( ( ( An atom ) ( that ( gains electrons ) ) ) ( ( would ( be ( a ( negative ion ) ) ) ) . ) )
(ROOT (S (NP (NP (DT An) (NN atom)) (SBAR (IN that) (S (NP (NNS gains)) (VP (VBZ electrons))))) (VP (MD would) (VP (VB be) (NP (DT a) (JJ negative) (NN ion)))) (. .)))
An atom that gains electrons would be a negative ion.
(ROOT (S (NP (NP (NNS Atoms)) (SBAR (WHNP (WDT that)) (S (VP (VBP have) (VP (VP (VBN gained) (NP (NNS electrons))) (CC and) (VP (VBN become) (S (VP (ADVP (RB negatively)) (VBN charged))))))))) (VP (VBP are) (VP (VBN called) (NP (JJ negative) (NNS ions)))) (. .)))