The alkali metals (Group 1) and alkaline earth metals (Group 2) represent the first two groups of the periodic table, located on the far left side. Both groups are chemically active metals, sharing many characteristics that stem from their placement and structure. These two families exhibit similar metallic properties, reflecting a common underlying atomic structure. They both readily participate in chemical reactions, which explains why they are rarely found in their pure, uncombined form in nature.
Placement in the S Block
The most fundamental commonality between these two groups lies in their electron configuration, which places them squarely within the s-block of the periodic table. This means that the valence electrons in the atoms of both groups reside exclusively in an \(s\) atomic orbital. Alkali metals have a single electron in their outermost shell, represented by the general configuration \(ns^1\). Alkaline earth metals follow this trend but possess two valence electrons, fitting the configuration \(ns^2\). The presence of only one or two valence electrons makes both groups highly electropositive, meaning they have a strong tendency to lose these outer electrons. Losing these electrons allows the atoms to achieve a stable, noble gas configuration, which dictates how they interact with other elements.
Shared Physical Properties
Beyond their electronic architecture, alkali metals and alkaline earth metals exhibit several similar, easily observable physical characteristics. Both groups are known for their bright, silvery-white appearance, or metallic luster, when freshly cut or polished. This shiny surface tarnishes quickly upon exposure to air due to rapid oxidation. A defining shared trait is their relatively low density and soft nature. While alkali metals are notably soft, alkaline earth metals are typically harder but still considered soft metals overall. Furthermore, the free-moving valence electrons shared across the metallic lattice in both groups facilitate excellent electrical and thermal conductivity.
Common High Chemical Reactivity
The low number of valence electrons in both groups results in low ionization energies, which is the energy required to remove an electron from a gaseous atom. This low energy barrier means that both alkali and alkaline earth metals are among the most reactive elements on the periodic table, readily giving up their valence electrons to form positive ions. This shared propensity to lose electrons dictates that both groups form ionic compounds almost exclusively when reacting with nonmetals; alkali metals lose one electron to form a monovalent cation with a \(+1\) charge, while alkaline earth metals lose two electrons to form a divalent cation with a \(+2\) charge. This common action of electron loss allows both to react vigorously with elements like the halogens (Group 17) and oxygen, and nearly all elements in both groups react strongly with water to produce hydrogen gas and a metal hydroxide, which is a strongly basic, or alkaline, solution. Their tendency to achieve a stable noble gas configuration by readily surrendering electrons makes them strong reducing agents in chemical reactions, meaning neither group is ever found in its elemental form in nature; instead, they are found combined in various salts and minerals.