Scientific Method Quiz

Solid State

• States of matter: Solids, liquids, gases
• Solids vs. other states: Solids have a definite shape and volume that aren't easily changed by temperature or pressure. Constituent particles are held together tightly by strong interparticle forces, preventing significant movement.

Types of Solids

• Crystalline solids: Regular, repeating, three-dimensional arrangement of constituent particles (atoms, ions or molecules).
  • Long-range order: The ordered arrangement of particles extends over a large area.
  • Sharp melting points: Melt at a specific, well-defined temperature.
  • Anisotropic: Properties like refractive index, thermal, and electrical conductivity vary depending on the direction of measurement (except for cubic structures).
  • Examples: Ice, diamond, graphite, NaCl (sodium chloride), metals (e.g., sodium, gold, copper), ceramics
• Amorphous solids: Random arrangement of constituent particles without long-range order.
  • Supercooled liquids: Often viewed as supercooled liquids exhibiting short-range order only.
  • Gradual softening: Melt over a range of temperatures, lacking sharp melting points.
  • Isotropic: Properties such as refractive index, conductivity, are the same in all directions.
  • Examples: Glass, plastic, rubber, tar, metallic glasses

Crystalline Solids - further classification

• Ionic crystals: Composed of ions, held together by electrostatic forces of attraction.
  • Hard and brittle: Strong forces make them hard, but they often shatter easily.
  • High melting points: Strong forces require substantial energy to break.
  • Non-conductors in solid state, but good conductors when molten/dissolved: Ions become mobile when molten or dissolved.
  • Examples: NaCl, K₂SO₄, CaF₂, KCl
• Covalent network crystals: Atoms connected by a continuous network of strong covalent bonds.
  • Very hard and incompressible: Strong bonds lead to extreme hardness.
  • High melting points: Substantial energy required to break covalent bonds.
  • Poor conductors of heat and electricity: Electrons are localized in the bonds, not free to move.
  • Examples: Diamond, quartz (SiO₂), boron nitride, carborundum
• Molecular crystals: Constituent particles are molecules or unbonded atoms, held together by weaker intermolecular forces (e.g., dipole-dipole, London dispersion, hydrogen bonds).
  • Soft with low melting points: Weaker forces are easily overcome.
  • Poor electrical conductors (good insulators): Intermolecular forces do not allow free electron movement.
  • Examples: Cl₂, CH₄, H₂, CO₂, O₂, ice, benzoic acid

Crystal Structure

• Unit cell: Smallest repeating unit of a crystal lattice.
• Lattice: Three-dimensional arrangement of points in a crystal structure.
• Basis: Group of atoms or ions associated with each lattice point.

Packing Efficiency

• Close packing: Most efficient arrangement of particles, maximizes interparticle attraction given the space.
• Simple cubic (sc): 52.4%
• Body-centered cubic (bcc): 68%
• Face-centered cubic (fcc/ccp): 74%
• Tetrahedral holes: Holes formed by four surrounding particles.
• Octahedral holes: Holes formed by six surrounding particles.

Crystal Defects

• Stoichiometric defects: The overall ratio of ions in the crystal remains the same.
  • Vacancy defect: Absence of an ion from its regular lattice site.
  • Self-interstitial defect: An ion occupies an interstitial site.
  • Schottky defect: Equal numbers of cations and anions missing from their regular lattice sites.
  • Frenkel defect: A cation is displaced from its regular lattice site to an interstitial site.
• Impurity defects: Foreign atoms occupy normal or interstitial sites.
• Nonstoichiometric defects: Ratio of constituent atoms deviates from the ideal value.
  • Metal deficiency defect: Number of metal ions is less; this is balanced by an equivalent number of extra positive charges from the same type of metal.
  • Metal excess defect: Number of metal ions is more; the additional metal ions are accommodated in the interstitial sites or the lattice sites of anions are occupied by unpaired electrons.

Electrical Properties of Solids

• Conductors: Allow easy movement of electrons.
• Insulators: Do not allow electrical conduction.
• Semiconductors: Conductivity is between that of conductors and insulators, and it increases with temperature.