The chemical formula of nitrogen molecule is N2. Nitrogen is usually a colorless and odorless gas, and its density is usually smaller than that of air. In air, the volume fraction of nitrogen is 78%, which is the main component of air. At standard atmospheric pressure, when cooled to-195 and 8 degrees Celsius, it becomes a colorless liquid, and when cooled to -209 and 8 degrees Celsius, liquid nitrogen becomes a snow-like solid.

Chemical properties of N2:

1. Because the triple bond energy in nitrogen molecule is very large, it is not easy to be destroyed, so its chemical properties are very stable. Only under the conditions of high temperature and high pressure and the presence of catalyst can nitrogen react with hydrogen to generate ammonia.

2. In the case of discharge, nitrogen and oxygen combine to form nitric oxide. Nitric oxide quickly combines with oxygen to form nitrogen dioxide, which dissolves in water to form nitric acid.

Use of N2:

(1) Nitrogen is an important raw material for producing nitric acid and nitrogen fertilizer.

(2) Nitrogen is inert, so it can be used as a common protective gas for welding metal, which can prevent metal oxidation.

(3) Filling the bulb with nitrogen can prolong the service life.

(4) Filling nitrogen into edible packaging can prevent decay.

(5) The operation can be performed under the condition of liquid nitrogen freezing anesthesia.

(6) Superconducting materials show superconductivity in the low temperature environment of liquid nitrogen.