Paper XII (IVSemester) Presentation ON CRYSTAL STRUCTURE Paper XII (IVSemester) By Dr. Kshirsagar S.V.

Ionic solids Molecular Solids Covalent Solids Metallic solids STRUCTURES OF CRYSTALLINE SOLID TYPES Molecular Solids Covalent Solids Ionic solids Metallic solids Na+ Cl-

QUARTZ DIAMOND GRAPHITE

CRYSTAL STRUCTURE Crystal structure is the periodic arrangement of atoms in the crystal. Association of each lattice point with a group of atoms(Basis or Motif). Lattice: Infinite array of points in space, in which each point has identical surroundings to all others. Space Lattice  Arrangements of atoms = Lattice of points onto which the atoms are hung. Space Lattice + Basis = Crystal Structure = • • • + Elemental solids (Argon): Basis = single atom. Polyatomic Elements: Basis = two or four atoms. Complex organic compounds: Basis = thousands of atoms.

a a ONE DIMENTIONAL LATTICE ONE DIMENTIONAL UNIT CELL a UNIT CELL : Building block, repeats in a regular way a a

TWO DIMENTIONAL LATTICE

TWO DIMENTIONAL UNIT CELL TYPES b a  b,   90° a  b,  = 90° a = b,  = 90° a = b,  =120°

EXAMPLE OF TWO DIMENTIONAL UNIT CELL

TWO DIMENTIONAL UNIT CELL POSSIBILITIES OF NaCl

THREE DIMENTIONAL UNIT CELLS / UNIT CELL SHAPES 1 7 2 3 4 5 6

LATTICE TYPES Primitive ( P ) Body Centered ( I ) Face Centered ( F ) C-Centered (C )

BRAVAIS LATTICES 7 UNIT CELL TYPES + 4 LATTICE TYPES = 14 BRAVAIS LATTICES

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