alkaline earth vs alkaline-earth metal

alkaline earth and alkaline-earth metal both are nouns.

Word	Noun	Adjective	Verb	Adverb
alkaline earth	Yes	No	No	No
alkaline-earth metal	Yes	No	No	No

As nouns, alkaline earth and alkaline-earth metal are synonyms defined as:

alkaline earth and alkaline-earth metal: any of the bivalent metals of group II of the periodic table (calcium or strontium or barium or magnesium or beryllium)

alkaline earth (noun)	alkaline-earth metal (noun)
any of the bivalent metals of group II of the periodic table (calcium or strontium or barium or magnesium or beryllium)	any of the bivalent metals of group II of the periodic table (calcium or strontium or barium or magnesium or beryllium)