Occurrence and Extraction — Core Principles

Core Principles

Alkaline earth metals (Group 2: Be, Mg, Ca, Sr, Ba, Ra) are highly reactive due to their $ns^2$ electron configuration, readily forming $M^{2+}$ ions. Consequently, they are never found as free metals in nature, always occurring in combined forms within minerals and ores.

Key ores include Beryl for Beryllium, Magnesite, Dolomite, and Carnallite for Magnesium, Limestone and Gypsum for Calcium, Strontianite and Celestite for Strontium, and Barytes and Witherite for Barium.

Radium is found in Pitchblende. The primary extraction method for these electropositive metals is the electrolysis of their molten chlorides, as chemical reduction with carbon is generally ineffective, and aqueous electrolysis would reduce water instead of the metal ions.

Dow's process is a notable industrial method for extracting magnesium from seawater via electrolysis of molten $MgCl_2$. Thermal reduction with more reactive metals or ferrosilicon is also used for some elements like magnesium, strontium, and barium under specific conditions.

Important Differences

vs Extraction of Alkali Metals (Group 1)

Aspect	This Topic	Extraction of Alkali Metals (Group 1)
Reactivity	Alkaline Earth Metals (Group 2): Highly reactive, but generally less reactive than alkali metals.	Alkali Metals (Group 1): Extremely reactive, highest electropositivity in their respective periods.
Valency/Ion Formation	Alkaline Earth Metals (Group 2): Form dipositive ions ($M^{2+}$) by losing two electrons.	Alkali Metals (Group 1): Form monopositive ions ($M^{+}$) by losing one electron.
Primary Extraction Method	Alkaline Earth Metals (Group 2): Electrolysis of molten chlorides (e.g., $MgCl_2$, $CaCl_2$). Thermal reduction (e.g., Pidgeon process for Mg) also used.	Alkali Metals (Group 1): Exclusively by electrolysis of molten chlorides (e.g., Down's process for Na). No practical thermal reduction due to extreme reactivity.
Electrolysis Conditions	Alkaline Earth Metals (Group 2): Molten chlorides, often with fluxing agents (e.g., $CaF_2$ for $CaCl_2$) to lower melting point.	Alkali Metals (Group 1): Molten chlorides, often with $CaCl_2$ to lower melting point (e.g., for $NaCl$).
Ease of Reduction	Alkaline Earth Metals (Group 2): Require significant energy for reduction; slightly easier than alkali metals due to higher charge density and smaller size of $M^{2+}$ ions (relative to $M^+$).	Alkali Metals (Group 1): Extremely difficult to reduce their ions due to very high electropositivity and very negative standard reduction potentials.

While both alkali and alkaline earth metals are highly reactive and primarily extracted by the electrolysis of their molten chlorides, there are subtle yet important differences. Alkali metals are even more reactive, forming monopositive ions, and their extraction is almost exclusively by electrolysis. Alkaline earth metals, forming dipositive ions, are also extracted by electrolysis but some, like magnesium, can also be obtained via thermal reduction methods under specific conditions. The energy requirements and specific cell designs might also differ slightly due to their distinct ionic charges and sizes, influencing melting points and conductivities of their molten salts.