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