Final answer:
The reactivity of group 2 alkaline earth metals increases from magnesium to barium due to decreasing ionization energy and increasing atomic size down the group. This trend is consistent among group 2 elements, although they are less reactive than group 1 alkali metals because they need to lose two electrons to react.
Step-by-step explanation:
The student has asked about the trend in reactivity observed in group 2 elements, which are known as alkaline earth metals (beryllium, magnesium, calcium, strontium, barium, and radium). The reactivity of these group 2 metals indeed increases as you move down the group. This is largely attributable to decreasing ionization energy and an increase in atomic size down the group.
As the atomic radius increases, the outer electrons are farther from the nucleus, making it easier for these electrons to be lost, thus increasing the metal's reactivity. In addition, the nuclear charge increases from group 1 to group 2 metals, but because of the larger size of the atomic radius in group 2, the net effect is a reduction in ionization energy as you move down the group. This contributes to an increase in reactivity of group 2 metals from Mg to Ba. These elements are very reactive, but still less reactive than their group 1 counterparts since they need to remove two valence electrons to form compounds with a +2 oxidation state in reactions. However, beryllium and magnesium are exceptions in that they do not react with water at room temperature as the heavier group 2 elements do.