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Why is this needle floating?. Intermolecular Forces:. (inter = between) between molecules. and the temperature (kinetic energy) of the molecules. What determines if a substance is a solid, liquid, or gas?.

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Intermolecular Forces:

(inter = between) between molecules

and the temperature (kinetic energy) of the molecules.

What determines if a

substance is a solid,

liquid, or gas?


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Gases: The average kinetic energy of the gas molecules is much larger than the average energy of the attractions between them.

Liquids: the intermolecular attractive forces are strong enough to hold the molecules close together, but without much order.

Solids: theintermolecular attractive forces are strong enough to lock molecules in place (high order).

Are they temperature

dependent?


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The strengths of intermolecular forces are generally weaker than either ionic or covalent bonds.

16 kJ/mol (to separate molecules)

+

-

+

-

431 kJ/mol (to break bond)


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Types of intermolecular forces ( than either ionic or covalent bonds.between neutral molecules):

Dipole-dipole forces: (polar molecules)

..

+

S

..

:

dipole-dipole attraction

:

O

O

:

..

-

-

..

+

S

..

:

:

O

O

:

..

-

-

What effect does this attraction have on the boiling point?


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Polar molecules have than either ionic or covalent bonds.

dipole-dipole attractions for

one another.

+HCl----- +HCl-

dipole-dipole attraction


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Types of intermolecular forces ( than either ionic or covalent bonds.between neutral molecules):

Hydrogen bonding: cases of very strong dipole-dipole interaction (bonds involving H-F, H-O, and H-N are most important cases).

+H-F- --- +H-F-

Hydrogen bonding


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Hydrogen bonding is a weak to moderate attractive force that exists between a hydrogen atom covalently bonded to a very small and highly electronegative atom and a lone pair of electrons on another small, electronegative atom (F, O, or N).


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Boiling points versus molecular mass exists between a hydrogen atom covalently bonded to a

100

0

-100

Predict a trend for: NH3, PH3, AsH3, and SbH3


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Predict a trend for: exists between a hydrogen atom covalently bonded to a NH3, PH3, AsH3, and SbH3

SbH3

NH3

AsH3

PH3


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Now let’s look at HF, HCl, HBr, and HI exists between a hydrogen atom covalently bonded to a

HF

SbH3

NH3

HI

AsH3

HBr

HCl

PH3


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Types of intermolecular forces ( exists between a hydrogen atom covalently bonded to a between neutral molecules):

London dispersion forces: (instantaneous dipole moment)

( also referred to as van der Waal’s forces)

attraction

-

+

-

+

“electrons are shifted to overload one side of an atom or molecule”.


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polarizability: the ease with which an atom or molecule can be distorted to have an instantaneous dipole. “squashiness”

In general big molecules

are more easily polarized

than little ones.

Big and

“squashy”

little


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Which one(s) of the above are most polarizable? be distorted to have an instantaneous dipole. “

Hint: look at the relative sizes.


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Other types of forces holding solids together: be distorted to have an instantaneous dipole. “

ionic: “charged ions stuck together by their charges”

There are no individual molecules here.


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Metallic bonding: be distorted to have an instantaneous dipole. ““sea of electrons”

Copper wire: What keeps the atoms together?

Cu atoms

an outer shell electron

To which nucleus does the electron belong?


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Metallic Bonding: “sea of e be distorted to have an instantaneous dipole. “-’s”


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Covalent Network: (diamonds, quartz) be distorted to have an instantaneous dipole. “very strong.

1.42 Å

1.54 Å

3.35 Å

What type of hybridization is present in each?


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Pentane isomers: C be distorted to have an instantaneous dipole. “5H12

neo-pentane

n-pentane

iso-pentane

Hvap=22.8 kJ/mol

Hvap=24.7 kJ/mol

Hvap=25.8 kJ/mol

All three have the same formula C5H12

Why do they have different enthalpies of vaporization?

London and “Tangling”


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C-C-C-C be distorted to have an instantaneous dipole. “

C

iso-pentane

C

C-C-C

C

neo-pentane

Hvap=24.7 kJ/mol

Hvap=22.8 kJ/mol

n-pentane

Hvap=25.8 kJ/mol

London and “Tangling”


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Structure effects on boiling points be distorted to have an instantaneous dipole. “


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Ion-dipole interactions: such as a salt dissolved in water be distorted to have an instantaneous dipole. “

cation

polar molecule

anion


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Phase changes: be distorted to have an instantaneous dipole. “

solid  liquid (melting  freezing)

liquid  gas (vaporizing  condensing)

solid  gas (sublimation  deposition)


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Energy changes accompanying phase changes be distorted to have an instantaneous dipole. “


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Heating curve for be distorted to have an instantaneous dipole. “1 gram of water


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Heating curve for be distorted to have an instantaneous dipole. “1 gram of water

Specific Ht. Steam = 1.84 J/g•K

Hvap=2260 J/g

Specific Heat of water = 4.184 J/g•K

Hfus=334 J/g

Specific Heat of ice = 2.09 J/g•K


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Calculate the enthalpy change upon converting 1 mole of water from ice at -12oC to steam at 115oC.

gas

115oC

liquid

100oC

gas

100oC

liquid

0oC

solid

-12oC

solid

0oC

H1 + H2 + H3 + H4 + H5 = Htotal

Sp. Ht. + Hfusion + Sp. Ht. + HVaporization + Sp. Ht. = Htotal

Specific Heat of ice = 2.09 J/g•K

Hfus=334 J/g

Hvap=2260 J/g

Specific Heat of water = 4.184 J/g•K

Specific Ht. Steam = 1.84 J/g•K


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Calculate the enthalpy change upon converting 1 mole of water from ice at -12oC to steam at 115oC.

gas

115oc

liquid

100oC

gas

100oc

liquid

0oC

solid

-12oC

solid

0oC

H1 + H2 + H3 + H4 + H5 = Htotal

Sp. Ht. + Hfusion + Sp. Ht. + HVaporization + Sp. Ht. = Htotal

Specific Heat of ice = 2.09 J/g•K

Hfus=334 J/g

Specific Heat of water = 4.184 J/g•K

Specific Ht. Steam = 1.84 J/g•K


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Vapor pressure water from ice at -12


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VAPOR PRESSURE CURVES water from ice at -12

A liquid boils when its vapor pressure =‘s the external pressure.


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normal boiling point is the temperature at which a water from ice at -12

liquid boils under one atm of pressure.

pressure = 1 atm

vapor pressure = 1 atm

liquid

BOILING


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PHASE DIAGRAMS: (Temperature vs. Pressure) water from ice at -12

gas and liquid are

indistinguishable.

critical temperature

and critical pressure

(all 3 phases exists here)


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H water from ice at -122O

CO2

note slope with pressure

note slope with pressure


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Crystal Structures: water from ice at -12


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unit cells: water from ice at -12

contains 2 atoms

contains 1 atom