europium vs atomic number 63

europium and atomic number 63 both are nouns.

Word	Noun	Adjective	Verb	Adverb
europium	Yes	No	No	No
atomic number 63	Yes	No	No	No

As nouns, europium and atomic number 63 are synonyms defined as:

europium and atomic number 63: a bivalent and trivalent metallic element of the rare earth group

Other synonyms of europium include Eu.

europium (noun)	atomic number 63 (noun)
a bivalent and trivalent metallic element of the rare earth group	a bivalent and trivalent metallic element of the rare earth group