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Camosun College GEOS 250 Lectures: 9:30-10:20 M T Th F300 Lab: 9:30-12:20 W F300

Introduction to Mineralogy Dr. Tark Hamilton Chapter 3: Lecture 9 The Chemical Basis of Minerals (sizes, shapes & directions). Camosun College GEOS 250 Lectures: 9:30-10:20 M T Th F300 Lab: 9:30-12:20 W F300. “NaCl Structure”. Ionic Bond. 2.8 Ang. u = (A q 1 q 2 )/r.

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Camosun College GEOS 250 Lectures: 9:30-10:20 M T Th F300 Lab: 9:30-12:20 W F300

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  1. Introduction to MineralogyDr. Tark HamiltonChapter 3: Lecture 9The Chemical Basis of Minerals(sizes, shapes & directions) Camosun College GEOS 250 Lectures: 9:30-10:20 M T Th F300 Lab: 9:30-12:20 W F300

  2. “NaCl Structure” Ionic Bond 2.8 Ang u = (A q1 q2 )/r Bond Energy is proportional to product of charges & inverse to bond length

  3. Electronegativity: atom’s attractionfor electrons in a bond (empirical) Electron Acceptors H – H = 0, pure covalent O – H = 1.4, polar covalent F – Na = 3.1, pure ionic Electron Donors

  4. ΔElectronegativity vs % IonicCharacter, Pauling (1960) CsF CaF IC = 1 – e -0.25(a-b)exp2 KO, BaO TiO AlO, BeO NaCl SiO HO BeO CO ZnS AuTe AsS

  5. Coesite: SiO2 , 2/m, 3Gpa, 700°C 0 Electron Density Distribution: Contour: 0.1 e- /Ang3 + ______ , - ……… Si Si O Si --- O 1.61 Angstroms 0 0 after Geisinger & Gibbs (1983)

  6. Polarization = Van der Waal’s Bonds Nucleus of Neighbour atom attracts electrons Hydrogen Bonding is strongest London Dispersion Forces (weak dipoles) Induced dipole

  7. Cleavage follows Van der Waal’s Bonds 1.42 Angstroms C-C bonds in sheets delocalized & same as Benzene or Diamond Perfect Cleavage Moh’s Hardness = 1

  8. Orthorhombic Sulfur (2/m 2/m 2/m) Sulvere – Sanscrit Sulphurium - Latin S 8 rings Covalent S-S, 2.06 angstroms in rings SSS, 108° bond angle 98° dihedral angle Colour depends on Traces of other polymorphs Van der Waal’s Bonds Hardness ~ 2.0 Melts 112.9°C Volcanic exhalites & Bacterial reduction of (SO4)-2 in sediments • 95.3°C β-Sulfur Monoclinic Rosickyite

  9. Packing Styles of Polar Molecules Dipoles alternate H - bonding Dipole H2O molecule Cubic Ice 1c 4c3

  10. Common Coordination Polyhedra

  11. Limiting Radius Ratios – Coordinating anions contact each other & cation (Pauling’s 1st rule)

  12. What is the Numerical Value of ionic radius?

  13. What's the Numerical Value of a specific Ionic Radius? • Ionic Radii in most scales do not generally meet at experimental electron density minima, because of polarization of the anion by the cation • The various scales are designed to be self-consistent in reproducing ro = r+ + r- • Ionic radii change with coordination number • r8 > r6 > r4 {use the appropriate one!} • Use the same scale for cation and anion

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