D:\352\2009\LectureNotes\Part1Chemistry.wpdEPSc 352: Lecture Overview for Part 1, Mineral ChemistryFill out questionnaires: please print Hand-outs: syllabus, homework set #1; first lab to come by e-mailGoals of the CourseWalk through syllabus: schedule, expectations(( Assignment: Begin reading chapters 1 and 3 in your text. NOTE: Thedesignation “K&D” refers to your textbook, Klein and Dutrow (2008) Mineral Science.Page 9, Fig. 1.9: 5 major aspects of “mineral science”Definition of a mineral: properties and examples of their implicationsWays of classifying minerals: according to one’s use of minerals; by analogy with chemicalcompoundsMineral definition “challenged” by the notion of biominerals**Each mineral is defined as a combination of a structure and a composition: examplesBegin the course by investigating compositional/chemical aspects of mineralsBulk composition (define) of the earth (especially the crust) is our starting (and ending) pointFundamental observations: Earth is not homogeneous in composition or structureMany types of minerals (not infinite #); distributed differently throughout earthLayered structure of the earth, each layer with a different average composition and bulkgeophysical properties, e.g., transmission of seismic wavesCompositions of existing minerals reflect the bulk chemical reservoir and the ways in whichelements distribute themselves among various (competing) species.Chemical affinities: chalcophile, lithophile, siderophileAverage abundance vs. local concentrationWalk through the geochemical hand-outs #1-4 on crustal averages.Hand-outs #5-7: 98.5 wt.% of earth’s crust from only 8 elements, O, Si, Al, K, Na, Fe, Mg, CaHand-out #3 describes major, minor, trace, and dispersed elementsElement distribution is governed by (geo)chemical lawsHow do we get a whole ore deposit of a geochemically minor/trace element like Au?Element partitioning (choice): crystal chemistryEfficiency in separating and concentrating elements2Minerals as repositories for and reservoirs of the elementsMineral must reach saturation in order to form, i.e., create a compound rather than remain asdispersed elements.How much concentration over crustal average concentration is required for saturation?Elements that form own mineral vs. those that “hop a ride” in solid solutionCrystal chemistry: relation between mineral’s composition, structure, and chemical & physicalproperties, including optical properties under the microscope.K Review (romp through!) atomic structure and electronic configuration.Importance of atomic/ionic size and charge (electronic structure) in stabilization of minerals.Atomic radii: actual radii (0.46 - 2.62 Å) vs. effective radii (# and type of neighbors, ion charge)Impetus for chemical reactions (including mineral formation): attain lowest possible energy stateHand-outs 8-10: orbital structure, aufbau principle, electronic configurations.Valence electrons are those in the highest-energy orbitals; gained or lost in reactionPrinciples of lowest energyTransition elements: oxidation states, color in mineralsValence electrons (in the highest-energy orbitals): those that participate in reactionsStructure of the periodic tableElements in same column have same # electrons in valence shell, so chemically similarRegular pattern to atomic/ionic radii down same column and across same rowK Nature of Chemical Bonds5 types of bonds (3 of them involving valence electrons):Type of bond: 1) is determined by electronic properties of participating atoms, 2) controls chemical and physical properties of compound (see K&D Table 3.10 on p.56), 3) is “gradational” (% ionic character, etc.); see K&D Fig. 3.19 on p. 60Driving force for bonding: achieve stable electronic configuration (mimic noble gases); Table3.6 on pp. 44-45 shows electron configurations of the neutral elementsCan predict compound formation/stabilization and bond strength through knowledge of specific energetic and electronic tendencies of the atoms: electronegativity – see K&D Fig. 3.22 on p. 60 ionization potential (Table 3.5 on p. 43)3 electron affinity (inverse of ionization potential)In ionically bonded compounds, those with greatest )electronegativities have strongest bonds.Second important factor in atomic interactions is atomic/ionic radii.Effective radius (1/2 distance between 2 nuclei) depends on (distortions of) electron clouds ofatoms/ions; radius changes as function of # of nearest neighbors, theirelectronegativities, and their charges.5 types of bonds: simply are models for characteristics of bondingRemember: Driving force for bonding is to achieve stable electronic configuration (mimic noblegases)Basic models of bonding are ionic: geometric, fitting together of spheres of different sizes (next week’s lab)covalent: nature & shape of atomic orbitals with unpaired electrons; orbitals overlapTogether with metallic bonding, these 3 types involve valence electrons.Ionic bonding model: ions are simple spheres (with a size/radius and a charge)“Lose” or “gain” electrons to mimic noble-gas configurationNon-directional bonding: high symmetryShorter the bond length, stronger the bond (imparts properties; K&D pp. 54-55)Higher the charges on the ions, stronger the bond (shorter the length)If )electroneg. $ 2.0 (from Pauling’s data), bonding is ionic (see K&D, p. 61, Fig. 3.21)Covalent bonding model: electron sharingOccurs among atoms with high but similar electronegativitiesPolarized electron cloud produces highly directional bondsLower symmetry than ionic bonds. (Many ionic compounds are cubic, e.g., NaCl)Elements in columns IIIa, IVa, Va,VIa have several valence electrons, permitting multiplebonds & atomic clusters, e.g., CO32-, SO42-, SiO44-: Trigonal planar, tetrahedral atomicarrangements.% of bonding type: greater the )electroneg., more ionic in character. Silicate minerals havestrong covalent and ionic character (K&D, p. 60, Fig. 3.19 and p. 61, Fig. 3.21).Metallic bond: electrons de-localized. Luster, electrical conductivity. Low but similar electroneg.Bonds that do not involve valence electrons:van der Waals bonds: weakest type, but still significant.Force develops between electrically neutral clusters (molecules) due to slightimbalances in electron distribution (“residual charges”)Observed in organic compounds, graphite (between planes)Hydrogen bonds: second weakest type. Develop if H is bonded to a strongly electronegative4element (which