alkaline earth metals

Meaning: The alkaline earth metals are beryllium, magnesium, calcium, strontium, barium and radium. Each has two valence electrons (ns²). Losing both gives an M²⁺ ion with a noble-gas configuration, so this is the charge they usually carry in compounds. Going down the group, atomic radius increases, first ionization energy and electronegativity decrease, and reactivity with water increases. They are less reactive than the Group 1 metals beside them, because their nuclear charge is higher and their first ionization energy is greater. Beryllium is the exception. It bonds largely covalently, and its oxide is amphoteric. The oxides and hydroxides of the other members are basic, which gives the group its name.

On the MCAT: Expect periodic-trend rankings, such as ordering Mg, Ca and Ba by radius, ionization energy or reactivity. Successive ionization energy data are common. The second ionization energy is only modestly larger than the first, but the third is far larger because it removes a core electron. That jump shows the element is in Group 2. Solubility questions also appear. Group 2 sulfates generally become less soluble down the group, so BaSO₄ is very insoluble. Hydroxides generally become more soluble down the group.

Common confusion: Students mix up Group 1 and Group 2. Alkali metals form +1 ions, and alkaline earth metals form +2 ions. Also, "alkaline" describes their basic oxides and hydroxides, not a lack of reactivity.