( ( If ( there ( is ( ( no number ) ( written ( after ( an element ) ) ) ) ) ) ) ( , ( it ( ( means ( there ( is ( ( only ( one atom ) ) ( of ( that ( element present ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN If) (S (NP (EX there)) (VP (VBZ is) (NP (NP (DT no) (NN number)) (VP (VBN written) (PP (IN after) (NP (DT an) (NN element)))))))) (, ,) (NP (PRP it)) (VP (VBZ means) (SBAR (S (NP (EX there)) (VP (VBZ is) (NP (NP (RB only) (CD one) (NN atom)) (PP (IN of) (NP (DT that) (NN element) (NN present)))))))) (. .)))
If there is no number written after an element, it means there is only one atom of that element present.
(ROOT (S (NP (PRP You)) (VP (VBP call) (NP (NP (NNS elements)) (SBAR (WHNP (WDT that)) (S (VP (VBP contain) (NP (NP (JJ only) (NNS atoms)) (PP (IN of) (NP (NP (CD one) (NN type)) (PP (IN of) (NP (NN element) (NN native) (NNS elements))))))))))) (. .)))