calcium ion vs atomic number 20

calcium ion and atomic number 20 both are nouns.

Word	Noun	Adjective	Verb	Adverb
calcium ion	Yes	No	No	No
atomic number 20	Yes	No	No	No

As nouns, atomic number 20 is a hypernym of calcium ion; that is, atomic number 20 is a word with a broader meaning than calcium ion:

calcium ion: ion of calcium; a factor in the clotting of blood
atomic number 20: a white metallic element that burns with a brilliant light; the fifth most abundant element in the earth's crust; an important component of most plants and animals

Other hypernyms of calcium ion include Ca, calcium, clotting factor, coagulation factor.

calcium ion (noun)	atomic number 20 (noun)
ion of calcium; a factor in the clotting of blood	a white metallic element that burns with a brilliant light; the fifth most abundant element in the earth's crust; an important component of most plants and animals