= Dinitrogen
{title2=$\mathrm{N_2}$}
<Dinitrogen> is the diatomic <molecule> $\mathrm{N_2}$, consisting of two <nitrogen> <atoms> joined by a strong <triple bond>. It is the principal molecular form of <nitrogen> in Earth's atmosphere. A nitrogen atom incorporated in a <protein> belongs to the same <chemical element>, but is not a dinitrogen molecule.<Chemistry 2e by Paul Flowers and others>[§18.7, atmospheric N2 and its nitrogen–nitrogen triple bond]{ref}
The reaction
$$
\mathrm{N_2+3H_2\longrightarrow 2NH_3}
$$
illustrates the bookkeeping: one dinitrogen molecule supplies the two nitrogen atoms in two <Ammonia> molecules. Breaking and replacing its strong bond requires suitable reaction pathways and conditions. Its abundance therefore does not mean that <organisms> can automatically use it as a source of chemically available <nitrogen>.<Chemistry 2e by Paul Flowers and others>[§18.7, low reactivity, ammonia synthesis and biological nitrogen fixation]{ref}
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