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Department
Chemistry
Course
CHEM 1320
Professor
Ganley
Semester
Fall

Description
Chapter 11: Intermolecular Forces and Liquids and Solids 12/2  Surface tension: energy needed to increase the surface of a liquid  by a unit area. ­Strong intermolecular forces=high surface tension Cohesion: intermolecular attraction between like molecules Adhesion: attraction between unlike molecules Viscosity: resistance to flow. “Stickiness” ­Strong intermolecular forces=high viscosity *Ice is less dense than water Crystalline solid: rigid and long­range order, atoms/molecules/ions  in a specific (predictable) positions Amorphous solid: disordered (powders) Unit cell: crystalline solid’s basic repeating structural unit At lattice points: atoms, molecules, and ions. 7 Basic Unit Cells: 1. Simple cubic: a=b=c  3 Types of Cubic Unit Cells (atoms you can see) Simple=8 atoms (none in middle) Body­centered=9 atoms (one in middle) Face­centered=12 atoms (four in middle) Coordination number: how many atoms are touching the central  atom Simple=6 Body­centered=8 Face­centered=12 Simple=1 atom/unit cell Body­centered=2 atoms/unit cell Face­centered=8 atoms/unit cell Closet Packing: Hexagonal and Cubic Hexagonal=ABABAB Cubic=ABCABC Simple: a=2r Body­centered: a=4r/√3 Face­centered: a=√8 r When silver crystalizes, it forms face­centered cubic cells. The unit  cell edge length is 409 pm. Calculate the density of silver. d=m/V V=a =(409pm) =6.83 X 10  cm ­23 3 4 atoms/unit cell in a face­centered cubic cell   107.9 g  1 mole Ag m=4 Ag atoms X ­­­­­­­­­ X ­­­­­­­­­­­­­­­ = 7.17 X 10  g22 1 mole Ag 6.022 X 10   23 ­22        m          7.17 X 10  g d= ­­­ = ­­­­­­­­­­­­­­­­­­­­­­­ = 10.5g/cm        V        6.83 X 10 cm3 *Skip 11.5 Types of Crystals: Ionic Crystals: ­Lattice points occupied by cations and anions ­Held together by electrostatic attraction ­Hard, brittle, high melting point ­Poor conductor of heat and electricity Covalent Crystals: ­Lattice points occupied by atoms ­Held together by covalent bonds ­Hard, high melting point Molecular Crystals: ­Lattice points occupied by molecules ­Held together by intermolecular forces ­Soft, low melting point ­Poor conductor of heat and electricity  Metallic Crystals: ­Lattice points occupied by metal atoms ­Held together by metallic bonds ­Soft to hard, low to high melting point ­Good conductors of heat and electricity Amorphous solid: no defined arrangement and molecular order. Glass: Optically transparent fusion, inorganic, has cooled to  rigidity without crystalizing 12/4  Phase Changes: Liquid to a gas: evaporation Gas to a liquid: condensation Equilibrium v
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