Daniel Rutherford, a Scottish Physician, discovered Nitrogen in 1772. But it was Lavoisier, who proved that nitrogen is an element and that it was not a supporter of combustion and respiration. He called it 'azote' meaning 'no life'. The name 'Nitrogen' was given to it by Jean Antoine Chaptal (1756 - 1832), in the year
1790.

1. Nitrogen exists in the free and in the combined form in the atmosphere of the earth.
2. In the free state it occurs as N₂ and occupies about 80% by volume of air.
3. In the combined form, it is present as ammonia and all ammonium compounds, in nitric acid and in all nitrates, nitrites and in all living things in the form of proteins.

The chief source of free nitrogen is atmospheric air and nitrogen is usually prepared from it. Air free from dust, water vapour and carbon dioxide is compressed in a compression chamber for liquefaction.

Firstly, the pressure on the air is increased to about 200 atmospheres. It is then released through a spiral into a low-pressure area, where intense cooling of the air takes place.

Ammonia and Ammonium Compounds

By treating excess ammonia with chlorine, ammonium chloride and nitrogen are formed.

In the laboratory, nitrogen is prepared by heating a mixture of ammonium chloride and sodium nitrite and a small quantity of water. If ammonium nitrite is heated by itself it decomposes to produce nitrogen gas. However, this reaction is very fast and may prove to be explosive.

• Color: Nitrogen is a colorless gas.
• Odor: It has no odor.
• Taste: It is a tasteless gas.
• It provides an inter atmosphere.
• Liquid nitrogen is colorless and odorless but resembles with water in appearance.
• Nitrogen exists in two allotropic forms a and b, with a transition temperature of -237° C.
• Density of nitrogen is 1.25 x 10^-3 g.cm^-3 at 20°C
• Melting point of nitrogen is -210 °C
• Boiling point of nitrogen is -195.8 °C

Combination with elements. Nitrogen does not easily combine with other elements under ordinary conditions. A molecule of nitrogen is diatomic. These two atoms have combined by mutually sharing three pairs of electrons.

• Nitrogen form compounds through biological activity, at high or moderate temperature in the presence of catalysts.
• It forms nitric oxide and nitrogen dioxide with oxygen.
• Its reacts withe hydrogen to give ammonia.
• It gives nitrogen sulfide when treated with sulfur.
• At a high very temperatures nitrogen can combine with certain active metals, such as lithium, magnesium and titanium to form metal nitrides.
• It is not a supporter of combustion.
• Energy of first ionization: 1402 kJ.mol ^-1
• Energy of second ionization:  2856 kJ.mol ^-1
• Energy of third ionization: 4577 kJ.mol ^-1
• Electronegativity according to Pauling: 3.0

Nitrogen has 5 electrons in its valence shell. It has a valency of 3 with respect to hydrogen and a valency up to 5 with respect to oxygen. So it can combine with various elements to form many compounds.
The well known compounds of nitrogen are

1. Hydrazine
2. Hydrazoic acid
3. Hydroxylamine
4. Nitrous oxide
5. Nitric oxide
6. Di nitrogen trioxide
7. Nitrogen dioxide

1. This is compound can be regarded as being formed by replacing one H atom of NH₃ molecule by NH₂ group.This was first prepared by Curtius in 1889.
2. Free hydrazine is a colorless liquid, very hygroscopic and soluble in alcohol and water.It is not very stable.
3. On exposure to air, it readily absorbs carbon dioxide and moisture.
4. It dissolves sulfur, arsenic, selenium and phosphorus.Its boiling point is 113.5°C and melting point is 1.4°C.

• It is a hydroxy derivative of NH₃ and was discovered by Lossen in 1865.
• As a rule only the salts of hydroxylamine are prepared because the preparation of free hydroxylamine is difficult and not without hazards under some conditions.
• Its like needle like white substance.
• Melting point is 33°C and boiling point is 58°C at 22 mm pressure.
• It decomposes at steam temperature.
• It is readily soluble in water but not much in alcohol.
• It can be crystallized out from its ethereal solution.
• Its solution in water is a weak base.

• It explodes with halogen and also with permanganate and dichromate.
• Its is very unstable and the solid decomposes slowly above 15°C.

• This oxide is also called as nitrous oxide and is produced when a mixture of nitrogen and oxygen is passed through an electric arc.

• Its is a colorless gas , heavier than air and very sparingly soluble in water.
• Under pressure it changes to a colorless liquid under -151°C.
• The gas is neutral to litmus solution.
• It combines with O₂ to form brown fumes and nitrogen peroxide(NO₂).
• It reacts with burning charcoal, S, P to give oxides.

• The formula of this oxide is N₂O.
• When this oxide is inhaled in small quantities, it produces hysterical laughter and for this reason this oxide is also called as laughing gas.
• It is prepared by heating a mixture of NaNO₃ and (NH₄)₂SO₄.

• Nitrous oxide is a colorless gas having a faint sweetish smell and a sweet taste.
• When inhaled for long, it produces insensibility.
• Large quantities may prove fatal.
• This is soluble in water and the solution has a sweetish taste.
• That is why it is collected over hot water.
• It is heavier than air. It can be easily liquified at 0°C and pressure of 30 atm.
• The liquid boils at -89.5°C.
• The gas is neutral to litmus.

• The formula is N₂O₃.
• This oxide is also called as nitrogen sesquioxide.
• It is also called nitrous anhydride.this means it is the anhydride of HNO₂, since it gives it gives HNO₂ when heated with H₂O.

• Nitrogen trioxide is prepared by the reduction of nitric acid with arsenious oxide.

• It is a red colored gas.
• On condensing , it gives a dark blue liquid.
• It is acidic in nature and reacts with sodium hydroxide to form sodium nitrite.

1. Nitrogen is used in high temperature thermometers where mercury cannot be used.
2. This is because mercury boils at 356.7^oC and hence cannot be used in such thermometers.
3. A volume of nitrogen is enclosed in a vessel and introduced into the region of high temperature.
4. Depending upon the temperature, expansion of the nitrogen volume takes place.
5. Then applying the gas equation, the temperature is calculated