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IUB CHEM-C 118 - 10-22 chapter 11

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Clicker Question11: Solids and MaterialsTypes of Solids11.6 Crystalline SolidsCrystalline SolidsCubic Unit CellsCubic Unit CellsCubic Unit CellsCubic Unit CellsClosest Packing of SpheresClosest Packing of SpheresClosest Packing of SpheresClosest Packing of SpheresCubic Close PackedWhich packing scheme gives the highest density of spheres?Ionic Crystal StructuresIonic Crystal StructuresIonic Crystal StructuresIonic Crystal StructuresClicker QuestionWhich statement is false?A. Amorphous solids have very little long-range orderB. Metallic solids are good conductors of heat and electricityC. Molecular solids are held together by covalent bonds  molecules have covalent bonds molecular solids aren’t held together by covalent bondsD. Network solids are bonded together into infinite molecules by covalent bonds11: Solids and Materials11.5 Types of Solids11.6 Crystalline Solids11.7 Network Solids11.8 Materials Science11.9 Metals, Semiconductors, and Insulators11.10 Silicon and the Chip11.11 Cement, Ceramics and GlassFriday, October 17, 2014Read: Sections 11.5 for FridaySections 11.6, 11.7 and 11.8 for WednesdayEnd of Chapter 11 Problems: 59, 61, 63, 65, 72, 75, 77, 84, 86, 88, 90, 92, 93, 108Friday, October 17, 2014Read: Sections 11.5 for FridaySections 11.6, 11.7 and 11.8 for WednesdayEnd of Chapter 11 Problems: 59, 61, 63, 65, 72, 75, 77, 84, 86, 88, 90, 92, 93, 108Types of SolidsSolids can be divided into:Crystalline solids•long-range order•sharp melting pointsAmorphous solids•no regular repeating units•melt over a range of T11.6 Crystalline SolidsCrystals have planar faces and sharp angles.The angles are characteristic of the substance.•they don’t depend on crystal size•they reflect the shape of the crystal lattice•Unit cell- smallest part of a lattice that can be used to create full latticeCrystalline Solids2D unit cell example:•The unit cell is a square.•Each corner contributes ¼ of a circle to the unit cell.•Net of 1 circle/unit cell (one circle, but not necessarily in one piece)•The entire lattice can be formed by adding unit cells to each faceCubic Unit CellsCrystals have 3D unit cells. There are 7 types.The simplest are the cubic cells.•Faces meet at 90° with equal-length sides(cube).Cubic cells are divided into 3 sub types:•simple (or primitive) cubic. (sc)•body-centered cubic. •face-centered cubic.Cubic Unit CellsPrimitive (simple) cubic•Atoms sit at the corners of squares.•Layers stack atom-on-atom.•One atom/cell (8 x 1/8).•Atoms occupy 52% of the total volume132456at rearCubic Unit CellsBody-centered cubic•An extra (unshared) atom sits in the center•(8 x 1/8 ) + 1 = 2 atoms/cell•An atom in the diamond gap68 % of the space is occupied.Cubic Unit CellsFace-centered cubic•1 atom at the center of each face.•Face atoms are shared by 2 cells.•(6 x ½ + 8 x 1/8 ) = 4 atoms/cell.74% of the space is filled by atoms- upper limitClosest Packing of SpheresMetal crystals haveequal-sized atoms (spheres).SinglelayerIn closest packing, each atom has 6 neighbors/layerLargest amount in the closet layerClosest Packing of SpheresLayers stack with the atoms in one layer resting in “holes” of another.hexagonal close packingAn abab structureThis is also the fcc structurebut seen from a differentperspectiveLook exactly same- layer and positionababClosest Packing of SpheresStart with “ab”(“b” layer in “a” holes)Add another “a” layer(Green directly over green).Cubic Close Packinghas an abcabc structure(the unit cell is face centered cubic)Closest Packing of SpheresabcaCubic Close PackedStart with “ab”.(“b” layer in “a” holes)Add “c” (gold) above holes in the original green “a” layer.Which packing scheme gives the highest density of spheres?A. Simple cubicB. Hexagonal close packingC. Body centered cubicIonic Crystal StructuresIonic crystal structures are more complex.The ions making up the crystal:•are not identical to each other•may be of very different sizes•may have different number of charges •may not be “spheres” (polyatomic ions...)Ionic Crystal StructuresMany ionic compounds have:•sc or fcc negative-ion lattices (anions are usually larger)Csl = Simple cubic l–•Unit cell: 8 x 1/8 = 1 l– and 1 Cs+Ionic Crystal StructuresNaCl has an fcc Cl– lattice; Na+ in octahedral holes.•Each Na+ is surrounded by 6 Cl–.•Each Cl– is surrounded by 6 Na+.It also contains 4 Na+: •12 edges x ¼ Na+/edge = 3 Na+•1 center x 1 Na+/center = 1 Na+The NaCl unit cell contains 4 Cl– ions:Ionic Crystal Structures•8 corners x 1/8 Cl– / corner = 1 Cl–•6 faces x ½ Cl– / face = 3


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IUB CHEM-C 118 - 10-22 chapter 11

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