How do alkaline-earth metals differ from alkali metals?

Alkaline-earth metals and alkali metals differ primarily in their electronic structure, reactivity, and physical properties, as outlined below:

Electronic Structure and Oxidation States

• Alkali Metals: Each atom has a single valence electron in its outermost shell, leading them to form singly charged positive ions (+1 oxidation state) when reacting with nonmetals.1
• Alkaline-Earth Metals: These atoms possess a pair of s electrons in their outermost orbital. Their chemistry is dominated by the formation of doubly charged M${}^{2+}$ ions (+2 oxidation state).2

Ionization Energy and Electronegativity

• Ionization Energy: Because alkali metals have only one weakly bound valence electron, they are more easily ionized than alkaline-earth metals. Consequently, alkali metals have lower ionization energies compared to the alkaline-earth group.1
• Electronegativity: Alkali metals are the least electronegative elements (ranging from 0.7 to 1.0), whereas alkaline-earth metals have slightly higher electronegativity values (ranging from about 0.9 to 1.5).1

Physical Properties

• Melting and Boiling Points: Alkaline-earth metals generally have higher melting and boiling points than the corresponding alkali metals.2
• Density and Structure: Alkali metals have a looser crystallographic arrangement and lower densities than other metallic crystals; some, such as lithium, sodium, and potassium, are less dense than water. Alkaline-earth metals are highly metallic and exhibit higher densities.12