Lewis structures/VSEPR/FC

• Count electrons in

• Basic attachments

• Subtract electrons used in attachments

• Put electrons on outer atoms

– Extra electrons go on inner atom– Extra electrons go on inner atom

– Deficient in electrons – use multiple bonds

• May have resonance structures

• FC may help determine which is more reasonable (e- in bonds go to higher e- neg atom)

• e- positions determine e- shape around central atom

• Atom positions determine shape of molecule

Names of shapes:

Electron positions – “lone” (unshared pairs) prefer “more room”

Especially important in trig bipyramidal and octahedral

Bond angles – determine after placing ALL electronsBond angles – determine after placing ALL electrons

C – 4 bonds, N and O total of 4 pr electrons

Bond angle

Shape of electronsShape of electrons

Shape of atoms connections

d- orbitals will be used in expanded octets

hybridization

• VSEPR predicts bond angles but in 1930’s

Linus Pauling used atomic orbitals to to

predict these same bond angles

– Valence bond theory� hybridized orbitals– Valence bond theory� hybridized orbitals

– Atomic orbitals do not have these shapes

• Hybridized orbitals – belong to molecules

When atoms form molecules

• Electrons are more “directional”

C 1s 2s 2p � 1s 2s 2p

_ _ _ _ _ _ _ _ _ _

Explanation for bond angles seen in molecules

Hybridization

• s, p, d shapes fit the same shapes and bond

angles as VSEPR

Add to your chartFig 7.4 Pg 177 fig 7.5Fig 7.4

CN Shape (VSEPR) hybridization

2 Linear sp

3 Trigonal planar sp2

4 Tetrahedral sp34 Tetrahedral sp3

5 Trigonal bipyramid sp3d

6 octahedral sp3d2

Bond angle

Shape of electrons

Add hybridization

Shape of electrons

Shape of atoms connections

Are all electrons added?Note: electrons not added

σ and π bonding

• Single bonds – sigma – end to end overlap of

orbitals – electron density between nuclei

• Multiple bonds – 1 sigma and 1or 2 pi bonds

• Pi bonds – side to side overlap – electron • Pi bonds – side to side overlap – electron

density above and below nuclei

• Pi bonds weaker than sigmas

– Therefore double bond less than twice as strong

as single bond

C2 H4

FIX FOR SP2

Acetylene – 1 sigma, 2 pi’s

C2 H2

Pi bonds

• Overlap of unhybridized p orbitals

• C2H6 C2H4 C2H2

Delocalized electrons

• Pi orbitals can be delocalized over several

atoms

• Alternating =‘s

NH

O

CH3

Place H’s and e-’s

Box sp3

Triangle sp2

Circle atoms with delocalized pi electrons

NH O

OH

CH3

CH3CH3CH3 CH3

OH

OH

H

11

16

12

15

13

14

10

5

3

4

9

8

NH6

7

NH1

2

H

H

NN

NH2

N N

NNH

O

O

OH

OH

OH

CH3

CH3

H

H

H

HH

N

N

NH