Chemical bonds form when atoms interact to achieve a more stable state. Magnesium chloride (MgCl2) is an inorganic compound formed through a specific type of chemical attraction. The bond holding the magnesium and chlorine atoms together in this compound is classified as an ionic bond.
Defining Ionic and Covalent Bonds
Chemical bonds are primarily categorized into two types: ionic and covalent. This classification is based on the nature of the atoms involved and their relative ability to attract electrons, a property known as electronegativity. Ionic bonds typically form between a metal and a nonmetal, while covalent bonds usually occur between two nonmetal elements.
In an ionic bond, the difference in electronegativity is large (usually greater than 1.7 on the Pauling scale), leading to a complete transfer of electrons. This transfer creates oppositely charged particles called ions. Conversely, a covalent bond involves a smaller electronegativity difference, resulting in the sharing of electrons between atoms. When this sharing is unequal, the bond is called polar covalent.
The Formation of Magnesium Chloride
Magnesium (Mg), an alkaline earth metal in Group 2, possesses two valence electrons. To achieve a stable electron configuration, like the noble gas neon, the magnesium atom readily loses these two valence electrons. When it loses these charges, the magnesium atom becomes a positively charged ion, the Mg2+ cation.
Chlorine (Cl) is a halogen, a nonmetal from Group 17, and has seven valence electrons. For a chlorine atom to reach the stable electron configuration of the noble gas argon, it only needs to gain one electron. Upon gaining this single electron, the chlorine atom forms a negatively charged ion, the Cl- anion. Because the magnesium atom must lose two electrons, and each chlorine atom can only accept one, one magnesium atom must bond with two chlorine atoms to maintain electrical neutrality.
This stoichiometric requirement results in the chemical formula MgCl2. The high electronegativity of chlorine (3.16) compared to magnesium (1.31) creates a difference of 1.85, which ensures the electron transfer mechanism. Once the transfer is complete, the resulting oppositely charged ions are held together by an electrostatic force of attraction, forming the ionic bond.
Properties of Ionic Compounds
The strong electrostatic attraction within MgCl2 gives it physical properties characteristic of all ionic compounds. These bonds require a significant amount of energy to break, leading to high melting and boiling points. Anhydrous magnesium chloride melts at 714°C and boils at 1412°C, demonstrating the stability of the ionic lattice structure.
In its solid state, magnesium chloride forms a crystalline lattice, which is a highly ordered, three-dimensional arrangement of alternating Mg2+ and Cl- ions. This rigid, repeating structure makes the solid material hard but also brittle; any shift in the lattice causes like-charged ions to align, resulting in repulsion and fracture. While the compound does not conduct electricity as a solid because the ions are locked in place, it becomes an excellent electrical conductor when dissolved in water or melted. In these states, the ions are mobile and able to carry an electrical current, further confirming the ionic nature of the compound.