( ( In chemistry ) ( , ( ( a ( pure element ) ) ( ( means ( ( ( ( ( a substance ) ( ( whose ( atoms ( all ( -LRB- ( ( or ( ( in ( practice almost ) ) all ) ) -RRB- ) ) ) ) ) ( have ( the ( same ( atomic number ) ) ) ) ) ) , ) or ) ( number ( of protons ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN In) (NP (NN chemistry))) (, ,) (NP (DT a) (JJ pure) (NN element)) (VP (VBZ means) (NP (NP (NP (DT a) (NN substance)) (SBAR (WHNP (WP$ whose) (NP (NP (NNS atoms)) (ADJP (DT all) (PRN (-LRB- -LRB-) (CC or) (FRAG (PP (IN in) (NP (NN practice) (RB almost))) (NP (DT all))) (-RRB- -RRB-))))) (S (VP (VBP have) (NP (DT the) (JJ same) (JJ atomic) (NN number)))))) (, ,) (CC or) (NP (NP (NN number)) (PP (IN of) (NP (NNS protons)))))) (. .)))
In chemistry, a pure element means a substance whose atoms all (or in practice almost all) have the same atomic number, or number of protons.
(ROOT (S (NP (NNS Elements)) (VP (VBP are) (NP (NP (JJ pure) (NNS substances)) (SBAR (WHNP (WDT that)) (S (VP (VBP make) (ADVP (RB up) (DT all) (NN matter))))))) (. .)))