( ( An ( oxygen atom ) ) ( ( ( gains ( two electrons ) ) ( to ( form ( the ( oxide ion ) ) ) ) ) . ) )
(ROOT (S (NP (DT An) (NN oxygen) (NN atom)) (VP (VBZ gains) (NP (CD two) (NNS electrons)) (S (VP (TO to) (VP (VB form) (NP (DT the) (NN oxide) (NN ion)))))) (. .)))
An oxygen atom gains two electrons to form the oxide ion .
(ROOT (S (NP (DT Some) (NNS atoms)) (VP (VBP are) (ADJP (ADJP (RBR more) (JJ stable)) (SBAR (WHADVP (WRB when)) (S (NP (PRP they)) (VP (VB gain) (CC or) (VB lose) (NP (DT an) (NN electron) (CC and) (NN form) (NNS ions))))))) (. .)))