Why are neither the alkali metals nor the alkaline-earth metals found uncombined in nature?
The alkali and alkaline earth metals are rarely found unreacted because they are so reactive.
All of the IA group elements ( Alkali metals) have only one valance electron.
So losing electrons will make sodium more stable so this is what all the Alkali Metals tend to do. Because of this the electro negativity of the Alkali Metals is the lowest of any group of elements.
The same is basically true of the group II A alkaline earth metals.
The Alkaline earth metals have 2 s electrons