( ( The ( octet rule ) ) ( ( states ( that ( atoms ( completely ( fill ( outer ( energy levels ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN octet) (NN rule)) (VP (VBZ states) (SBAR (IN that) (S (NP (NNS atoms)) (ADVP (RB completely)) (VP (VB fill) (NP (JJ outer) (NN energy) (NNS levels)))))) (. .)))
The octet rule states that atoms completely fill outer energy levels.
(ROOT (S (NP (DT The) (NN octet) (NN rule)) (VP (VP (VBZ is) (NP (NP (DT a) (NN result)) (PP (IN of) (NP (NP (NNS trends)) (PP (IN in) (NP (NNS energies))))))) (CC and) (VP (VBZ is) (ADJP (JJ useful) (PP (IN in) (S (VP (VBG explaining) (SBAR (WHADVP (WRB why)) (S (NP (NNS atoms)) (VP (VBP form) (NP (DT the) (NNS ions)) (SBAR (IN that) (S (NP (PRP they)) (VP (VBP do))))))))))))) (. .)))