( ( When ( ( atoms ( of ( a metal ) ) ) ( combine ( with ( atoms ( of ( a nonmetal ) ) ) ) ) ) ) ( , ( they ( ( produce ( an ( ionic compound ) ) ) . ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NP (NNS atoms)) (PP (IN of) (NP (DT a) (NN metal)))) (VP (VBP combine) (PP (IN with) (NP (NP (NNS atoms)) (PP (IN of) (NP (DT a) (NN nonmetal)))))))) (, ,) (NP (PRP they)) (VP (VBP produce) (NP (DT an) (JJ ionic) (NN compound))) (. .)))
When atoms of a metal combine with atoms of a nonmetal, they produce an ionic compound.
(ROOT (S (NP (NP (JJ Ionic) (NNS bonds)) (PP (IN between) (NP (CD two) (NNS atoms)))) (VP (VBP require) (NP (NP (CD one) (NN metal)) (CC and) (NP (CD one) (NN nonmetal)))) (. .)))