( ( ( The attraction ) ( for ( electrons ( in ( ( the ( outermost shell ) ) ( by ( the nucleus ) ) ) ) ) ) ) ( ( is ( shielded ( by ( electrons ( in ( lower ( energy levels ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN attraction)) (PP (IN for) (NP (NP (NNS electrons)) (PP (IN in) (NP (NP (DT the) (JJ outermost) (NN shell)) (PP (IN by) (NP (DT the) (NN nucleus)))))))) (VP (VBZ is) (VP (VBN shielded) (PP (IN by) (NP (NP (NNS electrons)) (PP (IN in) (NP (JJR lower) (NN energy) (NNS levels))))))) (. .)))
The attraction for electrons in the outermost shell by the nucleus is shielded by electrons in lower energy levels.
(ROOT (S (NP (DT An) (NN electron)) (VP (VBZ moves) (PP (TO to) (NP (NP (DT a) (NN shell)) (ADVP (RB farther) (PP (IN from) (NP (DT the) (NN nucleus)))))) (SBAR (IN after) (S (NP (PRP it)) (VP (VBZ absorbs) (NP (NN energy)))))) (. .)))