Chapter 13 The Chemistry of Solids Why does water expand as it freezes Only substance that does this Think about the nature of the liquid phase What kind of motions are allowed Think about the nature of the solid phase What kind of motions are allowed in the solid phase Liquid phase water molecules can be closer together Liquid water freezes and forms into a crystal lattice formed by hydrogen bonding interactions Nothing in between van der Waals interactions Two kinds of solid crystalline nature repeating pattern really strong intermolecular attractions ion ion dipoledipole amorphous take on any arrangement ex sulfur most plastics waxes random arrangement of atoms total intermolecular force enormous molecules probably pretty high but mostly with London dispersion forces long strands can get tangled Alcohols that have OH group probably have hydrogen bonding small alcohols will probably be crystalline long alcohol have long chains that get in the way of forming crystalline structures Primitive cubic only metal that assumes this is polonium All other metals are either body centered cubic or face centered cubic How many atoms are in a unit cell Pc 1 Bcc 2 Fcc 3 Usually cations fall into holes because they are infinitely smaller than the anion Pulonium is the only metal known to form a primitive crystal structure What is the atomic radius of a polonium atom if the density of polonium is 9 32 g cm 3 Mass 209 g 6 022E23 atoms 3 47E 22 g atom x 1 atom unit cell 3 47E 22 g unit cell Volume of unit cell 3 47E 22 g unit cell 1 cm 3 9 32 g 3 72E 23 cm 3 unit cell 37 1 cubic angstrom 3 46E 22 g 1 cm3 9 32 g 1010 angstrom 102 cm 37 1 cubic angstrom Cube root of that 3 34 Radius edge 1 67 angstrom How many radii are there along the diagonal across a fcc unit cell 4 Use Pythagorean theorem to solve diagonal How many radii are there along the diagonal across a bcc unit cell 4 What is the length of a carbon carbon bond in diamond Figuring out how to do the calculation for now not actually calculating a 3 567 angstrom Sort of has fcc unit cell shape with 4 other atoms that aren t in that unit cell shape In tetrahedral holes Will not show up on any exams Carbon atom body centered into an eight of the unit cell Bond of carbon carbon bond calculate long diagonal and figure out that half of that distance carbon carbon bond