( They ( ( ( wo n't ) ( ( form ( metal-metal bonds ) ) ( because ( ( their ( valence electrons ) ) ( ( are not ) ( available ( to ( form ( normal ( molecular bonds ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (MD wo) (RB n't) (VP (VB form) (NP (JJ metal-metal) (NNS bonds)) (SBAR (IN because) (S (NP (PRP$ their) (JJ valence) (NNS electrons)) (VP (VBP are) (RB not) (ADJP (JJ available) (S (VP (TO to) (VP (VB form) (NP (JJ normal) (JJ molecular) (NNS bonds))))))))))) (. .)))
They won't form metal-metal bonds because their valence electrons are not available to form normal molecular bonds.
(ROOT (S (NP (DT A) (JJ metallic) (NN bond)) (VP (VBZ is) (NP (NP (DT the) (NN force)) (PP (IN of) (NP (NP (NN attraction)) (PP (IN between) (NP (NP (DT a) (JJ positive) (NN metal) (NN ion)) (CC and) (NP (JJ valence) (NNS electrons)))))))) (. .)))