atomic number 18 vs argon

atomic number 18 and argon both are nouns.

Word	Noun	Adjective	Verb	Adverb
atomic number 18	Yes	No	No	No
argon	Yes	No	No	No

As nouns, atomic number 18 and argon are synonyms defined as:

atomic number 18 and argon: a colorless and odorless inert gas; one of the six inert gases; comprises approximately 1% of the earth's atmosphere

Other synonyms of atomic number 18 include Ar.

atomic number 18 (noun)	argon (noun)
a colorless and odorless inert gas; one of the six inert gases; comprises approximately 1% of the earth's atmosphere	a colorless and odorless inert gas; one of the six inert gases; comprises approximately 1% of the earth's atmosphere