( ( The ( atomic mass ) ) ( ( is ( ( the sum ) ( of ( ( the masses ) ( of ( ( ( all ( the protons ) ) and ) neutrons ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (JJ atomic) (NN mass)) (VP (VBZ is) (NP (NP (DT the) (NN sum)) (PP (IN of) (NP (NP (DT the) (NNS masses)) (PP (IN of) (NP (NP (PDT all) (DT the) (NNS protons)) (CC and) (NP (NNS neutrons)))))))) (. .)))
The atomic mass is the sum of the masses of all the protons and neutrons.
(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))))) (. .)))