mercury vs atomic number 80

mercury and atomic number 80 both are nouns.

Word	Noun	Adjective	Verb	Adverb
mercury	Yes	No	No	No
atomic number 80	Yes	No	No	No

As nouns, mercury and atomic number 80 are synonyms defined as:

mercury and atomic number 80: a heavy silvery toxic univalent and bivalent metallic element; the only metal that is liquid at ordinary temperatures

Other synonyms of mercury include Hg, hydrargyrum, quicksilver.

mercury (noun)	atomic number 80 (noun)
temperature measured by a mercury thermometer	a heavy silvery toxic univalent and bivalent metallic element; the only metal that is liquid at ordinary temperatures
a heavy silvery toxic univalent and bivalent metallic element; the only metal that is liquid at ordinary temperatures