Describe the type of bonding that exists in MgCl2, PCl3, and Ca. Give two properties of each substance and relate this property to the type of bonding.

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Q) Describe the type of bonding that exists in the following substances: Magnesium Chloride ($\text{MgCl}_2$), Phosphorus trichloride ($\text{PCl}_3$), and Calcium (Ca). Give two properties of each substance and relate this property to the type of bonding in this substance.

• Substance: Magnesium Chloride ($\text{MgCl}_2$)

  • Type of Bonding: Ionic Bond
  • Bonding Description: Magnesium ($\text{Mg}$), a metal, transfers its two valence electrons to two chlorine ($\text{Cl}$) atoms, which are non-metals. This forms a positively charged magnesium ion ($\text{Mg}^{2+}$) and two negatively charged chloride ions ($\text{Cl}^-$). These oppositely charged ions are then held together by strong electrostatic forces of attraction, forming a crystal lattice.
  • Property 1: $\text{MgCl}_2$ has a high melting point ($714^\circ\text{C}$).
  • Relation to Bonding: The strong electrostatic forces of attraction between the $\text{Mg}^{2+}$ and $\text{Cl}^-$ ions in the crystal lattice require a large amount of thermal energy to overcome, leading to a high melting point.
  • Property 2: $\text{MgCl}_2$ conducts electricity when molten or dissolved in water.
  • Relation to Bonding: In the molten or aqueous state, the ions ($\text{Mg}^{2+}$ and $\text{Cl}^-$) are free to move and act as charge carriers, allowing the substance to conduct electricity. In the solid state, the ions are fixed in the lattice and cannot move, so it does not conduct.

• Substance: Phosphorus trichloride ($\text{PCl}_3$)

  • Type of Bonding: Covalent Bond
  • Bonding Description: Phosphorus ($\text{P}$) and chlorine ($\text{Cl}$) are both non-metals. They form covalent bonds by sharing electrons. The phosphorus atom shares one electron with each of the three chlorine atoms, and each chlorine atom shares one electron with the phosphorus atom, allowing all atoms to achieve a stable electron configuration.
  • Property 1: $\text{PCl}_3$ has a low boiling point ($76^\circ\text{C}$).
  • Relation to Bonding: While the covalent bonds within each $\text{PCl}_3$ molecule are strong, the forces of attraction between the molecules (intermolecular forces) are weak. Only a small amount of energy is required to overcome these weak intermolecular forces, resulting in a low boiling point.
  • Property 2: $\text{PCl}_3$ does not conduct electricity.
  • Relation to Bonding: $\text{PCl}_3$ consists of neutral molecules with no free-moving ions or delocalized electrons to carry an electric charge. Therefore, it is a poor conductor of electricity.

• Substance: Calcium (Ca)

  • Type of Bonding: Metallic Bond
  • Bonding Description: Calcium is a metal. A metallic bond consists of a lattice of positively charged calcium ions ($\text{Ca}^{2+}$) surrounded by a 'sea' of delocalized valence electrons (two from each calcium atom). These electrons are not associated with any single atom but are free to move throughout the entire metal structure.
  • Property 1: Calcium is an excellent electrical conductor.
  • Relation to Bonding: The presence of delocalized electrons in the metallic structure allows them to move freely when an electric potential difference is applied. These mobile electrons can carry charge, making calcium an excellent conductor of electricity.
  • Property 2: Calcium is malleable and ductile.
  • Relation to Bonding: The 'sea' of delocalized electrons allows the layers of positive calcium ions to slide past one another without breaking the metallic bond. The delocalized electrons can simply rearrange to maintain the electrostatic attraction, allowing the metal to be hammered into sheets (malleable) or drawn into wires (ductile) without fracturing.