.
4. It is used for filling p electric bulbs.

ANOMALOUS BEHAVIOUR OF NITROGEN

Nitrogen differs from the other members of this group. The anomalous behaviour of nitrogen is basically due to the following properties.

• Small size
• Low electropositive nature and thus a very high electronegativity.
• Lack of d-orbitals in its valence shell.
• Property to form multiple bonds easily.

Some of the main features in which nitrogen differs from the other elements in its group can be stated as below;

1. Nitrogen is a gas whereas all the other members of this group are solids
2. Nitrogen forms a diatomic molecule whereas the other elements of this group form a tetra atomic molecule, due to their inability to form multiple bonds.
3. In its group nitrogen and phosphorous are the only non-metals.
4. Nitrogen has the ability to form hydrogen bonds in its compounds.
5. Nitrogen is chemically inert.
6. Nitrogen can form five oxides ( as N₂O, NO, N₂O₃, NO₂ and N₂O₅) whereas the other elements in this group can form at the most three oxides.

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