( ( Isotopic ( ( mass and ) ( atomic mass ) ) ) . )
(ROOT (NP (NP (NNP Isotopic)) (NP (NP (NN mass)) (CC and) (NP (JJ atomic) (NN mass))) (. .)))
Isotopic mass and atomic mass.
(ROOT (S (NP (NP (DT The) (NN sum)) (PP (IN of) (NP (NP (DT the) (NNS masses)) (PP (IN of) (NP (NP (DT the) (NNS atoms)) (PP (IN in) (NP (DT the) (NN formula)))))))) (VP (VBZ is) (VP (VBN referred) (PP (TO to) (NP (RB as) (JJ molecular) (NN mass))))) (. .)))