1 polarity polar bonds bonds between atoms polar molecules polarity between molecules occurs...
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POLARITY
POLAR BONDS Bonds between atoms
POLAR MOLECULES Polarity between molecules Occurs when polar bonds create a dipole moment
Bond PolarityBond Polarity
HCl is POLAR because it has a positive end and a negative end.
Cl has a greater share in bonding electrons than does H.
Cl has a greater share in bonding electrons than does H.
Cl has slight negative charge (-d) and H has slight positive charge (+ d)
H Cl••
••
+ -••H Cl
••
••
+ -••
Bond PolarityBond PolarityWhich bond is more polar (or DIPOLAR)?
O—H O—F
3.5 - 2.1 3.5 - 4.0
1.4 0.5
OH is more polar than OF
and polarity is “reversed.”and polarity is “reversed.”
O H+-
O F+ -
O H+-
O F+ -
Molecular Polarity
Molecules—such as HCl and H2O— can be POLAR
(or dipolar).
They have a DIPOLE MOMENT. The polar HCl molecule will turn to align with an electric field.
Figure 9.15
Molecular PolarityMolecular PolarityMolecules will be polar if
a)bonds are polar
AND
b)the molecule is NOT “symmetric”
All above are NOT polar
Polar or Nonpolar?
Compare CO2 and H2O. Which one is polar?
Polar or Nonpolar?
• Consider AB3 molecules: BF3, Cl2CO, and NH3.
Molecular Polarity, BF3 Molecular Polarity, BF3 F
F FB
F
F FB
B atom is positive and F atoms are negative.
B—F bonds in BF3 are polar. B—F bonds in BF3 are polar.
But molecule is symmetrical and NOT polarBut molecule is symmetrical and NOT polar
Molecular Polarity, HBF2Molecular Polarity, HBF2
B atom is positive but H & F atoms are negative.
H
F FB
H
F FB
B—F and B—H bonds in HBF2 are polar. But molecule is NOT symmetrical and is polar.B—F and B—H bonds in HBF2 are polar. But molecule is NOT symmetrical and is polar.
Is Methane, CH4, Polar?Is Methane, CH4, Polar?
Is CH3F Polar?Is CH3F Polar?
BONDING/FORCES• INTRAMOLECULAR FORCES
– Ionic– Covalent– Metallic
• INTERMOLECULAR FORCES– Van der Waal’s Forces
• London dispersion• Dipole-Dipole• Hydrogen Bonding
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Bonding, Intermolecular Forces (IMF)
IMF < intramolecular forces (covalent, metallic, ionic bonds)
IMF strength: solids > liquids > gases Boiling points and melting points are good
indicators of relative IMF strength.
Summary of IMF
Van der Waals forces
Types of Crystalline Solids
Type Particles ForcesNotable
propertiesExample
s
Atomic AtomsLondon
dispersion
Poor conductors
Very low MP
Ar (s),Kr (s)
TypeParticle
sForces
Notable properties
Examples
Molecular
Molecules
(polar or non-
polar)
London dispersion, dipole-
dipole, H-bonds
Poor conductors
Low to moderate MP
CO2 (s),
C12H22O11,
H2O (s)
SucroseCarbon dioxide (dry ice)Ice
TypeParticl
esForces
Notable properties
Examples
Ionic
Anions and
Cations
Electrostatic attractions
Hard & brittle
High MPPoor conductors
Some solubility in H2O
NaCl,Ca(NO3)2
TypeParticle
sForces
Notable properties
Examples
Covalent (a.k.a.
covalent network)
Atoms bonded
in a covalent network
Covalent bonds
Very hardVery high MP
Generally insoluble
Variable conductivity
C (diamond
& graphite)
SiO2
(quartz)
Ge, Si, SiC, BN
DiamondGraphite
SiO2
Type Particles ForcesNotable
propertiesExample
s
Metallic
Metal cations in a diffuse, delocalized e- cloud /
sea of e-
Metallic bonds
Excellent conductors
MalleableDuctileHigh but wide range of MP
Cu, Al, Fe
