atomic number 3 vs lithium

atomic number 3 and lithium both are nouns.

Word	Noun	Adjective	Verb	Adverb
atomic number 3	Yes	No	No	No
lithium	Yes	No	No	No

As nouns, atomic number 3 and lithium are synonyms defined as:

atomic number 3 and lithium: a soft silver-white univalent element of the alkali metal group; the lightest metal known; occurs in several minerals

Other synonyms of atomic number 3 include Li.

atomic number 3 (noun)	lithium (noun)
a soft silver-white univalent element of the alkali metal group; the lightest metal known; occurs in several minerals	a soft silver-white univalent element of the alkali metal group; the lightest metal known; occurs in several minerals