Crystal Structures Flashcards
What is a Crystal?
Solids that contain particles in a regular arrangement known as a lattice.
What are the 4 groups crystal lattices are classified in to?
Ionic Crystals
Metallic Crystals
Molecular (Simple Covalent) Crystals
Macromolecular (giant covalent) structures
How are ionic crystals structured?
Positive and Negative Ions, held together in a giant ionic lattice by strong electrostatic attraction between oppositely charged ions.
What are the properties of Ionic Crystals and why?
- Hight m.p: Strong electrostatic attraction between oppositely charged ions
- Only conduct molten/ in solution: Ions free to move and carry a charge in liquid state
- Hard, but brittle: Force can move ions and produce contact between like charges causing repulsion
- Often dissolve in water: Ions become solvated and surrounded by water molecules.
What is a metallic crystal?
A giant lattice of positive ions held together by a sea of delocalised electrons
What are the properties of metallic crystals and why do they have them?
- High m.p & b.p: Strong electrostatic attraction between metal ions and the delocalised sea of electrons
- Conduct electricity solid: Free moving electrons that can carry a charge through the structure.
- Malleable and Ductile: Metal ions slide past each other, but retain lattice structure and metallic properties.
- Insoluble: Water molecules can’t break up the metallic bonding, so metal ions can’t become solvated.
What is a molecular crystals (simple covalent)?
Individual molecules held together by weak intermolecular forces.
Properties of molecular crystals?
- Low m.p, soft and easily breakable: Only weak van der waals forces between molecules so only a small amount of energy is needed to overcome these.
- Doesn’t conduct electricity: No free moving electrons/ions so nothing can carry the charge.
What is a macromolecular (giant covalent) structure?
A giant arrangement of atoms joined by covalent bonds.
What is the structure of Diamond?
Interlocking tetrahedra of Carbon atoms
Properties of Diamond?
V.High m.p & Very Hard: many strong covalent bonds holding structure together, so lots of energy needed to break these bonds
- Non-conductor: No free moving electrons/ ions so nothing to carry charge.
Structure of Graphite?
Layered structure of Carbon atoms
Properties of Graphite?
- Very high m.p: Many strong covalent bonds holding structure together, so takes lots of energy to break these bonds.
- Soft, flaky & slippery: Has a layered structure with delocalised electrons between layers, so layers can slide.
- Conducts electricity: Delocalised electrons between layers that are free to move & carry a charge.
