Rb vs rubidium

Rb and rubidium both are nouns.

Word	Noun	Adjective	Verb	Adverb
Rb	Yes	No	No	No
rubidium	Yes	No	No	No

As nouns, Rb and rubidium are synonyms defined as:

Rb and rubidium: a soft silvery metallic element of the alkali metal group; burns in air and reacts violently in water; occurs in carnallite and lepidolite and pollucite

Other synonyms of Rb include atomic number 37.

Rb (noun)	rubidium (noun)
a soft silvery metallic element of the alkali metal group; burns in air and reacts violently in water; occurs in carnallite and lepidolite and pollucite	a soft silvery metallic element of the alkali metal group; burns in air and reacts violently in water; occurs in carnallite and lepidolite and pollucite