# What is the difference between two hydrogen atoms, and one hydrogen molecule?

${H}_{2} \rightarrow 2 H \cdot$
The standard state of elemental hydrogen is as the dihydrogen molecule, ${H}_{2}$. We could add energy to the LHS of the equation above and produce two hydrogen atoms as shown. The $H \cdot$ radical is a highly reactive species - of course it could react with another $H \cdot$ species (to form what), but it could also react with $C - H$ or $X - X$ bonds to form $C \cdot$ and $X \cdot$ radicals that continue the chain of reactivity.