Dot and Cross Diagrams: These are used to visualize the transfer of valence electrons. Dots represent electrons from one atom, while crosses represent electrons from the other.
Square Brackets: When drawing ions, the entire electronic structure is enclosed in square brackets to indicate that the charge is distributed over the whole ion.
Charge Notation: The final charge (e.g., ) must be written at the top right-hand corner outside the brackets.
Outer Shell Focus: Only the electrons in the highest energy level (valence shell) are typically shown, as these are the only ones involved in the bonding process.
State and Conductivity: In the solid state, ions are locked in fixed positions and cannot move, making the substance an insulator. When molten or dissolved, the lattice breaks, allowing ions to act as mobile charge carriers.
Brittleness: Ionic crystals are brittle because a sharp blow can shift layers of ions, causing like-charges to align and repel each other, shattering the crystal.
| Property | Solid State | Molten/Aqueous State |
|---|---|---|
| Structure | Rigid Lattice | Mobile Ions |
| Conductivity | Insulator | Conductor |
| Ion Mobility | Fixed | Free to move |
Predicting Charges: Always use the Periodic Table group number to determine the likely charge of an ion. Group 1 forms , Group 2 forms , Group 16 forms , and Group 17 forms .
Melting Point Comparisons: When asked to compare melting points, focus on the lattice enthalpy. Mention that higher charges and smaller ionic radii lead to stronger electrostatic attractions that require more thermal energy to overcome.
Solubility Logic: Explain solubility by referencing the formation of ion-dipole bonds. Water molecules are polar and can surround individual ions, providing enough energy to pull them out of the lattice structure.
Verification: Ensure that the total number of electrons lost by the metal atoms equals the total number of electrons gained by the non-metal atoms in your final formula.
