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. C.N. Na+ Mg+2 Al+3 Si+4 P+5 S+6 O-2 S-2 [4] [6] XXX [8] XXX 1.42 XXX [12]1.39 XXX CATIONS ANIONS

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

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

Ionization Potential Energy 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

Ionization & Electronegativity + 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) X-RAYS

“NaCl Structure” 2.8 Ang u = (A q 1 q 2 )/r Bond Energy is proportional to product of charges & inverse to bond length Ionic Bond

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

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

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

Mg 1s 2 2s 2 2p 6 3s 2 sp-hybrid GasMetal Lattice Doping GeLi - γ SiLi - x Ionic Solid Conductivity Good - Poor Other Elements Neighbour atoms Excite or promote Electrons σ - bond π - bond

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

C in Diamond, O in Ice, Si 4+ in SiO 2

Bonding Types for Different Minerals NiAs MoS 2 Sb 2 S 3 PbS ZnS CCu Al 2 O 3 NaCl Mg 2 SiO 4 (Ca,Na) 2-3 (Mg,Fe,Al) 5 (Al,Si) 8 O 22 (OH,F) 2 Groups I & VII or II & VI  Electron sharing 

Minerals with more than 1 Bond Type C in (CO 3 ) -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 (CO 3 ) -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