Magnesium is an alkaline earth metal, possessing a strong tendency to give up electrons. Chlorine, a halogen in Group 17, has a powerful urge to acquire electrons to achieve stability. When these two elements are brought together, their opposing chemical drives result in a vigorous, rapid combination. This strong chemical reaction yields a single, stable substance.
The Compound Formed: Magnesium Chloride
The reaction between magnesium metal (\(\text{Mg}\)) and chlorine gas (\(\text{Cl}_2\)) creates magnesium chloride (\(\text{MgCl}_2\)). This chemical event is classified as a synthesis or combination reaction. The balanced chemical equation shows the reactants combining in a one-to-one molar ratio: \(\text{Mg} + \text{Cl}_2 \rightarrow \text{MgCl}_2\). This formation is a highly exothermic process, releasing a significant amount of energy. The product, magnesium chloride, is a salt that takes the form of a white crystalline solid at room temperature.
Explaining the Ionic Bond Formation
The formation of magnesium chloride is an excellent example of an ionic bond, which involves the complete transfer of electrons between atoms. Magnesium, being in Group 2, has two valence electrons. To achieve a stable electron configuration, the magnesium atom readily gives up both electrons, resulting in the formation of a positively charged \(\text{Mg}^{2+}\) cation.
Meanwhile, chlorine is a nonmetal with seven valence electrons, requiring one additional electron to complete its stable outer shell. When a chlorine atom gains this single electron, it transforms into a negatively charged \(\text{Cl}^{-}\) anion.
Since the magnesium atom donates two electrons, two chlorine atoms are needed to accept one electron each to maintain electrical neutrality. The \(\text{Mg}^{2+}\) cation and the two \(\text{Cl}^{-}\) anions are held together by a strong electrostatic attraction. This force is the ionic bond, resulting in the stable chemical formula \(\text{MgCl}_2\). The final compound exists as a crystal lattice, a three-dimensional arrangement where each magnesium ion is surrounded by chloride ions and vice versa.
Common Uses and Properties of Magnesium Chloride
Magnesium chloride is a highly soluble salt, meaning it dissolves readily in water, where it dissociates back into its constituent \(\text{Mg}^{2+}\) and \(\text{Cl}^{-}\) ions. The pure, anhydrous form has a high melting point of 714°C, but it is often encountered as a hydrated salt, such as the hexahydrate (\(\text{MgCl}_2 \cdot 6\text{H}_2\text{O}\)), which melts at a much lower temperature.
Magnesium chloride is used in winter road maintenance as a de-icing agent. It is effective at lower temperatures than traditional rock salt (sodium chloride), making it a preferred choice in colder climates. Its ability to absorb moisture from the air, known as hygroscopicity, also makes it useful for dust control on unpaved roads and construction sites.
In the food industry, magnesium chloride, often referred to as nigari, serves as a coagulant. This is important in the production of tofu, where it helps separate the curds from the soy milk. It is also used as a dietary supplement to treat or prevent magnesium deficiency, favored for its high solubility and good absorption rate.