( ( Atomic hydrogen ) ( ( has ( ( only ( a ( single electron ) ) ) ( in ( its ( one orbital ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Atomic) (NN hydrogen)) (VP (VBZ has) (NP (NP (RB only) (DT a) (JJ single) (NN electron)) (PP (IN in) (NP (PRP$ its) (CD one) (NN orbital))))) (. .)))
Atomic hydrogen has only a single electron in its one orbital.
(ROOT (S (NP (EX There)) (VP (VBP are) (NP (NP (CD one) (NNS electrons)) (PP (IN in) (NP (DT the) (NN hydrogen) (NN atom))))) (. .)))