( ( When ( ( the atoms ) ( are ( ( brought together ) ( to ( form ( a solid ) ) ) ) ) ) ) ( , ( ( ( ( ( ( ( these ( discrete ( energy levels ) ) ) become ) ( perturbed ( through ( quantum ( mechanical effects ) ) ) ) ) , ) and ) ( ( ( the ( many electrons ) ) ( in ( ( the collection ) ( of ( individual atoms ) ) ) ) ) ( occupy ( ( a band ) ( of ( levels ( in ( ( the solid ) ( called ( the ( valence band ) ) ) ) ) ) ) ) ) ) ) . ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (DT the) (NNS atoms)) (VP (VBP are) (VP (VBN brought) (ADVP (RB together)) (S (VP (TO to) (VP (VB form) (NP (DT a) (JJ solid))))))))) (, ,) (S (NP (NP (DT these) (JJ discrete) (NN energy) (NNS levels)) (VP (VBN become))) (VP (VBD perturbed) (PP (IN through) (NP (JJ quantum) (JJ mechanical) (NNS effects))))) (, ,) (CC and) (S (NP (NP (DT the) (JJ many) (NNS electrons)) (PP (IN in) (NP (NP (DT the) (NN collection)) (PP (IN of) (NP (JJ individual) (NNS atoms)))))) (VP (VB occupy) (NP (NP (DT a) (NN band)) (PP (IN of) (NP (NP (NNS levels)) (PP (IN in) (NP (NP (DT the) (JJ solid)) (VP (VBN called) (NP (DT the) (JJ valence) (NN band)))))))))) (. .)))
When the atoms are brought together to form a solid, these discrete energy levels become perturbed through quantum mechanical effects, and the many electrons in the collection of individual atoms occupy a band of levels in the solid called the valence band .
(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)))) (. .)))