( ( As ( ( ( ( ( atomic number ) ( is ( equivalent ( to ( ( the number ) ( of ( protons ( in ( the nucleus ) ) ) ) ) ) ) ) ) , ) and ) ( ( mass number ) ( is ( ( ( ( the ( sum total ) ) ( of ( the protons ) ) ) plus ) ( ( the neutrons ) ( in ( the nucleus ) ) ) ) ) ) ) ) ( , ( ( isotopes ( of ( the ( same element ) ) ) ) ( ( ( differ ( from ( one another ) ) ) ( only ( in ( ( the number ) ( of ( neutrons ( in ( their nuclei ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN As) (S (S (NP (JJ atomic) (NN number)) (VP (VBZ is) (ADJP (JJ equivalent) (PP (TO to) (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NP (NNS protons)) (PP (IN in) (NP (DT the) (NN nucleus)))))))))) (, ,) (CC and) (S (NP (JJ mass) (NN number)) (VP (VBZ is) (NP (NP (NP (DT the) (NN sum) (NN total)) (PP (IN of) (NP (DT the) (NNS protons)))) (CC plus) (NP (NP (DT the) (NNS neutrons)) (PP (IN in) (NP (DT the) (NN nucleus))))))))) (, ,) (NP (NP (NNS isotopes)) (PP (IN of) (NP (DT the) (JJ same) (NN element)))) (VP (VBP differ) (PP (IN from) (NP (CD one) (DT another))) (PP (RB only) (IN in) (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NP (NNS neutrons)) (PP (IN in) (NP (PRP$ their) (NNS nuclei)))))))) (. .)))
As atomic number is equivalent to the number of protons in the nucleus, and mass number is the sum total of the protons plus the neutrons in the nucleus, isotopes of the same element differ from one another only in the number of neutrons in their nuclei.
(ROOT (S (S (S (VP (VBG Adding) (NP (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NNS protons)))) (CC plus) (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NP (NNS neutrons)) (PP (IN in) (NP (DT an) (NN atom))))))))) (VP (VBZ decides) (NP (PRP$ its) (JJ approximate) (NN mass)))) (: ;) (S (NP (JJ atomic) (NN number)) (VP (VBZ is) (NP (NP (DT another) (NN word)) (PP (IN for) (NP (DT this) (NN value)))))) (. .)))