( ( ( ( ( The simplest ) , ) ( the ( metal-to-metal bond ) ) ) , ) ( ( is ( ( thought ( of ( as ( ( a sea ) ( of ( loose electrons ) ) ) ) ) ) ( ( holding ( metal atoms ) ) together ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (JJS simplest)) (, ,) (NP (DT the) (JJ metal-to-metal) (NN bond)) (, ,)) (VP (VBZ is) (VP (VBN thought) (PP (IN of) (IN as) (NP (NP (DT a) (NN sea)) (PP (IN of) (NP (JJ loose) (NNS electrons))))) (S (VP (VBG holding) (NP (NN metal) (NNS atoms)) (ADVP (RB together)))))) (. .)))
The simplest, the metal-to-metal bond, is thought of as a sea of loose electrons holding metal atoms together.
(ROOT (S (NP (JJ Metallic) (NNS bonds)) (VP (VBP hold) (PRT (RP together)) (NP (NP (JJ positive) (NN metal) (NNS ions)) (CC and) (NP (PRP$ their) (JJ valence) (NNS electrons)))) (. .)))