Lewis Structures• H is always a terminal atom• The atom with the lowed EN is the central atom• Find the total # of valence (ions add and lose
electrons)• Bond each atom to the central atom with a single
bond• Place lone pairs around terminal atoms to complete
their octet• Add remaining electrons to central atom• Use multiple bonds to complete the octet of the
central atom
Exceptions to the Octet Rule
• Hydrogen only gets 2• Boron is a moron, he likes 6 electrons• Expanded Valence – 3rd energy level or higher
HYBRID ORBITALS
covalent bonds are formed by overlap of atomic orbitalsatomic orbitals on the central atom can mix and exchange their character – hybridization
ONLY BONDS ARE FORMED FROM
OVERLAP OF HYBRIDS ORBITALS ARE NOT FORMED FROM HYBRID ORBITALS
Number of Number of electron electron
structural structural pairspairs
Atomic Atomic orbitalsorbitals
Hybrid Hybrid orbitals orbitals formedformed
GeometryGeometry
22 one s + one pone s + one p two sp two sp AX2: linear
33 one s + two pone s + two p three spthree sp22 AX3: trigonal planar
44one s + three one s + three
ppfour spfour sp33 AX4: tetrahedral
55s + three p + s + three p +
one done d five spfive sp33d d AX5
: trigonal bipyramidal
66one s + three one s + three
p + two dp + two d six spsix sp33dd22 AX6: octahedral
practice
2 sp Hybrids Formed From an s and p
3 sp2 Hybrids Formed From an s and 2 p’s
Forming sigma bonds• Three ways atoms can form a sigma bond:– 2 hydrogen atoms’ 1s orbitals overlap
– a hybrid orbital overlaps a hydrogen’s 1s orbital
– 2 hybrid orbitals overlap end-to-end
Forming pi bonds• Pi bonds form when– atoms are already bonded with a sigma bond– both atoms have a leftover p orbital
• Pi bonds form when two atoms’ p orbitals overlap side-by-side
NO21- Resonance Structures
next formal charge
Delocalized pi bonding in CO3–2
• In the CO3–2 ion, one pi bond is delocalized
over three C-O connections• The C atom and all three O atoms are sp2
hybridized and have a leftover p orbital• The four p orbitals overlap side-to-side to
create the pi bonding
O
O
C OO
O
C O O
O
C O
C6H6, Benzene an Important Molecule With Resonance
Delocalized e- due to resonance explains why the bonds in benzene
are identical.
LINEAR
AX2 EXAMPLE BH2
AX2 WITH DOUBLE BOND CO2
AX3 EXAMPLE BH3
TRIGONAL PLANAR
O
O
C O
structural pairs on central atom 3
structural pair geometry trigonal planar
molecular geometry trigonal planar
bond angle(s) 120
AX4EXAMPLE CH4
AX3E EXAMPLE NH3
PYRAMIDAL
AX2E2 EXAMPLE H2S
BENT
AX5 EXAMPLE PCl5
TRIGONAL BIPYRAMIDAL
AX4E EXAMPLE SF4
SEE SAW
AX3E2 EXAMPLE BF3
T SHAPE
EXAMPLE XeF2
LINEAR
structural pairs on central atom 5
structural pair geometry trigonal bipyrimid
molecular geometry T-shaped
bond angle(s) 90 , 180
O Xe F
F
Next resonance
structural pairs on central atom 5
structural pair geometry trigonal bipyrimid
molecular geometry see-saw, flying goosedistorted tetrahedron
bond angle(s) 120 , 90 , 180
SF F
F
F
EXAMPLE SeF6
OCTAHEDRAL
EXAMPLE IF5
SQUARE PYRAMIDAL
EXAMPLE XeF4
SQUARE PLANAR
structural pairs on central atom 6
structural pair geometry octahedron
molecular geometry octahedron
bond angle(s) 90 , 180
S FF
FF
FF
Polar molecules• A compound’s polarity can be measured
experimentally as its dipole moment• Polar molecules align themselves with an
electrical field
+ –
+ –
+ –
+ –
+ –+ –
+ – + –
+ – +++
+++
–––
–––
Polar molecules• The C=O bond is polar• But the dipole
moment of CO2 is zero
• CO2 is not a polar molecule
O C O
ExamplesExamples
SO2
• S-O bonds are polar• Geometry is bent (120°)• sp• Bond dipoles don’t cancel• SO2 is polar
SO3
• S-O bonds are polar• Geometry is trigonal
planar• sp2
• Bond dipoles do cancel• SO3 is nonpolar
O S O O S O
O
Examples
HH22OO
• H-O bonds are polarH-O bonds are polar• Geometry is bent (109.5°)Geometry is bent (109.5°)• spsp• Bond dipoles don’t cancelBond dipoles don’t cancel• HH22O is polarO is polar
OClOCl22
• O-Cl bonds are nonpolarO-Cl bonds are nonpolar• spsp• OClOCl22 is nonpolar is nonpolar
H O H Cl O Cl
SF4
• S-F bonds are polar• geometry is see saw• dsp3
• axial bond dipoles cancel• equatorial bond dipoles
don’t cancel• SF4 is polar
PF5
P-F bonds are polar• geometry is trigonal
bipyramid• dsp3
• axial bond dipoles cancel• equatorial bond dipoles
cancel• PF5 is nonpolar
SF F
F
FSF F
F
FF
XeF2
• Xe-F bonds are polar• geometry is linear
– structural pair geometry is trigonal bipyrimidal
– lone pairs in equatorial– F atoms in axial– dsp3
• bond dipoles cancel• XeF2 is nonpolar
PbH2
• Pb-H bonds are nonpolar• PbH2 is nonpolar
F Xe F
H Pb H
