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UNC-Chapel Hill CHEM 251 - Exam 1 Study Guide

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CHEM 251 1nd EditionExam # 1 Study Guide Lectures: 1 - 12Lecture 1 (January 8)Periodic Trends: across a period-similar orbital structure, down a group-similar propertiesPhysical Properties:Metals: often exhibit ductility (stretchable) or malleability (squishable), highly conductive in three dimensionsWeak metals: A little bit less metallicSemi-metals: Even less metallic — these tend to form small molecules rather than metallic sheetsNon-metals: These are clearly not metals — non-conducting, often liquids or gases.Lecture 2 (January 10) Periodic Trends (continued):Stability-elements above lead unstable, magic numbers-2, 8, 20, 28, 50, 82, 126, even atomic #s more abundant, heavier elements less abundantAtomic radius-decreases going up and rightIonization energy-increases going up and rightElectron affinity-increases going up and rightLecture 3 (January 13) Orbital Structure energy ordering:Orbital shapes: s, p, and dS: non-zero probability of finding electron inside the nucleusP: Each p-orbital has one node, 3 equivalent orbitalsD: 2 nodes, 5 equivalent orbitalsLecture 4 (January 15) Effective Nuclear Charge-how much of the positive charge is felt by each electronIncreases across period, remains fairly constant down a groupSlater’s Rules-given on testNuclear Chemistry238U is most stable, 235U is most commonLecture 5 (January 17) Problem Session-filling in periodic table, identifying trends, calculating effective nuclear chargeLecture 6 (January 27) Lewis Dot Structures-ensure an octet, minimize overall charge, avoid adjacent charges, resonanceMolecular OrbitalsBond order = total # of bonding orbitals – total # of anti-bonding orbitalsLecture 7 (January 31) MixingOccurs in CO2 because C 2s close in energy to O 2pVSEPR TheoryPredict molecular geometry (affected by lone pairs)Lecture 8 (February 3) Problem Session-atomic orbital overlapLecture 9 (February 5) Symmetry: language used to describe the readily apparent symmetry in molecular geometrySymmetry operations: action that leaves the molecule in a form indistinguishable from the original Symmetry elements: point, line, or plane around which symmetry operations are performedPoint groups: unique label that describes all symmetry elements of a moleculeSymmetry OperationsIdentity (E)-Do nothingProper Rotation (Cn where n=360/degrees of rotation)-Rotate the moleculeReflection (σ)-Reflect the molecule across a planeInversion (i)-Reflect the molecule through a pointImproper Rotation (S)-Rotation about an axis followed by reflection across a planeLecture 10 (February 7) Applications of SymmetrySpectroscopy: Molecular symmetry determines # vibrations observed by IR or Raman spec, IR spec does not detect totally symmetric vibrations, Greenhouse gases like CO2 absorb IR and trapit in atmospherePolarity: Highly symmetric molecules have no dipole moment, Lower symmetry molecules tend to be less polarChirality: Cn and Dn point groups always chiral (no mirror plane), But C2v / C2h etc. achiralLecture 11 February 10) Metals3-D electrical conductivity at SATPConductive, reflective, shiny, malleable or ductile, high melting pointsConductive metals can easily access antibonding orbitalsBonding occurs through s orbitals so angles are not important-Explains ductility or malleabilityBand GapDopingB-doped (p-type): accepts electronsP-doped (n-type): donates electrons Lecture 12 (February 12) Metal StructureSimple Cubic, body centered, hexagonal close packing, face-centered/cubic close packing2 types of alloysbulk => nanoparticles = quantum


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