( ( ( ( ( ( ( Negatively charged ) electrons ) ( are ( attracted ( to ( ( the ( ( positively charged ) protons ) ) ( in ( the nucleus ) ) ) ) ) ) ) , ) but ) ( ( ( the speed ) ( of ( the electrons ) ) ) ( ( keeps them ) ( in ( ( ( ( their ( energy level ) ) , ) or ) shell ) ) ) ) ) . )
(ROOT (S (S (NP (ADJP (RB Negatively) (VBN charged)) (NNS electrons)) (VP (VBP are) (VP (VBN attracted) (PP (TO to) (NP (NP (DT the) (ADJP (ADVP (RB positively)) (VBN charged)) (NNS protons)) (PP (IN in) (NP (DT the) (NN nucleus)))))))) (, ,) (CC but) (S (NP (NP (DT the) (NN speed)) (PP (IN of) (NP (DT the) (NNS electrons)))) (VP (VBZ keeps) (NP (PRP them)) (PP (IN in) (NP (NP (PRP$ their) (NN energy) (NN level)) (, ,) (CC or) (NP (NN shell)))))) (. .)))
Negatively charged electrons are attracted to the positively charged protons in the nucleus, but the speed of the electrons keeps them in their energy level, or shell.
(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)))))) (. .)))