《结构化学 Structural Chemistry》课程教学资源（课件讲稿）Chapter 7 Introduction to Crystallography

Chapter 7Introduction to Crystallography7.1 Periodicity and lattices of crystal structure7.2 Symmetry in crystal structures7.3 X-ray diffraction of crystals7.4 Quasi-crystal, liguid crystal and amorphous

Chapter 7 Introduction to Crystallography 7.1 Periodicity and lattices of crystal structure 7.2 Symmetry in crystal structures 7.3 X-ray diffraction of crystals 7.4 Quasi-crystal, liquid crystal and amorphous

CrystallineSubstances:e.g.,Diamond and TableSaltDiamonds

Diamonds Crystalline Substances: e.g., Diamond and Table Salt

7.1periodicity and lattices of crystal structure7.1.1 The characteristics of crystal structure1.Afewdefinitions:Solids canbe divided into twoprimary categoriescrystalline solids and amorphous solidsCrystallineSolidsarebuiltfromatomsormoleculesarranged in a periodic manner in space, e.g., rock salt anddiamond.Amorphous Solids possess short-range order only.Theyare not related through symmetry, e.g. glass, rosin, amberglass.>Short-Range Order:Fixedbond lengths and angles> Long-Range Order:Associated with a lattice point

7.1 periodicity and lattices of crystal structure 7.1.1 The characteristics of crystal structure 1. A few definitions: • Solids can be divided into two primary categories, crystalline solids and amorphous solids. • Crystalline Solids are built from atoms or molecules arranged in a periodic manner in space, e.g., rock salt and diamond. • Amorphous Solids possess short-range order only. They are not related through symmetry, e.g. glass, rosin, amber glass.  Short-Range Order: Fixed bond lengths and angles  Long-Range Order: Associated with a lattice point

Crystalsare solids that are built from atoms ormolecules arrangedin a periodic mannerin spaceCrystallinevs.AmorphousofSiO2Quartz:(Crystalline)C.N.:Glass:(Amorphous)BothShortandLongRangeOrderShortRangeOrderOnlySi= 4Oxygen0=2SiliconOShort range order: fixed bond lengths and anglesduetothe bonding nature of constituent atoms

Crystals are solids that are built from atoms or molecules arranged in a periodic manner in space. Short range order: fixed bond lengths and angles due to the bonding nature of constituent atoms. C.N.: Si = 4 O = 2

2.Fundamental characteristicsof crystal Spontaneous formation of polyhedral shapesaF+V=E+2DodecahedronIcosahedronCube20facesand 12verticesNo5-foldaxisisallowedinasingle crystal!TetrahedronOctahedronb)Uniformity: periodic distribution of atoms/molecules

2. Fundamental characteristics of crystal a) Spontaneous formation of polyhedral shapes F + V = E + 2 b) Uniformity: periodic distribution of atoms/molecules No 5-fold axis is allowed in a single crystal!

Single crystal gold bead withnaturallyformedfacets

Single crystal gold bead with naturally formed facets

l0i0HG100nm100nmHRTEM images of hollow beads

HRTEM images of hollow beads

·AnisotropyDifferent periodicity and densityfor different direction2150 g/mm2Conductivity1150 g/mm2Graphite570 g/mmNaCI

•Anisotropy NaCl 570 g/mm2 1150 g/mm2 2150 g/mm2 Graphite Conductivity Different periodicity and density for different direction

·DefinitesharpmeltingpointsSymmetry:crystal shape (macroscopic)latticearrangement(microscopic)·X-raydiffractionbycrystals:atomic distances match the wavelength of x-ray

• Symmetry: crystal shape (macroscopic) lattice arrangement (microscopic) •Definite sharp melting points •X-ray diffraction by crystals: atomic distances match the wavelength of x-ray. t T

Sodium Chloride: Solid and Crystal structure

Sodium Chloride: Solid and Crystal structure