What’s coming up??? Oct 25The atmosphere, part 1Ch. 8 Oct 27Midterm … No lecture Oct 29The atmosphere, part 2Ch. 8 Nov 1Light, blackbodies, BohrCh. 9 Nov 3,5Postulates of QM, p-in-a-boxCh. 9 Nov 8,10Hydrogen and multi – e atoms Ch. 9 Nov 12Multi-electron atomsCh.9,10 Nov 15Periodic propertiesCh. 10 Nov 17Periodic propertiesCh. 10 Nov 19Valence-bond; Lewis structures Ch. 11 Nov 22VSEPRCh. 11 Nov 24Hybrid orbitals; VSEPRCh. 11, 12 Nov 26MO theoryCh. 12 Nov 29MO theoryCh. 12 Dec 1bonding wrapupCh. 11,12 Dec 2Review for exam

COMBINING ORBITALS TO FORM HYBRIDS HYBRIDIZATION : the combination of two or more “native” atomic orbitals on an atom to produce “hybrid” orbitals RULE: the number of atomic orbitals that are combined must equal the number which are formed All resulting hybrid orbitals are identical.

Note that these are +ive on one side of origin and -ive on the other!

Combine one s and one pa sp- hybrid + + ADD the orbitals  2s +  2p HYBRIDIZATION

+ +  2s +  2p The positive part adds to positive part CONSTRUCTIVE INTERFERENCE The positive part cancels negative part DESTRUCTIVE INTERFERENCE

Combine one s and one p to givean sp- hybrid + REMEMBER IF WE MIX TWO WE MUST GET TWO BACK The other combination is s - p  2s +  2p

+ +  2s -  2p The positive part cancels negative part The positive part adds to positive part CONSTRUCTIVE INTERFERENCE DESTRUCTIVE INTERFERENCE

+ We get two equivalent sp orbitals ORIENTED AT  2s -  2p

sp-HYBRIDIZATION The s and p orbitals The two sp-hybrids Directed at 180 0

COMBINE one s-orbital and two p-orbitals Get three sp 2 - orbitals oriented at The s and p orbitals The three sp 2 -hybrids Directed at 120 0

COMBINE one s-orbital and three p-orbitals Get three sp 3 - orbitals oriented at Back to methane

four hybrid orbitals needed to form four bonds s + p x + p y + p z An atom with sp 3 hybrid orbitals is said to be 4 sp 3 hybrids The four sp 3 hybrid orbitals form a tetrahedral arrangement. METHANE: CH 4 sp 3 hybridized C H H H H

E 2p 2s2s Orbitals in free C atom E sp 3 Hybridized orbitals of C atom in methane When orbitals are hybridized they have the same energy: sp 3 hybridization……. The FOUR sp 3 hybrids are DEGENERATE. HYBRIDIZE

C sp 3 HYBRIDS Now form the bonds to the H-atoms……... sp 3 orbitals

C Each bond in methane results from the overlap of a hydrogen 1s orbital and a carbon sp 3 orbital. H H H H Hydrogen 1s orbital Carbon sp 3 orbitals Form a chemical bond by sharing a pair of electrons.  bonds

VALENCE BOND MODEL Step 1:Draw the Lewis structure(s) Step 2:Determine the geometry of the electron pairs around each atom using VSEPR picture of molecular shapes Step 3:Specify the hybrid orbitals needed to accommodate the electron pairs on each atom Hybrid orbital model

AMMONIA: NH 3 N Electron pair geometry is tetrahedral Need sp 3 hybrids H H H

N sp 3 hybrids on N in AMMONIA HHH

Overlap of two of oxygen sp 3 hybrids with ….. H atom 1s orbitals. WATER Lone pairs in two of the sp 3 hybrids. To form two  bonds. Think about H 3 O + !!! O H H

H + ion: empty 1s orbitals. HYDRONIUM ION. O H H H+H+ ISOELECTRONIC WITH …..? NH 3

Ethylene: C 2 H 4 CC H H H H The CARBON is sp 2 hybridized 3 sp 2 hybrids s + p x + p y three hybrid orbitals on each carbon for the trigonal planar electron pair geometry The 3 sp 2 hybrid orbitals form a trigonal planar arrangement. 3 effective electron pairs sp 2 hybridization VSEPR trigonal planar electron pair geometry around each C-atom. a HCH angle of

GROUND STATE C atom E 2p 2s2s sp 2 hybridized orbitals of C FORMATION OF sp 2 hybrids E sp 2 2p HYBRIDIZE This leaves one p orbital unhybrized…….

x y z The unhybridized p orbital is perpendicular to sp 2 plane. sp 2 - hybrid orbitals UNHYBRIDIZED p- orbital An sp 2 hydridized C atom

x y z x y z OVERLAP the sp 2 hybrids from the two carbons to form a sigma bond between them. C C BONDING IN ETHYLENE  bond CC H H H H

x y z x y z The two unhybridized p orbitals are left over to form a ….. H H H H pi bond (  bond)

H H H H CC

 H(1s)-C(sp)  :C(sp)-C(sp)  C(2p)-C(2p) TWO OF THESE!!  H(1s)-C(sp) BONDING SCHEME IN ETHYNE CC H H What does this look like????

x y z x y z OVERLAP the C sp hybrids with H 1s to form sigma bonds HH C C

x y z x y z C C HH two pi bonds (  bonds) LATERAL OVERLAP of p orbitals to form pi bonds.

What about molecules with more than an octet around the central atom? Examples: PCl 5, or SF 4 or SiF 6 2- etc….. Four pairs needs Four orbitals Five pairs needs Five orbitals six pairs needssix orbitals So??????

PCl 5 Cl P We ignore the chlorine atoms and just describe central atom. Need five hybrid orbitals on the phosphorus d + s + p x + p y + p z 5 effective electron pairs dsp 3 hybridization 5 dsp 3 hybrids to fit the trigonal bipyramidal electron pair geometry Five equivalent orbitals……..

dsp 3 - hybrid orbitals x y z TRIGONAL BIPYRAMID overlap with orbitals on chlorine to form 5  bonds

SF 6 F S F F F F F We need six hybrid orbitals on the sulfur 6 d 2 sp 3 hybrids d 2 sp 3 hybridization d + d + s + p x + p y + p z 6 effective electron pairs SIX equivalent orbitals…….. We ignore the chlorine atoms and just describe central atom.

overlap with orbitals on flourine to form 6  bonds. d 2 sp 3 - hybrid orbitals x y z 90 0

EXAMPLES 36 electrons … 8 bonding d 2 sp 3 hybrids Describe the molecular structure and bonding in XeF 2 and XeF 4 Xe F F F F Square planar 4 x 6 on the F atoms … 32 used so 4 more on Xe 6 electron pairs about Xe … octahedral

EXAMPLES XeFF 5 electron pairs …. Trigonal bipyrimid dsp 3 hybrids Describe the molecular structure and bonding in XeF 2 and XeF 4 Molecule is linear