Coulombic Attraction: The strength of the bond is governed by Coulomb's Law, where the force is proportional to the product of the charges and inversely proportional to the square of the distance between them: .
Electronegativity Difference: Ionic bonds typically form when the difference in electronegativity between two atoms is large (usually on the Pauling scale), ensuring a complete transfer of electrons rather than sharing.
Lattice Energy: This is the energy released when gaseous ions come together to form one mole of a solid ionic compound. Higher charges and smaller ionic radii result in greater lattice energy and stronger bonds.
Lewis Dot Diagrams: Use dots or crosses to represent valence electrons. Show the transfer with an arrow from the metal to the non-metal.
Ion Notation: After transfer, place the resulting ions in square brackets with the charge written as a superscript outside the bracket (e.g., and ).
Charge Neutrality: The total positive charge from cations must exactly equal the total negative charge from anions. For example, if a cation has a charge and an anion has a charge, two anions are required for every one cation.
Group Trends: Use the Periodic Table groups to predict ion charges: Group 1 forms , Group 2 forms , Group 16 forms , and Group 17 forms .
High Melting/Boiling Points: The giant lattice is held together by strong electrostatic forces in all directions, requiring significant thermal energy to break the bonds and change state.
Brittleness: When an external force is applied, layers of ions may shift. If like-charged ions (e.g., positive next to positive) align, the resulting electrostatic repulsion causes the crystal to shatter.
Solubility: Many ionic compounds are soluble in polar solvents like water. The partial charges of water molecules attract the ions, pulling them out of the lattice into solution (hydration).
Check the Brackets: When drawing Lewis diagrams for ionic bonds, always include square brackets around the ions. Failing to do so is a common mistake that suggests the bond is covalent.
Verify Charge Balance: Always sum the charges in your final formula; if the result is not zero, the formula is incorrect. For example, and must combine as to reach a net charge of zero ( and ).
State of Matter Matters: If a question asks about electrical conductivity, check the state. Solid = No; Molten/Aqueous = Yes. Always explain this by mentioning the mobility of ions.
Radius and Charge: If comparing melting points, look at the ion charges first (higher charge = higher melting point). If charges are the same, look at the size (smaller ions = closer together = stronger attraction).
