The 1.0.29 update added group 1 elements' reaction with water, so I think group 2 elements' reaction can also be added to the mod, since that's what happens irl.
The result of the reactions is as follows:

Beryllium reacts with hot steam (>700℃) to produce Beryllium Oxide(BeO).
Magnesium reacts with steam to produce Magnesium Oxide(MgO).
Magnesium also reacts with water to produce magnesium hydroxide(Mg(OH)₂), but the reaction is rather slow and tame, and stops reacting once the surface is coated with Mg(OH)₂.
The rest of the elements will readily react with water with increasing intensity as you go down the periodic table.

The reactions here involve less explosions here. However, for Calcium and heavier elements, when thrown as an whole ingot, they might produce enough H₂ gas and heat, and go boom.

Summary:
Make Calcium, Strontium, Barium, Radium ingots explode when they are thrown into water.
For the element items, form hydroxide and no explosions involved, although one mole of the said element is actually a whole bunch of them. (This is to make things consistent with group 1 elements)
Magnesium: I think it's up to you. Just form Mg(OH)₂ instantly, or give them a few seconds to react.

#138