Nitrogen
. Nitrogen, symbol N, gaseous element that makes up the largest portion of the earth's atmosphere . The atomic number of nitrogen is 7. Nitrogen is in group 15 (or Va) of the periodic table . Nitrogen was isolated by the British physician Daniel Rutherford in 1772 and recognized as an elemental gas by the French chemist Antoine Laurent Lavoisier about 1776. Nitrogen is a colorless, odorless, tasteless, nontoxic gas. It can be condensed into a colorless liquid, which can in turn be compressed into a colorless, crystalline solid. Nitrogen exists in two natural isotopic forms, and four radioactive isotopes have been artificially prepared. Nitrogen melts at -210.01° C (-346.02° F), boils at -195.79° C (-320.42° F), and has a density of 1.251 g/liter at 0° C (32° F) and 1 atmosphere pressure. The atomic weight of nitrogen is 14.007. Nitrogen is obtained from the atmosphere by passing air over heated copper or iron. The oxygen is removed from the air, leaving nitrogen mixed with inert ga