Chapter 11 Sections 7 and 8

1
Chapter 11 Sections 7 and 8

• Sherry Matthew
• Mary Same
• Rachel Wolver

2
Amorphous Solids

• Solids can be either crystalline or amorphous.
• Solids whose particles have no orderly structure,
  lack well-defined faces and shapes.
• Usually are mixtures of molecules that dont fit
  together well or are composed of large,
  complicated molecules. Ex rubber, glass

3
Crystalline Solids

• Solids whose atoms, ions, or molecules are
  ordered in well-defined arrangements, usually
  have flat surfaces with definite angles. Ex
  diamond, quartz
• melts at a specific temperature
• If a crystalline solid is melted and then rapidly
  cooled, an amorphous solid is sometimes formed if
  the atoms are unable to return to an orderly
  arrangement. Ex When quartz melts, it forms an
  amorphous solid

4
Simple CUBIC

• lattice points are at corners only

5
Body CENTERED CUBIC

• lattice point occurs at center and edges of unit
  cell

6
FACE-CENTERED CUBIC

• lattice points at center of each face and at
  each corner

7
Crystalline Structure and Ratio

• The total cation-to-anion ratio of a unit cell
  must be the same as that of an entire crystal
  (NaCl-One Na for every Cl, CaCl2, one Ca for
  every 2 Cl)
• Crystalline solids adopt the structures they do
  because they bring particles closest together and
  maximize the attractive forces between them. In
  many cases, and in metallic solids, the particles
  that make us the solids are spherical or close to
  spherical.

8
Packing

• The particles that make up crystalline solids are
  mostly spherical
• the most efficient way to pack them is to
  surround one sphere by 6 others.
• However, there are different ways to stack them
  on top of each other, and cubic close packing.
  hexagonal close packing (pg 419 OB / 469 NB)
• Coordination number number of particles
  immediately surrounding a particle in a crystal
  structure.

9
Molecular solids

• atoms/molecules held together by intermolecular
  forces.
• Since these forces are weak, these substances are
  soft and have low melting points.
• Properties also depend on the abilities of the
  molecules to pack efficiently in 3 dimensions

10
Covalent-Network Solids

• atoms are held together in large networks or
  chains by covalent bonds, covalent bonds are much
  stronger than intermolecular forces, so they are
  harder and have higher melting points (ex
  diamond, graphite)

11
Ionic Solids

• ions held together by ionic bonds, structure
  depends on the charges of the molecules

12
Metallic Solids

• consist entirely of metal atoms, have hexagonal
  close-packed, cubic close-packed (face-centered
  cubic), or body-centered cubic structures.
• Bonding is due to valence electrons that are
  delocalized throughout the entire solid (sea of
  positive ions immersed in a sea of valence
  electrons)
• strength of the bonding increases as the number
  of electrons available for bonding increases.

13
Sample Problem

• Which metal will have the higher melting point,
  sodium of chromium?
• Chromium, 6 valence electrons, bond is stronger.
• Which ionic solid will have the higher melting
  point? MgO or NaCl
• MgO has higher charges and therefore stronger
  ionic bonds