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NIU CHEM 211 - Characteristics of Liquids and Structural Features of Solids
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CHEM 211 1st Edition Lecture 5Outline of Last Lecture I. The Hydrogen BondII. Polarizability and Induced DipolesIII. Dispersion (London) ForcesIV. Molecular shape, Intermolecular Contact, and Boiling PointOutline of Current Lecture I. Surface TensionII. CapillarityIII. ViscosityIV. Properties of WaterV. The Unusual Density of Solid WaterVI. Structural Features of SolidsVII. Packing Efficiency and the Creation of Unit CellsVIII. Types and Properties of Crystalline SolidsIX. Bonding in Solids II: Band TheoryX. Conductivity of Solids and the Size of the Energy GapCurrent LectureI. Surface TensionA. A surface molecule experiences a net attraction downward. This causes a liquid surface to have the smallest area possible.B. An interior molecule is attracted by others on all sides.C. Surface tension is the energy required to increase the surface area of a liquid. The stronger the forces between the particles the higher the surface tension.II. CapillarityA. High capillarity means water rises through the tiny spaces between soil particles, so plant roots can absorb deep groundwater during dry periods.a) Water displays a concave meniscus.b) Mercury displays a convex meniscus.III. ViscosityB. Viscosity is resistance of a fluid to flow.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.C. Results from intermolecular attractionsthat impede the movement of molecules around and past each other.D. Both gasesand liquids flow, but liquid viscosities are much higher because the much shorterdistances between their particles result in many more points for intermolecular forcesto resist the flow of nearby molecules.IV. Properties of WaterA. Each H2O molecule can form four H bonds to other molecules, resulting in a tetrahedral arrangement.B. Hydrogen bonding is also responsible for water’s high surface tension and high capillarity.C. Water has the highest surface tension of any liquid.V. The Unusual Density of Solid WaterA. Ice has a tetrahedral arrangement of H-bonded water molecules.B. The large spaces within ice make the solid less dense than the liquid and explainthe negative slope of the solid-liquid line in the phase diagram for water.VI. Structural Features of SolidsA. The collection of points forms a regular pattern called the crystal lattice.B. A key parameter of any lattice is the coordination number, the number of nearest neighbors of a particle.C. Unit Cell is the smallest portion that gives the crystal if it is repeated in all directions.D. Solids are divided into two categoriesa) Crystalline solids have well defined shapes due to the orderly arrangement of their particles.b) Amorphous solids lack orderly arrangement and have poorly defined shapes.E. A crystal is composed of particles packed in an orderly three-dimensional array called the crystal lattice.VII. Packing Efficiency and the Creation of Unit CellsA. Most basic unit and least volume consuming repeating structure of any solid.a) Simple cubic:Atoms/unit cell = (⅛ x 8) = 1b) Body-centered cubic:Atoms/unit cell = (⅛ x 8) + 1 = 2c) Face-centered cubic:Atoms/unit cell = (⅛ x 8) + (½ x 6) = 4B. Hexagonal unit cell: If we place the third layer of spheres over the orangespaces they lie directly over the spheres in layer a.C. Face-centered unit cell: If we place the third layer of spheres over the white spaces in layer b, the placement is differentfrom layers a and b.VIII. Types and Properties of Crystalline SolidsA. Atomic solids consist of individual atoms held together only by dispersion forces.B. Molecular solids consist of individual molecules held together by various combinations of intermolecular forces.C. Ionic solids consist of a regular array of cations and anions.D. Metallic solids exhibit an organized crystal structure.E. Network Covalent solids consist of atoms covalently bonded together in a three-dimensional network.IX. Bonding in Solids II: Band TheoryA. Phase changes: Metals have moderate to high melting points because the attractionsbetween the cations and the delocalized electrons are not broken during melting.B. Mechanical properties: When struck by a hammer, metals usually bend or dentrather than crack or shatter. Instead of repelling each other, the metal cations slidepast each other through the electron sea and end up in new positions.C. The lower energy MOs are occupied by the 2s1 valence electrons and make up thevalence band. D. Conductivity: Metals are good electrical conductors because the mobile electronscarry current. Metals conduct heat well because the mobile electrons disperseheat more quickly than do the localized electron pairs or fixed ions in other materials.E. The empty MOs that are higher in energy make up the conduction band.F. Electrical conductivity: Metals conduct so well because an applied field easily excites thehighest energy valence electrons into empty conduction orbitals, allowing them to movethrough the sample. G. Luster: With so many closely spaced levels available, electrons absorb and releasephotons of many frequencies as they move between the valence and conduction bands.H. Malleability : Under an applied force, layers of positive metal ions move past eachother, always protected from mutual repulsions by the delocalized electrons.I. Thermal conductivity: When a metal wire is heated, the highest energy electronsare excited and their extra energy is transferred as kinetic energy along the wire’slength.X. Conductivity of Solids and the Size of the Energy GapA. The conducting properties of a substance are determined by the energy gap between the valence and conduction bands of molecular orbitals (MOs).B. The valence and conduction bands of a conductor have no energy gap between them, soelectrons flow when a tiny electrical potential difference is applied.C. In a semiconductor, a small energy gap exists between the valence and conduction bands.D. In an insulator, a large energy gap exists between the bands: no current is observed even when the substance is heated.E. Another type of electrical conductivity, called superconductivity, has been the focus of intensive research for the past few


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NIU CHEM 211 - Characteristics of Liquids and Structural Features of Solids

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