Electronic Configuration and Occurrence of Group 1 and Group 2 Elements

Group 1: general electronic configuration. Every alkali metal atom has the configuration of the preceding noble gas plus one additional electron in the outermost s orbital, written generally as $[\text{noble gas}]\,ns^1$: lithium $[\text{He}]\,2s^1$, sodium $[\text{Ne}]\,3s^1$, potassium $[\text{Ar}]\,4s^1$, rubidium $[\text{Kr}]\,5s^1$, caesium $[\text{Xe}]\,6s^1$, and francium $[\text{Rn}]\,7s^1$. Because this lone outer electron is easily lost to give a stable noble-gas-configured $\text{M}^+$ ion, every alkali metal is univalent and strongly electropositive.

Group 2: general electronic configuration. Every alkaline earth metal atom has the configuration of the preceding noble gas plus two electrons filling the outermost s orbital, $[\text{noble gas}]\,ns^2$: beryllium $[\text{He}]\,2s^2$, magnesium $[\text{Ne}]\,3s^2$, calcium $[\text{Ar}]\,4s^2$, strontium $[\text{Kr}]\,5s^2$, barium $[\text{Xe}]\,6s^2$, and radium $[\text{Rn}]\,7s^2$. Losing both outer electrons gives the stable, noble-gas-configured $\text{M}^{2+}$ ion, so every Group 2 element is characteristically divalent.

Occurrence. Because both families are so reactive, none occurs free; all occur combined, chiefly as chlorides, carbonates, sulfates, nitrates and silicates.

• Lithium occurs mainly in the mineral ores spodumene, $\text{LiAlSi}_2\text{O}_6$, and lepidolite, a complex lithium-aluminium silicate.
• Sodium occurs abundantly as rock salt, $\text{NaCl}$; as Chile saltpetre, $\text{NaNO}_3$; and as borax, $\text{Na}_2\text{B}_4\text{O}_7\!\cdot\!10\text{H}_2\text{O}$.
• Potassium occurs as sylvite, $\text{KCl}$, and carnallite, $\text{KCl}\!\cdot\!\text{MgCl}_2\!\cdot\!6\text{H}_2\text{O}$.
• Beryllium occurs mainly as beryl, $\text{Be}_3\text{Al}_2\text{Si}_6\text{O}_{18}$ (the same mineral, when gem-quality and coloured, gives emerald and aquamarine). …