Lecture 02 - Periodic Trends G

Periodic Trends and BondingMCAT Lecture 2G-Chem

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

Et CeteraAlkali -extremely reactive -soluble

Alkaline Earth -mostly not soluble (coulombs law)

Transition Metals -various oxidation states

Rare Earth Metals -uranium last natural element

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

MetalsPropertiesLustrous (shiny)Malleable (hammered into sheets)Ductile (wires)Lewis AcidsOxidized (lose e-)6) Delocalized valence electrons -Electrical Conductor -Thermal Conductor

ZeffZeff = ability of protons to pull electrons toward the nucleus

Function of:Proton numberNumber of shells

Periodic TrendsShielding vs. Zeff

Across = adds protons ; increases ZeffDown = adds electron shells ; decreases Zeff

Atomic RadiusRadius increases left ; decreasing ZeffRadius increasess down ; decreasing Zeff

increases

Ionic RadiusRemove electrons = increase Zeff, reduce repulsionAdd electrons = decrease Zeff, add repulsion

cation radius < neutral radius < anion radius

ElectronegativityAn atoms ability to pull electrons to itself in a covalent bond

Increases right ; increasing Zeff, close to octetIncreases up ; increasing Zeff

increases

Electronegativity ApplicationList top 10 electronegative atoms

Dr. F>O>N>Cl>Br>I>C>S P>H.d

Electron AffinityEnergy involved in putting an electron onto a single atom

+ endergonic (unstable)- exergonic (stable) (-)

(+)Noble gases excepted

Ionization EnergyEnergy required to remove least tightly bound electron (always +)

Energy increases right ; Zeff increasingEnergy increases up ; Zeff increasing

increases

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

AcidityDetermined by strength of bond holding H

increasing

Formal ChargeAre atoms being shared in the best possible way?

FC = v.e. b.e. l.e.

Use the box method!

Formal Charge ApplicationDetermine the best lewis diagram for NO using formal charge

Determine formal charges on H2CO3

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

VSEPRGeometric Family: lone pairs = bonding pairs

Molecular Shape: lone pairs = bonding pairs

MINIMIZE REPULSION

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

Molecular ShapeIf # lone pairs is zero, geometry = shape

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

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

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

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

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

Intermolecular ForceIonic: two ions

Ion-Dipole: ion/polar Dipole-Dipole: polar/polar

Intermolecular Forces 2Dipole-Induced Dipole: polar/non-polar

London: non-polar/non-polar Function of: 1) size 2) # of e-

London Dispersion Force ApplicationOrder HCl, HBr, and HI in increasing order of boiling pointsHCl < HBr < HI

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

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

All ForcesListed in order of decreasing strengthCovalentPolar Covalent CovalentCoordinate CovalentIonicIon-DipoleH-bonding ElectrostaticDipole-DipoleDipole-Induced Dipolevan der Waals

H-bonding ApplicationCan H-bonding occur?CH4 / H2O NoHF / NH3 Yes

Whose H-bonds are stonger?HF / NH3HF / H20 stronger (larger dipole)