Nitrogen (N) is the element with atomic number 7, symbol N. Its most common isotope has mass number 14, with 15 being another stable isotope. It is the seventh most common element in the universe and is formed by fusion of carbon and hydrogen in supernovae. It is very stable in its molecular form, N2, with a triple bond and typically it is easer to convert another compound to N2 than the reverse. It is volatile in its atomic form. Nitrogen molecules (N2) are thought to be broken (e.g., "fixed", converted to ammonium, NH4+) through UV emission, lightening, and energetic particles.
Nitrogen is transparent in infrared and visible light radiation, but absorbs some ultraviolet. The spectral lines of atomic nitrogen are grouped into NI (neutral nitrogen), NII (singly ionized), NIII (doubly ionized), etc.