Ionic bonding and structure

• ionic bonding is the electrostatic attraction between positive and negative ions
• ionic bonding holds together cations and anions in ionic compounds
• Each ion attracts oppositely charged ions in all directions. The result is a giant ionic lattice structure.
• A giant ionic lattice is a key structural feature of all ionic compounds
• Most ionic compounds are solids at room temp because high temps are needed to provide the large quantity of energy needed to overcome the strong electrostatic forces of attraction between the oppositely charged ions. Therefore, most ionic compounds have high melting and boiling points.
• Melting points are greater for lattices that contain ions with greater ionic charges, as there is stronger attraction between ions. Ionic attraction also depends on the size of the ions
• Many ionic compounds dissolve in polar solvents like water. Polar water molecules break down the lattice and surround each ion in solution.

  In a compound made of ions with large charges, the ionic attraction may be too strong for water to be able to break down the lattice structure. This compound will not be very soluble
• Solubility requires two main processes:

  • the ionic lattice must be broken down
  • water molecules must attract and surround the ions
• The solubility of an ionic compound in water depends on the relative strengths of the attractions within the giant ionic lattice and the attractions between the ions and water molecules
• In the solid state, an ionic compound does not conduct electricity but once melted or dissolved in water it does
• Ionic compound in the solid state:

  • the ions are fixed in position in the giant ionic lattice
  • there are no mobile charge carriers
  • no conductivity of electricity
• Ionic compound when liquid or dissolved in water:

  • the solid ionic lattice breaks down
  • the ions are now free to move as mobile charge carriers
  • electricity is conducted
• Most ionic compounds:

  • have high melting and boiling points
  • tend to dissolve in polar solvents such as water
  • conduct electricity only in the liquid state or in aqueous solution