( ( When ( ( the atoms ) ( are ( relatively ( similar ( in size ) ) ) ) ) ) ( , ( ( the ( atom ( exchange method ) ) ) ( usually ( ( ( happens , ) ( where ( ( some ( of ( ( the atoms ) ( composing ( the ( metallic crystals ) ) ) ) ) ) ( are ( substituted ( with ( atoms ( of ( the ( other constituent ) ) ) ) ) ) ) ) ) ) . ) ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (DT the) (NNS atoms)) (VP (VBP are) (ADJP (RB relatively) (JJ similar) (PP (IN in) (NP (NN size))))))) (, ,) (NP (DT the) (NN atom) (NN exchange) (NN method)) (ADVP (RB usually)) (VP (VBZ happens) (, ,) (SBAR (WHADVP (WRB where)) (S (NP (NP (DT some)) (PP (IN of) (NP (NP (DT the) (NNS atoms)) (VP (VBG composing) (NP (DT the) (JJ metallic) (NNS crystals)))))) (VP (VBP are) (VP (VBN substituted) (PP (IN with) (NP (NP (NNS atoms)) (PP (IN of) (NP (DT the) (JJ other) (NN constituent)))))))))) (. .)))
When the atoms are relatively similar in size, the atom exchange method usually happens, where some of the atoms composing the metallic crystals are substituted with atoms of the other constituent.
(ROOT (S (NP (JJ Metallic) (NNS solids)) (VP (VBP are) (VP (VBN composed) (ADVP (RB entirely)) (PP (IN of) (NP (JJ metallic) (NNS atoms))))) (. .)))