( ( ( ( The ( atomic weight ) ) ( -LRB- ( or ( ( atomic mass ) -RRB- ) ) ) ) ( of ( an atom ) ) ) ( ( is ( ( the ( combined number ) ) ( of ( its ( ( protons and ) neutrons ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NP (DT The) (JJ atomic) (NN weight)) (PRN (-LRB- -LRB-) (CC or) (ADJP (JJ atomic) (RB mass)) (-RRB- -RRB-))) (PP (IN of) (NP (DT an) (NN atom)))) (VP (VBZ is) (NP (NP (DT the) (VBN combined) (NN number)) (PP (IN of) (NP (PRP$ its) (NNS protons) (CC and) (NNS neutrons))))) (. .)))
The atomic weight (or atomic mass) of an atom is the combined number of its protons and neutrons.
(ROOT (S (S (VP (TO To) (VP (VB determine) (NP (NP (DT the) (JJ atomic) (NN weight)) (PP (IN of) (NP (DT an) (NN element))))))) (, ,) (NP (PRP you)) (VP (MD should) (VP (VB add) (PRT (RP up)) (NP (NNS protons) (CC and) (NNS neutrons)))) (. .)))