Radius_Determination_F11

Radius_Determination_F11 - Si radius = 0.117nm Si C = 0.194...

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1 Radius Determination GLY 4200 Fall, 2011
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2 X-ray Diffraction Image Images like these can be used to determine crystal structures
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3 Comparison of Radii
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4 Squashed versus Unsquashed Left, metallic or covalent radius Rght, Van der Waals radius
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5 Radii Across a Row Diagram uses metallic radii for metallic elements, covalent radii for elements that form covalent bonds, and van der Waals radii for those (like the noble gases) which don't form bonds
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6 Coulomb’s Law • F (Z 1 Z 2 )/r 2 where Z i = charge on each ion r = distance between ions
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7 Covalent Radius Example Example: C-C spacing in diamond is 0.154nm Metallic Si-Si spacing is 0.234nm C radius = 0.077nm
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Unformatted text preview: Si radius = 0.117nm Si C = 0.194 nm predicted 0.193 nm observed 8 Electron Density Contour Map of LiF Electron density (electrons/volume) is the preferred method of determining ionic radius 9 Electron Density Variation Electron density variation between Li + and F- Note the variation has a very flat bottom. M, G and P indicate the true minimum, and the Goldshmidt and Pauling ionic radii 10 Ionic Radii versus CN 11 Ionic Character Example: CaF Ca = 1.1 F = 4.1 Difference = 3.0 Close to 90% ionic Example: SiN Si = 1.8 N = 3.1 Difference = 1.3 28% ionic...
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Radius_Determination_F11 - Si radius = 0.117nm Si C = 0.194...

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