Why density of Ca is smaller than that of Mg?

The density of calcium (Ca) is smaller than that of magnesium (Mg) primarily due to differences in atomic structure and mass. Calcium has a larger atomic radius and a lower Atomic Mass compared to magnesium, resulting in a lower packing efficiency of atoms in its solid form. Additionally, the metallic bonding in magnesium is stronger, leading to a more compact arrangement of atoms, which contributes to its higher density. Overall, the combination of atomic size and bonding characteristics determines the density differences between these two elements.