( They ( ( are ( ( ( ( NOT ( chemical bonds ) ) , ) ( but just ) ) ( attractive forces ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBP are) (NP (NP (NNP NOT) (NN chemical) (NNS bonds)) (, ,) (CONJP (CC but) (RB just)) (NP (JJ attractive) (NNS forces)))) (. .)))
They are NOT chemical bonds, but just attractive forces.
(ROOT (S (NP (DT A) (-LRB- -LRB-) (NN n) (-RRB- -RRB-) (NN chemical) (NN bond)) (VP (VBZ is) (NP (NP (DT a) (NN force)) (PP (IN of) (NP (NP (NN attraction)) (PP (IN between) (NP (NNS ions) (CC and) (NNS atoms))))))) (. .)))