Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Solid State Solid state shows rigidity of form and maintains a definite shape. Two classes of solids: Crystalline solids: Well defined geometrical shape (cube, octahedron, tetrahedron). Amorphous solids: Geometrical shape not defined (coal, coke, glass, plastic, rubber, etc.) Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Space lattice and Unit cell Lattice Two dimensional representation of arrangement of atoms in a crystal. Space lattice Three dimensional extension of array. Unit cell A small three dimensional structural subunit of the lattice. Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Structure of unit cell Types of Unit Cell Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Primitive or simple cubic (sc): Atoms are present only at the corners of the cubic cell. Non-primitive: In these unit cells, atoms (lattice points) are present not only at the corner of unit cells but also at some other positions. Body centered cubic (bcc): Atoms are present at the corners and one at the center of the unit cell Face centered cubic (fcc): Atoms are present at the corners and one at the centre of each Face of the unit cell. End centered cubic (ecc): Atoms present at corners and at center of diagonal joining the nearest neighbors at one set of faces. Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. sc fcc bcc End-centered Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Bravais lattice Bravais showed that based on geometry, there are only 14 possible ways. There are 3 different cubic types, 2 different tetragonal types, 4 different orthorhombic types, 2 different monoclinic types, 1 rhombohedral, 1 hexagonal, 1 triclinic which constitute the 14 Bravais lattices In which similar lattice points can be arranged in regular order in 3-D space while maintaining translational symmetry. Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Crystal classes and Bravais lattices Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Cubic lattice 1.Simple cubic: No. of atoms per unit cell: 1 Density: Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. 2.Face-centered cubic: No. of atoms per unit cell: 4 Volume of the unit cell is Density: Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. 3.Body centered cubic: No. of atoms per unit cell: 2 Volume of the unit cell Density: Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Crystal structure One dimensional structure: In one dimension, the closest efficient packing is when the spheres just touch each other Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Two dimensional structure: Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. (b) Hexagonal close packing (a) Square close packing Three dimensional structure: One layer of closely packed spheres A second layer is started by placing a sphere (colored red) in a depression formed between three spheres in the first layer Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. A second layer of spheres is shown slightly transparent so we can see how the atoms are stacked over the first layer Hexagonal close packing (ABAB) Hexagonal close packing in three dimensional space Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Cubic close packing (ABCABC) Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Packing efficiency 1.Simple cubic (sc): Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. 2.Face-centered cubic (fcc): Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. 3.Body-centered cubic (bcc): Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Radius ratio rule Tetrahedral void: The space formed in the center when four spheres touch each other in a tetrahedral arrangement. Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Radius ratio rule Octahedral void: The space formed in the center when eight spheres touch each other. Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Relation between void radius and atom radius Tetrahedral void: r = R Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Octahedral void: r = R Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Braggs Law- X-Ray Structure of Crystals Braggs equation: n = 2d sin Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. CaF 2 structure Other cubic lattices: Caesium chloride, Perovskite, Antifluorite, etc Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Structure of Some Ionic Solids Examples of face-centered cubic lattices NaCl or rock salt Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Structures of Graphite and Fullerenes Graphite Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Fullerene: Buckyball Fullerene: Nanotube Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Imperfections in Solids Types of Imperfections: 1.Point defects: Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. 2.Line defects:3. Area defects4. Volume defects Point defects in ionic solids Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Schottky defect: ion-pair vacancy Frenkel defect: vacancy-interstitial Semiconductors: Role of Silicon and Germanium n- type semiconductors: Antimony, arsenic or phosphorous with 5 valence electrons when added to silicon or germanium contribute extra electrons and greatly increase conductivity. p-type semiconductors: Boron, aluminium or gallium with 3 valence electrons when added to silicon or germanium create deficiency of valence electrons, called holes. Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Liquid crystals Liquid crystals or mesogenic state exhibit properties between a conventional liquid and a solid. Classification: 1.Thermotropic liquid crystals: Transition to liquid crystalline state is achieved by raising the temperature of a solid or lowering the temperature of a liquid. Ex. p- azoxyanisole. Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. 2.Lyotropic liquid crystals: Transition to liquid crystalline state occurs as a function of concentration in solvent and temperature. Types of Mesophases (a) Nematic Liquid Crystals (b) Chiral Nematic/ Twisted Nematic/ Cholesteric Liquid Crystals (c) Smectic Liquid Crystals In homologous series, the rigid central portion plays an important role in determining liquid crystal behavior and any change in chain length affects thermal stability and other properties. Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Nematic phase Smectic phase A and C Cholesteric phase Liquid Crystal Display System Engineering Chemistry Copyright 2011 Wiley India Pvt. Ltd. All rights reserved. Schematic representation of LCD system.