Notes on Physical Chemistry in Crystalline Structures

Introduction to Physical Chemistry

  • Subject: Physical Chemistry (Fizikalna kemija)
  • Duration: 2 hours

Learning Materials

  • Materials prepared to facilitate independent study, related to General Chemistry 1.
  • Includes revision questions at the end and support from teachers for distant learning.
  • Encouragement for positive learning experience.

Definition of a Crystal

  • Definition: Solids that have a defined geometric shape formed by the precise arrangement of particles.
  • Characteristics:
    • Sharp edges
    • Smooth surface

Types of Solid Materials

  1. Amorphous Materials

    • Characteristics: Solids without a defined shape; very short-range order like undercooled liquids.
    • Examples: Glass, Quartz.

  2. Crystalline Materials

    • Characteristics: Solids with a regular geometric shape.

Symmetry in Crystals

  • Axis of Symmetry: Imaginary line about which the crystal can be rotated.
  • Center of Symmetry: Imaginary point in the center of the crystal dividing all geometric elements in half.
  • Plane of Symmetry: Imaginary plane dividing crystal into two equal halves.

Lattices in Crystalline Structures

  • Infinite Atomic Lattice: Atoms bonded with covalent bonds.
  • Infinite Ionic Lattice: Composed of ions connected by ionic bonds.
  • Infinite Metallic Lattice: Comprised of metal atoms bonded by metallic bonds.
  • Molecular Lattices: Crystal lattices of molecules bonded by intermolecular forces.

Properties of Lattices

  1. Covalent Lattice

    • High melting and boiling points due to strong covalent bonds.

  2. Ionic Lattice

    • Strong bonds with high melting and boiling points.

  3. Metallic Lattice

    • Made up of metal atoms; high melting points due to metallic bonding.

  4. Molecular Lattice

    • Weak forces, leading to low melting and boiling points.

Crystal System Properties

  • Cubic systems (e.g., Pyrite, FeS):
    • All side lengths equal and all angles at 90 degrees.
  • Tetragonal systems (e.g., Zircon, ZrSiO):
    • Two side lengths equal, angles at 90 degrees.
  • Hexagonal systems (e.g., Quartz):
    • Specific angle arrangements with side lengths not equal.
  • Rhombohedral systems (e.g., Calcite, CaCO3):
    • Unequal lengths, with specific angle arrangement.

Types of Crystals

  1. Ionic Crystals: Formed from ions, examples include NaCl.
  2. Molecular Crystals: Composed of molecules, examples with different interaction forces.
  3. Covalent Crystals: Bonded strongly by covalent bonds.
  4. Metallic Crystals: Made from metal atoms with electron clouds facilitating bonding.

Melting and Solubility Properties

  • Ionic Crystals: High melting points, soluble in polar solvents (e.g., NaCl in water).
  • Molecular Crystals: Low melting points, soluble in organic solvents, do not conduct electricity.
  • Covalent Crystals: Very high melting points; insoluble in most solvents, do not conduct electricity.
  • Metallic Crystals: High melting points, conductive in solid and liquid states due to mobile electrons.

Hydration in Ionic Crystals

  • Hydration: Process by which ions are surrounded by water molecules during dissolution; essential for ionic conductivity in solution.

Fragility in Ionic Crystals

  • Brittleness: Property of ionic crystals that causes them to break along certain planes when subjected to mechanical force.

Polymorphism

  • Definition: Occurrence of the same chemical compound in multiple crystal forms (e.g., Calcite vs. Aragonite).

Density and Unit Cell Calculations

  • Example calculations for the density of materials like sodium and a-polonium, understanding unit cells, radii of atoms, and their arrangements in different lattice types (simple cubic, face-centered cubic, etc.).
  • Importance of the radius of an atom in determining the lattice structure and density calculations.

Conclusion

  • Understanding of crystal properties and behavior is essential for comprehending aspects of physical chemistry, especially in applications related to material science and engineering.