( ( ( The ( outer electrons ) ) ( that ( participate ( in ( chemical bonding ) ) ) ) ) ( ( are ( called ( valence electrons ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (JJ outer) (NNS electrons)) (SBAR (WHNP (WDT that)) (S (VP (VBP participate) (PP (IN in) (NP (NN chemical) (NN bonding))))))) (VP (VBP are) (VP (VBN called) (NP (JJ valence) (NNS electrons)))) (. .)))
The outer electrons that participate in chemical bonding are called valence electrons.
(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)))) (. .)))