( ( Valence electrons ) ( ( are ( ( outer electrons ) ( of ( ( an atom ) ( which ( are ( involved ( in ( chemical bonding ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Valence) (NNS electrons)) (VP (VBP are) (NP (NP (JJ outer) (NNS electrons)) (PP (IN of) (NP (NP (DT an) (NN atom)) (SBAR (WHNP (WDT which)) (S (VP (VBP are) (VP (VBN involved) (PP (IN in) (NP (NN chemical) (NN bonding))))))))))) (. .)))
Valence electrons are outer electrons of an atom which are involved in chemical bonding.
(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)))) (. .)))