2.1.3 Ionic Compounds

Formation of Ionic Compounds:

• When a chemical reaction occurs, new bonds are formed.
• Ionic compounds form by the transfer of electrons from a metal to a non-metal atom. This process creates charged particles called ions.

The Ionic Lattice

The diagrams provided show different models of the ionic lattice:

Two-Dimensional Space-Filling Model: This model illustrates how ions are arranged in a regular pattern in one layer of the lattice.

• Advantage: Clearly shows how ions are arranged in a single layer, making it easy to understand the alternating pattern of positive and negative ions.
• Limitation: Does not show how ions are arranged in the next layer or in three dimensions.

Three-Dimensional Space-Filling Model: This model shows how ions are arranged in multiple layers within the lattice.

• Advantage: Provides a more accurate representation of how closely packed the ions are within the lattice.
• Limitation: May still be misleading if it suggests there is more space between ions than there actually is.

Ball and Stick Model: This model shows the spatial arrangement of ions in three dimensions.

• Advantage: Shows the arrangement of ions in a larger section of the crystal.
• Limitation: The use of sticks for bonds can be misleading because the forces of attraction act in all directions, not just along the sticks. Additionally, it shows empty spaces between ions, which don't exist in reality.

Ionic Bonding

The ionic lattice is held together by strong electrostatic forces of attraction between oppositely charged ions. These forces act in all directions within the lattice, ensuring the structure is stable and giving ionic compounds their characteristic properties. This type of bonding is called ionic bonding.

Properties of Ionic Compounds

1. High Melting Points and Boiling Points

Ionic compounds have high melting and boiling points, which means they are typically in the solid state at room temperature.

Energy and Phase Changes:

• Melting: To melt an ionic compound, energy must be transferred to overcome some of the strong electrostatic forces of attraction between the ions.
• Boiling: To boil an ionic compound, even more energy is needed to overcome all remaining electrostatic forces.
• The More Energy Required: The higher the melting or boiling point, the more energy is required to overcome the ionic bonds. This is why ionic compounds, with their strong electrostatic attractions, have high melting and boiling points.

Explanation

• Ionic Bonding: Ionic compounds are held together by electrostatic forces between oppositely charged ions. These forces, referred to as ionic bonding, are very strong. Because a giant ionic lattice contains a large number of ions, a significant amount of energy is needed to break these bonds, resulting in high melting and boiling points.
• Strength of Ionic Bonds: The strength of the ionic bonds depends on the charge of the ions:
  • Ions with higher charges create stronger forces of attraction, requiring even more energy to overcome these forces.

2. Conducting Electricity

• Requirements for Conductivity:
  • A substance can conduct electricity if it contains charged particles, such as ions, and these particles are free to move from place to place.
• Ionic Compounds and Conductivity:
  • In the Solid State: Ionic compounds cannot conduct electricity because the ions are held in fixed positions and cannot move.
  • When Melted or Dissolved: Ionic compounds can conduct electricity when they have melted to form a liquid or when they have dissolved in water to form an aqueous solution. Both processes free the ions, allowing them to move and carry an electric current.