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Suggested HW: Ch 9: 25, 29, 39, 43, 72(For 25 and 43, you are illustrating the hybridization of the atomic orbitals into hybrid orbitals and the overlapping of these hybrid orbitals as described in the examples provided)Lecture 11Covalent Bonding Pt 3: Hybridization (Ch. 9.5-9.13)IntroductionWe now know that atoms can bond covalently through the sharing of electrons

VSEPR theory helps us predict molecular shapes. But, it does not explain what bonds are, how they form, or why they exist.

In ch 9, chemical bonding will be explained in terms of orbitalsCovalent Bonding Is Due to Orbital OverlapIn a covalent bond, electron density is concentrated between the nuclei.

Thus, we can imagine the valence orbitals of the atoms overlapping

The region of orbital overlap represents the covalent bondOverlapping Valence OrbitalsRecall s and p orbitals (ch 5)S orbitals are spherical. L = 0, mL = 0 Max of 2 electronsP orbitals consist of two lobes of electron density.L= 1, mL = -1, 0, 1 (3 suborbitals) Max of 6 electrons

pxpyS

pzForming Sigma () BondsCovalent bond 1s1 1s1H+H+H+H+Two overlapping atomic orbitals form a molecular bonding orbital. Plus sign indicates phase of electron wave, NOT CHARGE

A sigma () bonding orbital forms when s-orbitals overlap.stabilization (energy drop)EnergyIntroduction to HybridizationImagine the molecule CH4. We know that carbon has 4 valence electrons (2s22p2).

However, when we fill our orbitals in order as according to Hunds rule, we notice there are only enough unpaired electrons to make two bonds. Stay mindful of the fact that a covalent bond involves the sharing of unpaired electrons 2s2 2p2 C 1s1 1s14 HENERGY 1s1 1s1X6Four sp3 hybrid orbitalssp3 HybridizationSo how does CH4 form? How can carbon make 4 bonds?

To make four bonds, carbon hybridizes four of its atomic orbitals. This creates four equivalent sp3 hybrid orbitals, each containing one unpaired electron. 2s2 2p2The name sp3 originates from the fact that the hybrid orbitals form as a result of the mixture of 1 s-orbital and 3 p-orbitals. Thus, each sp3 orbital is 25% s character and 75% p character

ENERGYFormation of Sigma Bonding Orbitalssp3 hybrid orbitalsENERGY 1s1 1s1 1s1 1s1C4H bonding orbitalsatomic s-orbitals

The addition of an s-orbital to a pz orbital is shown above. The s orbital adds constructively to the (+) lobe of the pz orbital and adds destructively to the lobe that is in the opposite phase (-). The symbols indicate phase, not charge.

Whenever we mix a certain number of s and p atomic orbitals, we get the same number of molecular orbitals. This is called the principle of conservation of orbitals.

s

pz+=zzIllustration of Orbital Hybridization

Illustration of sp3 Hybrid Orbitals and Orbital Overlap4 -bondsThe four hybrid orbitals arrange themselves tetrahedrally. sp2 HybridizationThe BH3 molecule gives us an example of sp2 hybrid orbitals.

Once again, we have a situation where we dont have enough bonding sites to accommodate all of the hydrogens. (Remember, B is electron deficient!) 2s2 2p1B 1s1 1s1 1s13 HENERGYX11sp2 HybridizationSo, to make 3 bonding sites, 3 hybrid molecular orbitals are formed by mixing the 2s-orbital with two 2p-suborbitals.

This forms an sp2 orbital. Each of these three hybrid orbitals are one-third s-character, and two-thirds p-character. 2s2 2p1BThree sp2 hybrid orbitalsunused 2p suborbitalENERGY

This figure illustrates the 3 hybrid orbitals combined with the unused 2p orbital, which is perpendicular to the hybrid orbitals.

sp2 orbitalsThe result of adding one s and two p orbitals together is a trigonal planar arrangement of electron domains

H+empty 2p orbitalH+H+BH bondHHsp2 Geometry and Bondingsp HybridizationImagine BeH2 (the Be-H bond is covalent), with Be having the electron configuration: [He]2s2

Here, we have a situation where no bonding electrons are available. To make two Be-H bonds, Be must create two hybrid orbitals by mixing two atomic orbitals (the 2s orbital and one of the 2p orbitals). This yields sp hybrid orbitals (50% s, 50% p) 2s2ENERGY 2p0 1s1 1s1Be2 HX

2s2ENERGY 2p0Be Two sp hybrid orbitalsunused 2p suborbitalssp HybridizationHybridization of Lone Electron PairsEx. What is the hybridization of Oxygen in H2O?The valence electron configuration of O is [He]2s2 2p4

2p4 2s2As you see, there are two unpaired O electrons. Does this mean that these two p-suborbitals can overlap with the two Hydrogen 1s orbitals without hybridizing?? ENERGYO 1s1 1s12 H

No!! The reason is that we now have two sets of lone pairs of electrons that are substantially different in energy (2s and 2p). The orbitals will hybridize to form degenerate (equal energy) sets of electrons.

Lone pair must always be equal in energy with each other, and with bonding electrons. 2p4 2s2ENERGYO 1s1 1s12 HXHOH2s electrons2p electronsHybridization of Lone Electron PairsBAD!!Water has sp3 hybridization 2p4 2s2 1s1 1s1ENERGY bondsH2OHOHsp3 electronsO2 HFour sp3 hybrid orbitalsLone pairBonding electronsSo What Do We Know So Far?Total Electron Domains Around Atom (Bond + LP)Hybridization2sp3sp24sp3Double and Triple BondingHow can orbital overlap be used to explain double and triple bonds? What kind of interactions are these?

Lets look at ethene, C2H4

CCHHHHThe hybridization of each carbon is sp2 because each is surrounded by three electron domains. The geometry around each C is trigonal planar.sp2sp2 2s2 2p2sp2 hybrid orbitalsunhybridized p-electronCCHHHHForming Double BondsCWe can see that for each carbon atom, we need three sp2 orbitals and three unpaired electrons to make three sigma bonds. But how is the double bond formed?

All double bonds consist of 1 -bond and 1 -bondDouble Bonds formed by simultaneous and interactionThe remaining p-electrons form a bond. This bond forms due to attraction between the parallel p-orbitals. The like-phase regions are drawn toward one another and overlap.H+H+H+H+Triple Bonds formed by 1 -bond and 2 -bonds.Ex. HCN

HCNspspCan you draw the orbital diagram for this molecule?ExamplesHow many and bonds are in each of the following molecules? Give the hybridization of each carbon.

CH3CH2CHCHCH3CH3CCCHCH2

sp3d and sp3d2 hybridizationAtoms like S, Se, I, Xe etc. can exceed an octet because of sp3d and sp3d2 hybridization (combination of ns, np, and nd orbitals where n>3).

This results in either trigonal bipyramidal or octahedral skeletal geometry

sp3dsp3d2Exceeding an Octet. Example: SF6 3p4 3s2Energy 3d0sp3d2 hybrid orbitalssp36 FSSF6Fluorine lone pair

SExceeding an Octet. Example: SF6

F3 lone pairunpaired electronoverlapx 6

Look Familiar ???Examples:What is the hybridization of the central atom?CO2H2COCH3CCHIF5PCl5SeOF4