solids
Download
Skip this Video
Download Presentation
Solids

Loading in 2 Seconds...

play fullscreen
1 / 25

Solids - PowerPoint PPT Presentation


  • 97 Views
  • Uploaded on

Solids. Ch.13. Solids. Fixed, immobile (so to speak) Symmetry Crystals So what’s the inner order?. Unit Cells. Unit cell = smallest repeating unit containing all symmetry characteristics Unit cell reflects stoichiometry of solid

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Solids' - talbot


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
solids

Solids

Ch.13

solids1
Solids
  • Fixed, immobile (so to speak)
  • Symmetry
  • Crystals
  • So what’s the inner order?
unit cells
Unit Cells
  • Unit cell = smallest repeating unit containing all symmetry characteristics
  • Unit cell reflects stoichiometry of solid
  • Several unit cell types possible, but atoms or ions placed at lattice points or corners of geometric object
crystal lattices
Crystal Lattices
  • 3D unit cells built like legos 
  • Crystal Lattice = arrangement of units cells
  • seven 3D units cells found
  • Simplest = Cubic Unit Cell (equal length edges meeting at 90° angles)
  • Each face part of 2 cubes
  • Each edge part of 4 cubes
  • Each corner part of 8 cubes
cubic unit cell
Cubic Unit Cell
  • 3 types:
  • 1)Primitive or Simple Cubic (SC)
  • 2) Body-Centered Cubic (BCC)
  • 3) Face-Centered Cubic (FCC)
cubic unit cell cont
Cubic Unit Cell (cont.)
  • Similarity:
  • Same ions/atoms/molecules at each corner
  • Difference:
  • BCC/FCC have more items at other locations
  • BCC has same item in center of cube
  • FCC has same item centered on each side of cube
which metals have which crystal lattices
Which metals have which crystal lattices?
  • Simple cubic: Po
  • BCC: GI, 3B, 4B, Ba, Ra, Fe
  • FCC: VIIIB, IB, Al, In, Pb
how many atoms per unit cell
How many atoms per unit cell?
  • SC: each atom shared by 8 cubes
  • 8 corners of cube  1/8 of each corner atom w/in unit cell = 1 net atom/unit cell
more on sc
More on SC
  • Each atom touches one another along edge
  • Thus, each edge = 2r
  • Coordination number (# of atoms with which each atom is in direct contact) = 6
  • Packing efficiency = fraction of volume occupied = 52%
how many atoms per unit cell cont
How many atoms per unit cell? (cont.)
  • BCC: 2 net atoms w/in unit cell (SC + 1 in center)
  • FCC: 6 faces of cube  ½ atom w/in unit cell = 3 atoms + 1 atom (SC) = 4 net
more on bcc
More on BCC
  • Each atom does not touch another along edge
  • However, atoms touch along internal diagonal
  • Thus, each edge length = 4r/3
  • Let’s derive this…
  • Coordination number (# of atoms with which each atom is in direct contact) = 8
    • Central atom touches 8 atoms
  • Packing efficiency = fraction of volume occupied = 68%
more on fcc
More on FCC
  • Each atom does not touch another along edge
  • However, atoms touch along face diagonal
  • Thus, each edge length = (22)r
  • Let’s derive this…
  • Coordination number (# of atoms with which each atom is in direct contact) = 12
  • Packing efficiency = fraction of volume occupied = 74%
problems
Problems
  • Eu is used in TV screens. Eu has a BCC structure. Calculate the radius of a europium atom given a MW = 151.964 g/mol, a density of 5.264 g/cm3.
  • Iron has a BCC unit cell with a cell dimension of 286.65 pm. The density of iron is 7.874 g/cm3 and its MW = 55.847 g/mol. Calculate Avogadro’s number.
ccp and hcp efficiency in stacking
CCP and HCP: Efficiency in Stacking
  • CCP = Cubic Close-Packing (it’s FCC)
  • HCP = Hexagonal Close-Packing
  • 74% packing efficiency
structures of ionic solids
Structures of ionic solids
  • Take a SC or FCC lattice of larger ions
  • Place smaller ions in holes w/in lattice
  • Smallest repeating unit = unit cell
slide17
CsCl
  • SC unit cell
  • Cs+ in center of cube  Cubic hole
  • Surrounded by 1 Cl- (in 8 parts)
    • 1 Cs+ : 1 Cl-
  • Coordination # = 8
  • Why SC and not BCC?
  • Because ion in center different from lattice pt ions
slide18
LiCl
  • Notice: Li+ has octahedral geometry
  • Thus, cation in octahedral hole (between 6 ions)
    • Coordination # = 6
  • FCC
slide19
NaCl
  • FCC
  • Lattice has net 4 Cl-/unit cell
    • (8x1/8)+(6x1/2) = 4
  • 1 Na+ in center of unit cell
  • 3 Na+ along edges of unit cell
    • (12x1/4) = 3
    • Thus, net total of 4 Na+ ions
  • Total 4 Cl- : 4 Na+  1:1
tetrahedral holes
Tetrahedral holes
  • Each ion surrounded by 4 other oppositely-charged ions
  • Unit cell: 4 of each ion  total 8 ions
  • Coordination # = 4
  • 8 tetrahedral holes in FCC unit cell
    • 4 by Zn2+ and 4 by S2-
  • Zn2+ occupies ½ of tetrahedral holes and surrounded by 4 S2-
  • S2- forms FCC unit cell
other types of solids network solids
Other Types of Solids: Network Solids
  • Array of covalently bonded atoms
  • Graphite, diamond, and silicon
  • The latter two  sturdy, hard, & high m.p.’s
other types of solids amorphous solids
Other Types of Solids: Amorphous Solids
  • Glass & plastics
  • No regular structure
    • Break in all sorts of shapes
  • Long range of m.p.’s
ad