Overview
This lecture covers the advantages and limitations of different diagram types used to represent molecules and giant ionic structures.
Dot and Cross Diagrams
- Dot and cross diagrams use different symbols to show electrons from each atom.
- They make it clear which electrons come from which atom.
- These diagrams do not show the actual shape of the molecule.
2D Stick Diagrams
- 2D stick diagrams use lines to represent covalent bonds.
- They do not indicate which atom provided which electron in a bond.
- They do not show non-bonding outer electrons.
- They do not accurately represent the shape of the molecule.
3D Stick Diagrams
- 3D stick diagrams can show the molecular shape.
- They still do not indicate the origin of electrons or non-bonding electrons.
Representing Giant Ionic Structures
- Ball and stick diagrams display ions in three dimensions.
- These diagrams falsely show ions as widely spaced instead of closely packed.
- Space-filling diagrams show ions as tightly packed, closer to reality.
- Space-filling diagrams make it hard to see the 3D arrangement.
- Both diagram types show only a small part of the whole crystal lattice, making the structure appear smaller than it is.
Key Terms & Definitions
- Dot and Cross Diagram — a molecular diagram using dots and crosses to represent electrons from different atoms.
- 2D Stick Diagram — a flat representation showing covalent bonds as lines.
- 3D Stick Diagram — a three-dimensional view showing the molecular shape.
- Ball and Stick Diagram — a 3D model of giant ionic lattices showing ions as balls connected by sticks.
- Space-Filling Diagram — a model showing how closely ions or atoms are packed in a structure.
- Giant Ionic Lattice — a large, repeating three-dimensional structure of ions.
Action Items / Next Steps
- Practice questions on this topic as found in the revision workbook.