Lecture 02 - Periodic Trends G
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Transcript of Lecture 02 - Periodic Trends G
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Periodic Trends and BondingMCAT Lecture 2G-Chem
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Common Group NamesS block Group I: Alkali metals (reactive to H20) Group II: Alkaline earth metals (insoluble)
D block Transition metals (many oxid. states)
P block Group VII: Halogens Group VIII: Noble Gases (inert)
F block Rare earth metals
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Et CeteraAlkali -extremely reactive -soluble
Alkaline Earth -mostly not soluble (coulombs law)
Transition Metals -various oxidation states
Rare Earth Metals -uranium last natural element
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Et Cetera 27 diatomic elements H2 N2 O2 F2 Cl2 Br2 I2
Pseudo Noble Gas N2
Liquids at 25C Br2 Hg
Colors Cu- blue Cl2 greenish gas Br2 red I2 purple
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MetalsPropertiesLustrous (shiny)Malleable (hammered into sheets)Ductile (wires)Lewis AcidsOxidized (lose e-)6) Delocalized valence electrons -Electrical Conductor -Thermal Conductor
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ZeffZeff = ability of protons to pull electrons toward the nucleus
Function of:Proton numberNumber of shells
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Periodic TrendsShielding vs. Zeff
Across = adds protons ; increases ZeffDown = adds electron shells ; decreases Zeff
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Atomic RadiusRadius increases left ; decreasing ZeffRadius increasess down ; decreasing Zeff
increases
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Ionic RadiusRemove electrons = increase Zeff, reduce repulsionAdd electrons = decrease Zeff, add repulsion
cation radius < neutral radius < anion radius
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ElectronegativityAn atoms ability to pull electrons to itself in a covalent bond
Increases right ; increasing Zeff, close to octetIncreases up ; increasing Zeff
increases
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Electronegativity ApplicationList top 10 electronegative atoms
Dr. F>O>N>Cl>Br>I>C>S P>H.d
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Electron AffinityEnergy involved in putting an electron onto a single atom
+ endergonic (unstable)- exergonic (stable) (-)
(+)Noble gases excepted
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Ionization EnergyEnergy required to remove least tightly bound electron (always +)
Energy increases right ; Zeff increasingEnergy increases up ; Zeff increasing
increases
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I.E. ApplicationPlace the following in order of increasing first ionization energy:Li Be B C N O F Ne
Li B Be* C O N* F Ne
*Exceptions at half and full closed subshells
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AcidityDetermined by strength of bond holding H
increasing
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Formal ChargeAre atoms being shared in the best possible way?
FC = v.e. b.e. l.e.
Use the box method!
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Formal Charge ApplicationDetermine the best lewis diagram for NO using formal charge
Determine formal charges on H2CO3
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HybridizationThe way of best arranging valence electrons in a bonds p p p d d d d d
Rules:Every attachment uses one orbitalLone pairs use one orbital
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VSEPRGeometric Family: lone pairs = bonding pairs
Molecular Shape: lone pairs = bonding pairs
MINIMIZE REPULSION
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Geometric FamiliesOne hybridization = one geometry
# e- groups Hybridization Family 2 sp linear 3 sp2 trigonal planar 4 sp3 tetrahedral 5 sp3d trig. bipyramidal 6 sp3d2 octahedral
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Molecular ShapeIf # lone pairs is zero, geometry = shape
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Molecular Shape 2 Family Possible Shapes linear 0linear trig. planar 1bent tetrahedral 1trigonal pyramidal 2bent trigonal bipyramidal 1seesaw 2t-shape octahedral 1square pyramidal 2square planer
When lp equals zero, GEOMETRY = SHAPE
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Molecular Shape ApplicationDetermine hybridization, geometric family, and molecular shape:H20 sp3, tetrahedral, bentCCL4 sp3, tetrahedral, tetrahedralXeOF4 sp3d2, octahedral, square pyramidHClO4 sp3, tetrahedral, tetrahedralH2CO3 sp2, trigonal planar, trigonal planarBrF3 sp3d, trig. bipyramidal, t-shaped
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VSEPR ApplicationDraw Lewis structures for O2 and O3.
O=O O-O=O
Why does ozone have a higher b.p. than oxygen? -ozone is polar and has dipole-dipole intermolecular forces
Why is ozone more soluble than oxygen? -ozone is polar
Why are the two bonds in ozone equal length and each longer than the bond in diatomic oxygen? -ozone has resonance making for two incomplete double bonds compared to oxygens full double bond
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Intramolecular ForcesNon-polar Covalent: equal sharing of electrons H2 N2 O2 F2 Cl2 Br2 I2
Polar Covalent: unequal sharing of electrons -forms dipole moment HCl, CO, H2O
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Intramolecular Forces 2Coordinate Covalent: donates orbitals and donates electrons Lewis Acid electron acceptor (usually metal or B) Lewis Base electron donor
Metallic: sea of electrons
Network Covalent: all bonds covalent, no distinct molecule, no intermolecular
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Intermolecular ForceIonic: two ions
Ion-Dipole: ion/polar Dipole-Dipole: polar/polar
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Intermolecular Forces 2Dipole-Induced Dipole: polar/non-polar
London: non-polar/non-polar Function of: 1) size 2) # of e-
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London Dispersion Force ApplicationOrder HCl, HBr, and HI in increasing order of boiling pointsHCl < HBr < HI
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H-bondingBoth molecules must have an N, O, or F and one molecule must have an H already attached to its N, O, or F
Roughly 5-10% the strength of a covalent bond
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H-bond applicationWhy cant H2S H-bond (even though it is in the same family as H20)? -S does not pull enough electron density away from H to make H positive enough
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All ForcesListed in order of decreasing strengthCovalentPolar Covalent CovalentCoordinate CovalentIonicIon-DipoleH-bonding ElectrostaticDipole-DipoleDipole-Induced Dipolevan der Waals
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H-bonding ApplicationCan H-bonding occur?CH4 / H2O NoHF / NH3 Yes
Whose H-bonds are stonger?HF / NH3HF / H20 stronger (larger dipole)