Scientific Method Quiz

Study Notes

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.

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

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

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.

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.

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.