1 chapter 9 orbitals and covalent bond. 2 atomic orbitals dont work n to explain molecular geometry....

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Chapter 9Chapter 9

Orbitals and Covalent BondOrbitals and Covalent Bond

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Atomic Orbitals Don’t Atomic Orbitals Don’t WorkWork to explain molecular geometry.to explain molecular geometry.

In methane, CHIn methane, CH44, the shape is , the shape is tetrahedral.tetrahedral.

The valence electrons of carbon The valence electrons of carbon should be two in s, and two in p.should be two in s, and two in p.

The p orbitals would have to be at The p orbitals would have to be at right angles.right angles.

The atomic orbitals change when The atomic orbitals change when making a molecule. making a molecule.

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9.1 Hybridization9.1 Hybridization We blend the s and p orbitals of We blend the s and p orbitals of

the valence electrons and end up the valence electrons and end up with the tetrahedral geometry.with the tetrahedral geometry.

We combine one s orbital and 3 p We combine one s orbital and 3 p orbitals.orbitals.

The atoms are responding as The atoms are responding as needed to give the needed to give the minimum minimum energyenergy for the molecule.for the molecule.

spsp33 hybridization has tetrahedral hybridization has tetrahedral geometry.geometry.

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In terms of energyIn terms of energyIn terms of energyIn terms of energyE

nerg

y

2p

2s

Hybridization sp3

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How we get to hybridization - How we get to hybridization - CHCH44

We know the geometry from We know the geometry from experiment. Four bonds of equal length experiment. Four bonds of equal length and strength.and strength.

We know the orbitals of the central We know the orbitals of the central atom. Hybridizing atomic orbitals can atom. Hybridizing atomic orbitals can explain the geometry.explain the geometry.

So if the geometry requires a So if the geometry requires a tetrahedral shape, it is sptetrahedral shape, it is sp33 hybridized. hybridized.

This includes bent and trigonal This includes bent and trigonal pyramidal molecules because one of the pyramidal molecules because one of the spsp33 lobes holds the lone pair. lobes holds the lone pair.

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(YDVD)(YDVD)

QuickTime™ and aCinepak Codec by Radius decompressor

are needed to see this picture.

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spsp22 hybridization hybridization CC22HH44 Trigonal planar. 120° Trigonal planar. 120°

Double bond acts as one pair. This Double bond acts as one pair. This results in 3 effective pairs surrounding results in 3 effective pairs surrounding the carbon atoms.the carbon atoms.

One s and two p orbitals hybridize into One s and two p orbitals hybridize into 3 identical orbitals of equal length and 3 identical orbitals of equal length and energy to make spenergy to make sp22 orbitals. orbitals.

This leaves one p orbital unhybridized.This leaves one p orbital unhybridized.

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nerg

y

2p

2s

sp2Hybridization

2p

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Two types of BondsTwo types of Bonds Sigma bonds (Sigma bonds () form from the overlap of ) form from the overlap of

orbitals along the internclear axis.orbitals along the internclear axis. Pi bond (Pi bond () occupies the space above and ) occupies the space above and

below internclear axis.below internclear axis. Between adjacent unhybridized p orbitals.Between adjacent unhybridized p orbitals. The double bond always consists of one The double bond always consists of one

bond and one bond and one bond. bond. C-C double bond C-C double bond (BDVD)(BDVD)

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and and bonds bonds(YDVD)(YDVD)

CCH H

HH



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sp hybridizationsp hybridization COCO22

Each carbon has two hybridized Each carbon has two hybridized orbitals 180º apart. Also 2 orbitals 180º apart. Also 2 unhybridized p orbitals.unhybridized p orbitals.

p orbitals are at right angles (Fig. p orbitals are at right angles (Fig. 9.17)9.17)

Makes room for two p bonds and Makes room for two p bonds and two sigma bonds.two sigma bonds.

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nerg

y

2p

2s

Hybridizationsp

2p

13



(YDVD)

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COCO22 C can make two s and two pC can make two s and two p O can make one s and one pO can make one s and one p (Fig. 9.19) (Fig. 9.19)

CCOO OO

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dspdsp33

PClPCl55 Five pairs of electrons around the Five pairs of electrons around the

central atom. Trigonal bypyramidal. central atom. Trigonal bypyramidal. Only Only bonds no bonds no bonds. bonds.

The model predicts that we must use The model predicts that we must use the d orbitals.the d orbitals.

Five electron pairs require dspFive electron pairs require dsp33 hybridization. (Fig. 9.21)hybridization. (Fig. 9.21)

There is some controversy about how There is some controversy about how involved the d orbitals are.involved the d orbitals are.

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dd22spsp33

SFSF66

Six pairs of electrons around the Six pairs of electrons around the central atom.central atom.

Octahedral shape. (Fig. 9.23)Octahedral shape. (Fig. 9.23)

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How do we figure this out?How do we figure this out? UseUse the Localized Electron Model.the Localized Electron Model. Draw the Lewis structure(s).Draw the Lewis structure(s). Determine the arrangement of Determine the arrangement of

electron pairs (VSEPR model).electron pairs (VSEPR model). Specify the necessary hybrid Specify the necessary hybrid

orbitals based upon the pairs of orbitals based upon the pairs of electrons around the central atom.electrons around the central atom.

1 chapter 9 orbitals and covalent bond. 2 atomic orbitals dont work n to explain molecular geometry....

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