Nitrogen is a chemical element with an atomic number of 7 (it has seven protons in its nucleus). Molecular nitrogen (N2) is a very common chemical compound in which two nitrogen atoms are tightly bound together. Molecular nitrogen is a colorless, odorless, tasteless, and inert gas at normal temperatures and pressures.
About 78% of Earth's atmosphere is nitrogen. The strong triple-bond between the atoms in molecular nitrogen makes this compound difficult to break apart, and thus nearly inert. However, when nitrogen bonds do break, the resulting products are often highly reactive.
Nitrogen atoms are part of several types of pollutants. High temperature combustion in the presence of nitrogen gas, such as in automobile engines, can generate nitric oxide (NO) and nitrogen dioxide (NO2). Both gases are poisonous on their own, while they also play a role in the production of peroxyacetyl nitrate (PAN), a major component of smog, and nitric acid, which is part of acid rain.
Nitrogen gas can be used to manufacture ammonia (NH3), which is used extensively to produce chemical fertilizers.
Nitrogen is one of the most important elements in the chemistry of living creatures. For example, nitrogen is part of amino acids, the building blocks of proteins. The Nitrogen Cycle traces the path of nitrogen, in many different chemical forms, through the environment and living organisms. Certain microbes can take gaseous nitrogen from the air and convert it to ammonia, making it available to plants and other organisms in a process called "nitrogen fixation".