allotrope vs chemical element

allotrope and chemical element both are nouns.

Word	Noun	Adjective	Verb	Adverb
allotrope	Yes	No	No	No
chemical element	Yes	No	No	No

As nouns, chemical element is a hypernym of allotrope; that is, chemical element is a word with a broader meaning than allotrope:

allotrope: a structurally different form of an element
chemical element: any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter

Other hypernyms of allotrope include element.

allotrope (noun)	chemical element (noun)
a structurally different form of an element	any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter