( ( Valence electrons ) ( ( are ( ( the electrons ) ( that ( are ( on ( ( ( the ( outermost ( energy level ) ) ) ( -LRB- ( shell -RRB- ) ) ) ( of ( the atom ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Valence) (NNS electrons)) (VP (VBP are) (NP (NP (DT the) (NNS electrons)) (SBAR (WHNP (WDT that)) (S (VP (VBP are) (PP (IN on) (NP (NP (NP (DT the) (JJ outermost) (NN energy) (NN level)) (PRN (-LRB- -LRB-) (NP (NN shell)) (-RRB- -RRB-))) (PP (IN of) (NP (DT the) (NN atom)))))))))) (. .)))
Valence electrons are the electrons that are on the outermost energy level (shell) of the atom.
(ROOT (S (NP (NP (NNS Electrons)) (PP (IN in) (NP (NP (DT the) (JJ outer) (NN energy) (NN level)) (PP (IN of) (NP (DT an) (NN atom)))))) (VP (VBP are) (VP (VBN called) (NP (JJ valence) (NNS electrons)))) (. .)))