Intramolecular Forces Forces (chemical bonds) within a molecule Typical value: 350 kJ/mol C-C bond Intermolecular Forces Forces between molecules Typical value: 20 kJ/mol H-bond 1 kJ/mol van der Waals

Dipole-dipole Forces If present usually dominate intermolecular interactions.

Water Held together by O-HH hydrogen bonds

Hydrogen bond donors: O-H, N-H, S-H, X-H Hydrogen bond acceptors: O, N, X, S For example: The amide hyrdrogen bond is the dominate intermolecular force in proteins.

London Dispersion Forces or van der Waals Forces

 G vap =  H vap - T  S vap What determines the B.P. of a liquid? = 0 at the B.P.  H vap = T  S vap For simple liquids, all  s vap values are about the same. So B.P. is proportional to  H vap

Four General Classifications for Solids 1. Metals Fe, Co, Ag 2. Covalent Network Solids Diamond, SiO 2 3. Ionic Solids NaCl ZnS 4. Molecular Solids I 2 Sugar

Bragg’s Law

Determination of Crystal Structures using X-Ray diffraction. Diffraction of any wave will take place when you have a grid with a spacing similar to the wavelength of the wave. X-Rays have wavelengths on the order of 1 Ångstrom. Typical value 0.71Å

Four General Classifications for Solids 1. Metals Fe, Co, Ag 2. Covalent Network Solids Diamond, SiO 2 3. Ionic Solids NaCl ZnS 4. Molecular Solids I 2 Sugar

Close Packing of Spheres

Hexagonal Close Packed Co, Ti, Mg

Body Centered Cubic Fe, Cr, V

Cubic Close Packed - Face Centered Cubic Ni, Cu, Au

Efficiency of Close Packing What fraction of the volume is occupied? f v = volume spheres in unit cell / volume of cell f v = = 0.740

The radius of Ag atom is 1.44 Å. Calculate the density. The Ag structure is fcc (ccp).

=

Close packing of spheres fills 0.74 % of the available space The remaining space can be allotted to three types of holes that occur between the spheres.

r tet = r oct = r cub = 0.732

Sodium Chloride Na +.95 Å Cl Å Table 13.7 Ratio =.95 / 1.81 =.52 r tet = r oct = r cub = 0.732

Zinc Sulfide Ratio = Zn +2 /S -2 =.35 r tet = r oct = r cub = The Zinc atoms occupy 1/2 of the tetrahedral holes

Glass Quartz

Molecular Solids C 60

Iodine I 2

Acetylene HCCH

Oxalic Acid

 G =  H - T  S = - RT ln K ln K = -(  H/R) /T +  S/R ln P = -(  H/R)(1/T) +  S/R P

Triple point torr °C