Solids

1
Solids
2
Phase Diagrams

• Show most stable phase as a function of pressure
  and temperature
• Determine vapor pressure, boiling point, melting
  point, critical point

3
Carbon Dioxide

• Cannot exist as liquid at ordinary pressures
• Melting point increases with increasing pressure

4
Water

• Has abnormally high boiling point
• Melting point decreases with increasing pressure

5
Water

• The diagram to the left shows several different
  solid phases.
• Each solid phase has a different lattice
  structure.

6
Closest-packed structures

• 12 nearest neighbors Coordination number is 12
• Hexagonal abababab...
• Cubic abcabc

7
Simple Crystal Structures

• Cubic structures
• Simple cube
• Coordination number is 6
• Body-centered cubic
• Coordination number is 8
• Face-centered cubic
• Present in cubic closest-packed structure
• Coordination number is 12

8
Unit Cells

• Simple cube
• 1 net atom per cell
• Body-centered cubic
• 2 net atoms per cell
• Face-centered cubic
• 4 net atoms per cell

9
Density of Nickel

• Face-Centered Cubic Structure
• Edge Length 0.3524 nm (X-Ray Data)
• The Volume of the cube is given by
• V (0.3524 nm)3 0.04376 nm3
• V (0.04376 nm3) (1 cm / 10-7 nm)3 4.376 x
  10-23 cm3
• For a FCC structure, there are 4 atoms per unit
  cell. The Ni mass per unit cell is therefore 4
  times the mass of a single atom.
• m (58.59 g/mol) (1 mol / 6.022 x 1023 atoms)
  9.746 x 10-23 g / atom
• mcell 4 atoms (9.746 x 10-23 g / atom) 3.900
  x 10-22 g
• The density is then
• d mcell / V 3.900 x 10-22 g / 4.376 x 10-23
  cm3
• d 8.909 g / cm3

10
Ionic Structures

• NaCl
• Cubic closest-packed of Cl- with Na in
  octahedral holes
• FCC with counterions in holes
• CsCl2
• Cl- arranged as simple cube with Cs2 in center