Metallic Electropositive: give up electrons Ionic
Electronegative/Electropositive Colavent Electronegative: want
electrons Shared electrons along bond direction Types of Primary
Chemical Bonds Isotropic, filled outer shells +-+ -+- +-+ +++ +++
+++ e- Close-packed structures Slide 2 Metals single element,
fairly electropositive elements similar in electronegativity Slide
3 cation anion Ionic Compounds elements differing in
electronegativity Slide 4 Covalent Compounds s2p2s2p2 s2p1s2p1
s2p3s2p3 sp 3 s2s2 s2p4s2p4 Slide 5 Hybridized Bonds one s + three
p orbitals 4 (x 2) electron states (resulting orbital is a
combination) sp 3 hybridization diamond also methane: CH 4
Elemental carbon (no other elements) Slide 6 Covalent Structures
Recall: zinc blende both species tetrahedral ZnS:+2 -2 GaAs:+3 -3
or sp 3 single element: C or Si or Sn diamond S Zn Slide 7 Another
way to hybridize Elemental carbon (no other elements) sp 2
hybridization graphite one s + two p orbitals 3 (x 2) electron
states (resulting orbital is a combination) one unchanged p orbital
trigonal symmetry Slide 8 Forms of carbon with sp 2 bonds Nobel
Prize Physics, 2010 Nobel Prize Chemistry, 1996 Graphene Fullerene
Nanotube source: Wikipedia Graphite* *
http://www.electronics-cooling.com/assets/images/2001_August_techbrief_f1.jpg
Slide 9 Structural Characteristics Metals Close-packed structures
(CN = 12) Slightly less close-packed (CN = 8) Ionic structures
Close-packed with constraints CN = 4 to 8, sometimes 12 Covalent
structures Not close-packed, bonding is directional Any can be
strongly or weakly bonded (T m ) Slide 10 Diamond vs. CCP 8
atoms/cell, CN = 44 atoms/cell, CN = 12 tetrahedral sites filled
Slide 11 Computing density Establish unit cell contents Compute
unit cell mass Compute unit cell volume Unit cell constant, a,
given (or a and c, etc.) Or estimate based on atomic/ionic radii
Compute mass/volume, g/cc Example: NaCl Contents = 4 Na + 4 Cl Mass
= 4(atom mass Na + atomic mass Cl)/N o Vol = a 3 Units = Avogardos
# Cl Na Slide 12 Single Crystal vs. Polycrystalline Rb 3 H(SO 4 ) 2
Ba(Zr,Y)O 3- Periodicity extends uninterrupted throughout entirety
of the sample External habit often reflects internal symmetry
Regions of uninterrupted periodicity amalgamated into a larger
compact = grains delineated by grain boundaries Quartz (SiO 2 )
Diamond Slide 13 Slide 14 Isotropic vs. Anisotropic *
http://www.electronics-cooling.com/assets/images/2001_August_techbrief_f1.jpg
graphite*diamond polycrystalline averaging Slide 15 Metallic
Electropositive: give up electrons Ionic
Electronegative/Electropositive Colavent Electronegative: want
electrons Shared electrons along bond direction Types of Bonds
Types of Materials Isotropic, filled outer shells +-+ -+- +-+ +++
+++ +++ e- Close-packed structures Slide 16 H Whats Missing? Long
chain molecules with repeated units Molecules formed by covalent
bonds Secondary bonds link molecules into solids C C H H H methane
C H many units
http://en.wikipedia.org/wiki/File:Polyethylene-repeat-2D.png Slide
17 Polymer Synthesis Traditional synthesis Initiation, using a
catalyst that creates a free radical Propagation Termination R +
C=C R C C + C=C R C C + C CR unpaired electron C=C H H H H R C C RC
C C C R (C-C) n R Slide 18 Polydispersity Traditional synthesis
large variation in chain length number average # of polymer chains
molecular weight # of polymer chains of M i total number of chains
molecular weight weight average weight of polymer chains of M i
total weight of all chains width is a measure of polydispersity =
weight fraction Degree of polymerization Average # of mer
units/chain Average chain molecular weight by number by weight mer
molecular weight Slide 19 Polydispersity Traditional synthesis
large variation in chain length number average # of polymer chains
molecular weight # of polymer chains of M i total number of chains
molecular weight weight average weight of polymer chains of M i
total weight of all chains width is a measure of polydispersity =
weight fraction Degree of polymerization Average # of mer
units/chain Average chain molecular weight by number by weight mer
molecular weight Slide 20 New modes of synthesis Living
polymerization Initiation occurs instantaneously Chemically
eliminate possibility of random termination Polymer chains grow
until monomer is consumed Each grows for a fixed (identical) period
Slide 21 Polymers Homopolymer Only one type of mer Copolymer Two or
more types of mers Block copolymer Long regions of each type of mer
Bifunctional mer Can make two bonds, e.g. ethylene linear polymer
Trifunctional mer Can make three bonds branched polymer Slide 22
Polymer Configurations Linear Branched Cross-linked C CCC C C CC C
C = C H H H H Slide 23 Polymers C CCC C C CC C C = C H H H H 109.5
H out H in Placement of side groups is fixed once polymer is formed
Example side group: styrene R = R Slide 24 C CCC C C CC C R RR R C
= C H H Cl H Isotactic C CCC C C CC C R RRR Syndiotactic CCCC C C
CC C R RR R Atactic Slide 25 Thermal Properties Thermoplastics Melt
(on heating) and resolidify (on cooling) Linear polymers Thermosets
Soften, decompose irreversibly on heating Crosslinked Crystallinity
Linear: more crystalline than branched or crosslinked Crystalline
has higher density than amorphous Slide 26 Formal Crystallography
Crystalline Periodic arrangement of atoms Pattern is repeated by
translation Three translation vectors define: Coordinate system
Crystal system Unit cell shape Lattice points Points of identical
environment Related by translational symmetry Lattice = array of
lattice points a b c space filling defined by 3 vectors
parallelipiped arbitrary coord system lattice pts at corners +
Slide 27 hcp ccp (fcc) bcc Hexagonal unit cell Specify: a, c
Hexagonal implies: | a 1 | = | a 2 | = a = 120 = = 90 Cubic unit
cells Specify: a Cubic implies: | a 1 | = | a 2 | = | a 3 | = a = =
= 90 But the two types of cubic unit cells are different! Slide 28
6 or 7 crystal systems 14 lattices a, b, c, , , all arbitrary a, b,
c arbitrary a, c arbitrary b = a = = 90 a arbitrary; a = b = c
arbitrary; = = C or A centered for = arbitrary a, c arbitrary a
arbitrary a, b, c arbitrary = = 90 Slide 29 Centered Lattices b a b
a b a conventional choice unconventional choice a b both are
primitive cells unconventional is primitive conventional is
centered unconventional choice conventional choice Slide 30 More on
Lattices X Slide 31 X Slide 32 Lattice types of some structures
Slide 33 Lattice types? BCC Metal CsCl Structure How many lattice
points per unit cell? Slide 34 Lattice types? Zinc blende
(sphaelerite) Fluorite Slide 35 Lattice types? Diamond Perovskite:
AMO 3 A M O
