Chapter 12 Solids and Modern Materials

Sec$on 10.3 An Introduc+on to Structures and Types of Solids Chapter 12 Solids and Modern Materials

Sec$on 10.3 An Introduc+on to Structures and Types of Solids Solids Amorphous Solids: Disorder in the structures Glass Crystalline Solids: Ordered Structures Unit Cells Copyright Cengage Learning. All rights reserved 2

Sec$on 10.3 An Introduc+on to Structures and Types of Solids Bragg Equa$on Used to determine the interatomic spacings. nλ = 2 d sin θ n = integer λ= wavelength of the X rays d = distance between the atoms θ = angle of incidence and reflec$on Copyright Cengage Learning. All rights reserved 4

Sec$on 10.3 An Introduc+on to Structures and Types of Solids Types of Crystalline Solids Ionic Solids ions at the points of the lafce that describes the structure of the solid. Molecular Solids discrete covalently bonded molecules at each of its lafce points. Atomic Solids atoms at the lafce points that describe the structure of the solid. Copyright Cengage Learning. All rights reserved 6

Sec$on 10.4 Structure and Bonding in Metals Closest Packing Model Closest Packing: Assumes that metal atoms are uniform, hard spheres. Spheres are packed in layers. Copyright Cengage Learning. All rights reserved 9

Sec$on 10.4 Structure and Bonding in Metals The Closest Packing Arrangement of Uniform Spheres abab packing the 2 nd layer is like the 1 st but it is displaced so that each sphere in the 2 nd layer occupies a dimple in the 1 st layer. The spheres in the 3 rd layer occupy dimples in the 2 nd layer so that the spheres in the 3 rd layer lie directly over those in the 1 st layer. Copyright Cengage Learning. All rights reserved 10

Sec$on 10.4 Structure and Bonding in Metals The Closest Packing Arrangement of Uniform Spheres abca packing the spheres in the 3 rd layer occupy dimples in the 2 nd layer so that no spheres in the 3 rd layer lie above any in the 1 st layer. The 4 th layer is like the 1 st. Copyright Cengage Learning. All rights reserved 11

Sec$on 10.4 Structure and Bonding in Metals Indicated Sphere and 12 Nearest Neighbors Each sphere in both ccp and hcp has 12 equivalent nearest neighbors. Copyright Cengage Learning. All rights reserved 14

Sec$on 10.4 Structure and Bonding in Metals The Electron Sea Model A regular array of ca$ons in a sea of mobile valence electrons.

Sec$on 10.4 Structure and Bonding in Metals Band or Molecular Orbital (MO) Model Electrons are assumed to travel around the metal crystal in molecular orbitals formed from the valence atomic orbitals of the metal atoms. Copyright Cengage Learning. All rights reserved 18

Sec$on 10.4 Structure and Bonding in Metals Metal Alloys Subs$tu$onal Alloy some of the host metal atoms are replaced by other metal atoms of similar size. Inters$$al Alloy some of the holes in the closest packed metal structure are occupied by small atoms. Copyright Cengage Learning. All rights reserved 21

Sec$on 10.5 Carbon and Silicon: Network Atomic Solids Ceramics Typically made from clays (which contain silicates) and hardened by firing at high temperatures. Nonmetallic materials that are strong, brigle, and resistant to heat and agack by chemicals. Copyright Cengage Learning. All rights reserved 26

Sec$on 10.5 Carbon and Silicon: Network Atomic Solids Semiconductors n-type semiconductor substance whose conduc$vity is increased by doping it with atoms having more valence electrons than the atoms in the host crystal. p-type semiconductor substance whose conduc$vity is increased by doping it with atoms having fewer valence electrons than the atoms of the host crystal. Copyright Cengage Learning. All rights reserved 27

Sec$on 10.5 Carbon and Silicon: Network Atomic Solids Silicon Crystal Doped with (a) Arsenic and (b) Boron

Sec$on 10.6 Molecular Solids Lattice points occupied by molecules Held together by intermolecular forces Soft, low melting point Poor conductor of heat and electricity Copyright Cengage Learning. All rights reserved

Sec$on 10.7 Ionic Solids Lattice points occupied by cations and anions Held together by electrostatic attraction Hard, brittle, high melting point Poor conductor of heat and electricity CsCl ZnS CaF 2 Copyright Cengage Learning. All rights reserved

Sec$on 10.7 Ionic Solids Ionic Solids Ionic solids are stable, high mel$ng substances held together by the strong electrosta$c forces that exist between oppositely charged ions. Copyright Cengage Learning. All rights reserved 32

Sec$on 10.7 Ionic Solids Three Types of Holes in Closest Packed Structures 2) Tetrahedral holes are formed when a sphere sits in the dimple of three spheres in an adjacent layer. Copyright Cengage Learning. All rights reserved 34

Sec$on 10.7 Ionic Solids Three Types of Holes in Closest Packed Structures 3) Octahedral holes are formed between two sets of three spheres in adjoining layers of the closest packed structures. Copyright Cengage Learning. All rights reserved 35