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Download Problem #1 Put the following substances in order
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Problem #1 Put the following substances in order from lowest to highest boiling point. C2H6, NH3, F2 Problem #2 The boiling point of argon is 189.4ºC. (a) Why is it so low? (b) How does the boiling point help prove that London dispersion forces exist? (c) The boiling point of xenon is 119.9ºC. Why is it higher than that of argon? Problem #3 Which would have a higher surface tension, H2O or C6H14? Why? Would the shape of the H2O meniscus in a glass tube be the same or different than C6H14? Liquids Several properties are related to intermolecular forces 1) Surface tension resistance of a liquid to increase surface area molecules in a liquid are pulled in all directions by intermolecular forces; molecules at the surface are pulled downward and sideways; it pulls the molecules together and forms a skin ex: water (polar) on a waxed car (nonpolar) increased IMF, increased surface tension 2) Capillary action / rise rising of a liquid in a narrow tube cohesion attraction between like molecules (H2O & H2O) adhesion attraction between unlike molecules (H2O & glass) adhesion > cohesion : liquid goes up (H2O/glass) cohesion > adhesion : liquid goes down (Hg/ glass) 3) Viscosity fluids resistance to flow higher IMF, higher viscosity as temperature increases, viscosity decreases Solids Crystalline solids ordered / regular arrangement of atoms Amorphous solids disorderly arrangement (glass) Lattice 3D system of points showing the centers of atoms Unit cell smallest repeating unit of a lattice 1) simple cubic 2) bodycentered cubic 3) facecentered cubic Crystalline solids 1) Ionic electrostatic attraction NaCl, CaCO3 all ionic crystals are solids at room temperature ions have a noble gas configuration, therefore no conductivity; as melted, it has good conductivity excellent conductors as ions (aq) 2) Molecular dipoledipole / LDF S8, sugar, SO2(s) low melting point, low boiling point insulators; electrons not delocalized not thermal conductors 3) Atomic a) metallic metallic bond Cu, Na, Fe good electrical conductors excellent thermal conductors; electrons are the first particle to gain energy medium melting point solids at room temperature except mercury b) covalent covalent bonds (network or planar covalent) C (nonmetal) diamond, quartz (network covalent) sp3 graphite, mica (planar cov.) sp2 extremely high melting point melting point decreases down the table; increased bond length means less strength c) group 8A / noble gases LDF Ar Closest Packing most effecient arrangement of spheres HCP hexagonal closest packing every other layer (ABA) Mg, Zn, Cd CCP cubic closest packing facecentered cubic every third layer (ABC) Ag, Al, Ni, Pb Structure is determined by relative stability; it is governed by intermolecular forces Alloys solid solution of two or more metals has metallic properties 1) interstitial alloy holes (interstices) in the closest packed structure are occupied by small atoms 2) substitutional alloy similar size metal atoms replace Example: Why are highcarbon steels interstitial alloys while brass is a substitutional alloy? Answer: An interstitial alloy is formed when holes in the closest packed metal structure are occupied by small atoms (in high carbon steels the iron holes are filled by carbon). A substitutional alloy contains similarsized atoms of more than one element (the holes are not occupied). An example is the combination of copper and zinc to form the brass alloy.
