CHEM 123 notes assignments

CHEM 123 notes assignments - Crystal Structure Solids are...

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Chapt. 13 1 Crystal Structure Solids are divided into two categories : Crystalline: Possesses rigid and long-range order. Amorphous: Lacks well-defined arrangement. Structure of a crystalline solid is based on the unit cell, a basic repeating structural unit Classification by Bonding Ionic e.g. NaCl, NH 4 Cl etc Positive and negative ions held in their lattice positions by strong ionic bonds Covalent e.g. diamond, SiO 2 Atoms held in lattice positions by strong covalent bonds Molecular e.g. H 2 O(s), CO 2 (s) Molecules held together by weak intermolecular forces Metallic e.g. Al(s), Fe(s) etc Metal cations held in lattice positions by strong metalic bonds
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Chapt. 13 2 Orthorhombic Monoclinic ZrO 2 Cubic Classification Crystalline Solids Simple Body- centered Face- centered Trigonal Body- centered Simple Rhombohedral Hexagonal Simple Base- centered Body- centered Face- centered Simple Base- centered Triclinic Turquoise, birthstone for December, Sky blue to bluish green. The name means "Turkish stone". Turquoise is porous, so contact with liquids, oils or even perspiration should be avoided. Jewelry made with turquoise should be removed before washing hands, etc. . The pure blue color is rare, most stones contain the matrix from which it was found. Although the stones without matrix are rarer and more valuable, many people find the black matrix attractive, and makes the stone unique. Hardness: 5 - 6 Specific Gravity: 2.6 - 2.8 Chemical Composition: CuAl 6 (PO 4 ) 4 (OH) 8 *5(H 2 O), Hydrated Copper Aluminum Phosphate Crystal Structure: Triclinic LiSb 2 AsS KNa 22 (SO 4 ) 9 (CO 3 ) 2 Cl Hanksite Sulfur MnCO 3 Rhodochrosite Calcite CaCO 3 (has many Structures) Pyrite FeS 2
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Chapt. 13 3 A three dimensional array of points designating the centers of the components (Such as atoms, ions or molecules ) that shows the repeating pattern of the crystal Lattice Can you pick out the simplest unit cell? Called the Unit Cell
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Chapt. 13 4 Unit Cell It is the smallest unit that, when stacked together repeatedly without any gaps can reproduce the entire crystal. The previous slide showed an example of the simple cubic unit cell. Simple primitive cube Eight equivalent points at the corners of a cube Body Centered Cubic Eight equivalent points at the corners of a cube and one at the centre Another possibility Another possibility Face Centered Cubic Eight equivalent points at the corners of a cube and six on the centre of the cube faces
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Chapt. 13 5 SCATTERING OF X-RAYS BY CRYSTALS ∙ In 19th century crystals were identified by their shape ∙ Crystallographers did not know atomic positions within the crystal ∙ In 1895 Roentgen discovered X-rays ∙ And Max von Laue suggested that crystal might act as a diffraction grating for the X- rays. In 1912 Knipping observed X-Ray Diffraction Pattern ∙ Von Laue gets Noble Prize ∙ Braggs also demonstrated diffraction and formulated a diffraction law. When electromagnetic radiation passes through matter it interacts with the electrons and is scattered in all directions and the waves interfere.
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CHEM 123 notes assignments - Crystal Structure Solids are...

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