9701 · 4.2
Bonding and structure
The way particles are bonded and arranged on a microscopic level dictates a substance's real-world properties. Understanding the four main structure types allows us to predict how materials will behave.
Need to know
What you need to know
- **High Melting and Boiling Points:** A large amount of energy is required to overcome the strong electrostatic forces holding the ions together in the lattice.
- **Brittle:** If a force is applied, layers of ions may shift. This brings ions with like charges alongside each other, causing strong repulsion that shatters the crystal.
- **Electrical Conductivity:** Do not conduct when solid as ions are in fixed positions. They conduct when molten or dissolved in a polar solvent (like water) because the ions are mobile and can act as charge carriers.
- **Solubility:** Often soluble in polar solvents like water. The polar water molecules can surround the individual ions (hydration), overcoming the lattice energy and allowing the compound to dissolve.
Explanation
Structure is Everything
- Giant ionic lattices like NaCl have strong electrostatic forces between ions, requiring lots of energy to break. This causes high melting points and they often dissolve in water.
- Giant covalent structures like diamond have a vast network of strong covalent bonds. This makes them extremely hard with very high melting points.
- Giant metallic structures have a lattice of positive ions in a 'sea' of delocalised electrons. These mobile electrons allow metals to conduct electricity and heat, and the layers of ions can slide, making them malleable.
- Simple molecular substances like H₂O or CO₂ have weak intermolecular forces between individual molecules. Little energy is needed to overcome these forces, resulting in low melting and boiling points.