Question

Why are alkaline earth metals relatively harder than alkali metals?

Answer 1

ou need to look at metal structures to understand this. Basically the metals structure is made of metals ions in a mobile sea of their valency electrons. [It is because of these mobile valency electrons that all metals conduct electricity] 

With the alkali metals there is an ion with one positive charge eg Na+ and one delocalised electron whereas with the alkaline earths there is an ion with two positive charges and two delocalised electrons. Clearly there is greater attraction between the 2+ ions and two electrons than the 1+ ion for the alkali metals, and this makes the group II metals harder.