CHEM 106 1nd Edition Lecture 1 Outline of Last Lecture I. NOutline of Current Lecture II. Solids III. Metallic bonds and conductivityIV. Structure of metalsa. Layering methodsV. AlloysCurrent LectureChapter 12: Solids12.1 Metallic Bonds + Conduction BondsMetals: malleable, ductile, shiny, conduct heat + electricityBonding: electrons from partially filled orbitalsEx: Cu [Ar] 3d10 4s1 consider only 4s11 electron/Cu enough to make Cu – Cu, but a Cu atom is bonded to 12 nearest neighbors equally Fig 12.1Metallic bonding: involved delocalized (diffuse) electrons (shared among all of the Cu atoms) consistent with low electronegativity and low ionization energyThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Band theory: extension of molecular orbital theory (9.7)*“sea” of valence electronsCu2 2 atomic orbitals combine to make 2 molecular orbitals (w/ 2 valence electrons)# atomic orbitals = # molecular orbitals = # valence electronsFig 12.2Molecular orbitals are spaced very closely in energy, essentially continuousEach Cu supplies 1 electron, each molecular orbital holds 2 electronsBand (valence band) is half filledElectrons move betweenA filled band does not allow conduction, however:Zn [Ar] 3d10 4s2 4p0 Fig. 12.3 4s valence band completely filled 4p conduction band emptyMolecular orbitals from 4p (4p band) overlap the molecular orbitals from 4s (filled 4s band)*Conductivity occurs by promotion of an electron to the empty 4p band12.2 Semiconductors *Skip this section*12.3 Structure of MetalsCrystalline – pure metals Fig. 12.6 (most efficient way to pack balls together)Closest packed layer: 2 ways to stack itA positions 1st layer -next layer can be above a or in the other option cB positions 2nd layerHexagonal closest packed… abab Fig. 12.6, 12.8Cubic closest packed… abcabc Fig. 12.6, 12.11Any closest packed structure gives a packing efficiency of 74% (% of the volume occupied)Less closely packed:Simple cubic Fig. 12.12 52% packing efficiencyBody centered cubic Fig. 12.13 68% packing efficiencyUnit Cells Fig. 12.16Basic (minimum) repeating unit, represents stoichiometry, geometry, density of the entire crystalUnit cell represent by the lines in figures + only the parts of the atoms within the cell Fig. 12.17Corner atom = 1/8 edge atom = ¼ face atom = ½ centered atom = 1*This can be used to determine stoichiometryEx: counting atoms in unit cellsSimple cubic – atoms only at corners 8 corners * 1/8 atom/corner = 1 atomBody centered cubic –8 corners * 1/8 atom/corner + 1 center atom * 1/1 atom/center = 2 atomsEx: atomic radius from cell dimensionsFace centered cubic (cubic closest packed) Fig. 12.18, 12.20Atoms touch along the diagonal Diagonal = 4r = √2 L where L is the length of the unit cellTherefore r=√24∗LL is measured by x-ray crystallography12.4 AlloysMixtures of metals (or a metal with a smaller amount of a non-metal)Homogenous alloys – substitutionalBronze Cu + SnSn atoms replace up to 30% of the Cu atomsCu and Sn have similar radii + the same crystal structuresInterstitial – atoms added in the holes in the pure metal crystalFig. 12.26 holes in a closes packed latticeTetrahedral holes: 4 atoms around the holes4 host atoms around hole in which non-host (alloy) atom can fitOctahedral holes: 6 host atoms around the