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Crystal Chemistrychemistry Crystalcrystal Chemistrychemistry OreOre MineralogyMineralogy (EMR(EMR 331)331) CrystalCrystal chemistrychemistry CrystalCrystal ChemistryChemistry PartPart 1:1: Atoms,Atoms, ElementsElements andand IonsIons WhatWhat isis CrystalCrystal Chemistry?Chemistry? studystudy ofof thethe atomicatomic structure,structure, physicalphysical properties,properties, andand chemicalchemical compositioncomposition ofof crystallinecrystalline materialmaterial basicallybasically inorganicinorganic chemistrychemistry ofof solidssolids thethe structurestructure andand chemicalchemical propertiesproperties ofof thethe atomatom andand elementselements areare atat thethe corecore ofof crystalcrystal chemistrychemistry therethere areare onlyonly aa handfulhandful ofof elementselements thatthat makemake upup mostmost ofof thethe rockrock --formingforming mineralsminerals ofof thethe earthearth ChemicalChemical LayersLayers ofof thethe EarthEarth SiO2 – 45% MgO – 37% FeO – 8% Al2O3 – 4% CaO – 3% others – 3% Fe – 86% S – 10% Ni – 4% CompositionComposition ofof thethe EarthEarth ’’ss CrustCrust AverageAverage compositioncomposition ofof thethe EarthEarth ’’ss CrustCrust (by(by weight,weight, elements,elements, andand volume)volume) TheThe AtomAtom The Bohr Model The Schrodinger Model Nucleus - contains most of the weight (mass) of the atom - composed of positively charge particles (protons) and neutrally charged particles (neutrons) Electron Shell - insignificant mass - occupies space around the nucleus defining atomic radius - controls chemical bonding behavior of atoms ElementsElements andand IsotopesIsotopes Elements are defined by the number of protons in the nucleus (atomic number). In a stable element (non -ionized), the number of electrons is equal to the number of protons Isotopes of a particular element are defined by the total number of neutrons in addition to the number of protons in the nucleus (isotopic number). Various elements can have multiple (2-38) stable isotopes, some of which are unstable (radioactive) Isotopes of a particular element have the same chemical properties, but different masses. Isotopes of Titanium (Z=22) Isotope Half-life Spin Parity Decay Mode(s) or Abundance 38Ti 0+ 39Ti 26 ms (3/2+) EC=100, ECP+EC2P ~ 14 40Ti 50 ms 0+ EC+B+=100 41Ti 80 ms 3/2+ EC+B+=100, ECP ~ 100 42Ti 199 ms 0+ EC+B+=100 43Ti 509 ms 7/2- EC+B+=100 44Ti 63 y 0+ EC=100 45Ti 184.8 m 7/2- EC+B+=100 46Ti stable 0+ Abundance=8.0 1 47Ti stable 5/2- Abundance=7.3 1 48Ti stable 0+ Abundance=73.8 1 49Ti stable 7/2- Abundance=5.5 1 50Ti stable 0+ Abundance=5.4 1 51Ti 5.76 m 3/2- B-=100 52Ti 1.7 m 0+ B-=100 53Ti 32.7 s (3/2)- B-=100 54Ti 0+ 55Ti 320 ms (3/2-) B-=100 56Ti 160 ms 0+ B-=100, B-N=0.06 sys 57Ti 180 ms (5/2-) B-=100, B-N=0.04 sys 58Ti 0+ 59Ti (5/2-) B-=? 60Ti 0+ B-=? 61Ti (1/2-) B-=?, B-N=? Source: R.B. Firestone UC-Berkeley StructureStructure ofof thethe PeriodicPeriodic TableTable # of Electrons in Outermost Shell Noble Gases Anions --------------------Transition Metals------------------ Primary Shell being filled Ions,Ions, IonizationIonization Potential,Potential, andand ValenceValence StatesStates Cations – elements prone to give up one or more electrons from their outer shells; typically a metal element Anions – elements prone to accept one or more electrons to their outer shells; always a non -metal element Ionization Potential – measure of the energy necessary to strip an element of its outermost electron Electronegativity – measure strength with which a nucleus attracts electrons to its outer shell Valence State (or oxidation state) – the common ionic configuration(s ) of a particular element determined by how many electrons are typically stripped or added to an ion 1st Ionization Potential Anions Cations Elements with a single outer s orbital electron Electronegativity ValenceValence StatesStates ofof IonsIons commoncommon toto RockRock --formingforming MineralsMinerals Cations – generally +1 +2 relates to column +3 +4 +5 +6 +7 in the periodic table; most -2 -1 transition metals have a +2 -----------------Transition Metals--------------- valence state for transition metals, relates to having two electrons in outer Anions – relates electrons needed to completely fill outer shell Anionic Groups – tightly bound ionic complexes with net negative charge CrystalCrystal ChemistryChemistry PartPart 2:2: BondingBonding andand IonicIonic RadiiRadii ChemicalChemical BondingBonding inin MineralsMinerals BondingBonding forcesforces areare electricalelectrical inin naturenature (related(related toto chargedcharged particles)particles) BondBond strengthstrength controlscontrols mostmost physicalphysical andand chemicalchemical propertiesproperties ofof mineralsminerals (in(in general,general, thethe strongerstronger thethe bond,bond, thethe harderharder thethe crystal,crystal, higherhigher thethe meltingmelting point,point, andand thethe lowerlower thethe coefficientcoefficient ofof thermalthermal expansion)expansion) FiveFive generalgeneral typestypes bondingbonding types:types: IonicIonic CovalentCovalent MetallicMetallic vanvan derder WaalsWaals HydrogenHydrogen CommonlyCommonly differentdifferent bondbond typestypes occuroccur inin thethe samesame mineralmineral IonicIonic BondingBonding CommonCommon betweenbetween elementselements thatthat will...will... 1) easilyeasily exchangeexchange electronselectrons soso asas toto stabilizestabilize theirtheir outerouter shellsshells (i.e.(i.e. becomebecome moremore inertinert gasgas --like)like) 2) createcreate anan electronicallyelectronically neutralneutral bondbond betweenbetween cationscations andand anionsanions Example:Example: NaClNaCl Na (1s22s22p63s1) –> Na +(1s22s22p6) + e - Cl (1s22s22p63s23p5) + e - –> Cl - (1s22s22p63s23p6) PropertiesProperties ofof IonicIonic BondsBonds ResultsResults inin mineralsminerals displayingdisplaying moderatemoderate degreesdegrees ofof hardnesshardness andand specificspecific gravity,gravity, moderatelymoderately highhigh meltingmelting points,points, highhigh degreesdegrees ofof symmetry,symmetry, andand areare poorpoor conductorsconductors ofof heatheat (due(due toto ionicionic stability)stability) StrengthStrength ofof ionicionic bondsbonds areare related:related: 1)1) thethe spacingspacing betweenbetween ionsions 2)2) thethe chargecharge ofof thethe ionsions CovalentCovalent BondingBonding formed by sharing of outer shell electrons strongest of all chemical bonds produces minerals that are insoluble, high melting points, hard, nonconductive (due to localization of electrons), have low symmetry (due to directional bonding). common among elements with high numbers of vacancies in the outer shell (e.g. C, Si , Al, S) Diamond TendenciesTendencies forfor IonicIonic vs.vs. CovalentCovalent PairingPairing Ionic Pairs Covalent Pairs MetallicMetallic BondingBonding atomicatomic nucleinuclei andand innerinner filledfilled electronelectron shellsshells inin aa ““seasea ”” ofof electronselectrons mademade upup ofof unboundunbound valencevalence electronselectrons YieldsYields mineralsminerals withwith mineralsminerals thatthat areare soft,soft, ductile/malleable,ductile/malleable, highlyhighly conductiveconductive (due(due toto easilyeasily mobilemobile electrons).electrons). NonNon --directionaldirectional bondingbonding producesproduces highhigh symmetrysymmetry vanvan derder WaalsWaals (Residual)(Residual) BondingBonding createdcreated byby weakweak bondingbonding ofof oppositelyoppositely dipolarizeddipolarized electronelectron cloudsclouds commonlycommonly occursoccurs aroundaround covalentlycovalently bondedbonded elementselements producesproduces solidssolids thatthat areare soft,soft, veryvery poorpoor conductors,conductors, havehave lowlow meltingmelting points,points, lowlow symmetrysymmetry crystalscrystals HydrogenHydrogen BondingBonding ElectrostaticElectrostatic H+ bondingbonding betweenbetween anan H+H+ ionion withwith anan anionanion Close packing of Anions oror anionicanionic complexcomplex polarized molecules oror withwith aa polarizedpolarized moleculesmolecules WeakerWeaker thanthan ionicionic oror covalent;covalent; stronger than van polarized H 2O stronger than van Ice derder WaalsWaals molecule SummarySummary ofof BondingBonding CharacteristicsCharacteristics MultipleMultiple BondingBonding inin MineralsMinerals Graphite – covalently bonded sheets of C loosely bound by van der Waals bonds. Mica – strongly bonded silica tetrahedra sheets (mixed covalent and ionic) bound by weak ionic and hydrogen bonds Cleavage planes commonly correlate to planes of weak ionic bonding in an otherwise tightly bound atomic structure AtomicAtomic RadiiRadii Absolute radius of an atom based on location of the maximum density of outermost electron shell Effective radius dependent on the charge, type, size, and number of neighboring atoms/ions - in bonds between identical atoms, this is half the interatomic distance - in bonds between different ions, the distance between the ions is controlled by the attractive and repulsive force between the two ions and their charges F = k [(q +)(q -)/d 2] Coulomb ’s law Control of CN (# of nearest neighbors) on ionic radius Reflects expansion of cations into larger “pore spaces” between anion neighbors CrystalCrystal ChemistryChemistry PartPart 3:3: CoordinationCoordination ofof IonsIons PaulingPauling ’’ss RulesRules CrystalCrystal StructuresStructures CoordinationCoordination ofof IonsIons ForFor mineralsminerals formedformed largelylargely byby ionicionic bonding,bonding, thethe ionion geometrygeometry cancan bebe simplysimply consideredconsidered
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