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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 8 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. Effective Ionic Radii in Minerals I.R. increases with C.N.

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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 8The 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. Effective Ionic Radii in MineralsI.R. increases with C.N.

  3. Cation Size Increases With C.N. 3 Trigonal Planar 4 Tetrahedral 6 Octahedral 8 Cubic 12 Dodecahedral C+4, N+5

  4. Polarization Distorts Electrons Get a load of that tight little cation!

  5. Ionization PotentialEnergy added to an atom to remove an electron • X atom – e- X+cation • Atom gains energy: ΔEnergy > 0 • X atom + e- X-anion • Atom loses energy: ΔEnergy < 0 • Unpaired electrons are most easily removed

  6. Ionization & Electronegativity X-RAYS + ΔE added to lone gaseous atom to remove 1 electron eV or kJoules/mol Atom’s tendancy to attract electrons to itself in bonds (Pauling, qualitative)

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

  8. “Wife Swapping – Melting” Linear Na Halides & Anion size Alkaline Earth Oxides vs Cation Size Parabolic 1.02 Alkali Fluorides vs Cation Size 1.38 0.74 F’s repel 1.52

  9. “Wife swapping – Hardness” Alkaline Earth Oxides vs Hardness Bond length & Strength vs Hardness mp 2700° mp 990°

  10. Conduction Band Electrons: Metals Conductivity Possible electron path + nuclei Conduction band electrons In metals, electrons are Higher in energy than the valence bands, e.g. promoted by adjacent atoms after R.T. Downs Univ. Arizona +Cu Atom

  11. Neighbour atoms Excite or promote Electrons Mg 1s2 2s2 2p6 3s2 Gas Metal Other Elements sp-hybrid π - bond σ - bond Lattice Doping GeLi - γ SiLi - x Ionic Solid Conductivity Good - Poor

  12. Electron Probability Distribution Covalently Bonded Atoms or Ions Lewis Dot Structure, :N:::N: Stable Inert Gas Configuration H-H, Cl-Cl, H-Cl O=O, (S=S)-2 Hg-Hg, Au-Au σ – bond or sp – bond Like Z or Unlike Z VSEPR Theory

  13. C in Diamond, O in Ice, Si4+ in SiO2

  14. Bonding Types for Different Minerals Al2O3 Groups I & VII or II & VI NaCl Mg2SiO4 (Ca,Na)2-3(Mg,Fe,Al)5(Al,Si)8O22(OH,F)2 ZnS PbS Electron sharing  Sb2S3 C Cu NiAs MoS2

  15. Minerals with more than 1 Bond Type • C in (CO3)-2 is covalent bonded to Oxygen • Δe.n. 3.5 – 2.5 = 1.0 • If +4 it would have an Ionic Radius of -0.08Ang • Thus it is held tighter than the ion in [3] Coordination • Ca+2 in Calcite is bonded to O-2 in (CO3)-2 • Δe.n. 3.5 – 1.1 = 2.4 thus ionic • Cleavage must cut pairs of ions, not between • This goes for salts of most oxyanions

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