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