Question

The solubility of carbonates decrease down the magnesium group (alkaline earth metals) due to a decrease in:

Answer 1

You mean solubility in water. As you go down the periodic table, the valence electrons become more dense; that is, they have more layers, like an onion. The valence electrons, the outermost electrons, are therefore shielded, referred to as ‘Z’ by the inner layers of electrons from the nucleus.

The nucleus therefore has less of a grip on the outermost electrons because of this Z shielding effect.

As a result, we often find the outer electrons wandering off, but the nucleus remaining intact, but in a different ‘oxidation state’, referring to the fact that it has less electrons because they wandered off with the water.