erbium vs atomic number 68

erbium and atomic number 68 both are nouns.

Word	Noun	Adjective	Verb	Adverb
erbium	Yes	No	No	No
atomic number 68	Yes	No	No	No

As nouns, erbium and atomic number 68 are synonyms defined as:

erbium and atomic number 68: a trivalent metallic element of the rare earth group; occurs with yttrium

Other synonyms of erbium include Er.

erbium (noun)	atomic number 68 (noun)
a trivalent metallic element of the rare earth group; occurs with yttrium	a trivalent metallic element of the rare earth group; occurs with yttrium