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Van der Waals Forces. Johannes Diderik van der Waals . Polarity. Separation of charge An asymmetrical difference in electronegativity along a bond or in a molecule. Cl. Al. O. N. Cl. H. H. H. Cl. H. H. Cl. S. O. C. O. Cl. C. Cl. H. H. Cl.

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Van der waals forces l.jpg

Van der Waals Forces

Johannes Diderik van der Waals


Polarity l.jpg
Polarity

Separation of charge

An asymmetrical difference in electronegativity along a bond or in a molecule


Circle the polar molecules label d and d l.jpg

Cl

Al

O

N

Cl

H

H

H

Cl

H

H

Cl

S

O

C

O

Cl

C

Cl

H

H

Cl

Circle the polar molecules. Label d+ and d-

d-

d-

d+

d-

d+

d+


Slide4 l.jpg

Non-Polar

104.5o

C. __________ molecules are symmetrical

 D. What is the bond angle in H2O? _______

 E. The motion of particles in these phases: Solid Liquid Gas

http://itl.chem.ufl.edu/2045_s00/lectures/FG11_001.GIF


Van der waals forces5 l.jpg
Van der Waals Forces

Small, weak interactions between molecules


Van der waals forces6 l.jpg
Van der Waals Forces

Intermolecular: between molecules (not a bond)

Intramolecular: bonds within molecules (stronger)


What is being attracted l.jpg
What is being attracted?

d+ attracted to d-

 electrostatic attraction

e- s of one atom to another atom’s nucleus

e-

+

+

e-


Evidence of vdw forces l.jpg

O

O

O

O

O

O

O

O

O

O

O

O

C

C

C

C

C

C

C

C

C

C

C

C

O

O

O

O

O

O

O

O

O

O

O

O

Evidence of VDW Forces?

Non-polar molecules can form gases, liquids and solids.

Ex: CO2


3 types of van der waals forces l.jpg
3 Types of Van der Waals Forces

1)dipole-dipole

2)dipole-induced dipole

3) dispersion


Dipole dipole l.jpg
Dipole-Dipole

Two polar molecules align so that d+ and d- are matched (electrostatic attraction)

Ex: ethane (C2H6) vs. fluromethane (CH3F)


Slide11 l.jpg

Fluoromethane (CH3F) – boiling point = 194.7 K

H H H H

H C C H H C C H

H H H H

Dipole-Dipole

NOT Dipole-Dipole

d-

d+

d+

d-

polar or non-polar?

H H

H C F H C F

H H

Ethane (C2H6) – boiling point = 184.5 K

polar or non-polar?


Try this l.jpg

Br

Br

K

K

Try This:

Draw two KBr molecules and draw their dipole-dipole interactions with a dashed line.


What does to induce mean l.jpg
What does to “induce” mean?

  • To cause or bring about

    Ex:

    Induced vomiting

    Induced labor

    Induced coma


Dipole induced dipole l.jpg
Dipole-Induced Dipole

A dipole can induce (cause)

a temporary dipole to form in a

non-polar molecule

The molecules then line up

to match d+ and d- charges


Example l.jpg

Cl

d+

d-

H

Example

e-

e-

e-

e-

Ar

e-

e-

d-

d+

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

INDUCED

DIPOLE

non-polar

A DIPOLE

(it’s polar)

Dipole – Induced Dipole

(weak and short-lived)


Draw co 2 aq l.jpg

O

H

H

O

O

C

C

O

O

Draw CO2 (aq)

What does (aq) mean?

dissolved in WATER

So…draw CO2 (g) in H2O (l)

d+

d-

d+

d-

d+

d-


Where is co 2 aq seen l.jpg
Where is CO2 (aq) seen?

Carbonated water

CO2 is not very soluble…

1 CO2 in 1000 H2O molecules

http://www.packaging-technology.com/contractor_images/venus/4_rinser.jpg


Dispersion forces l.jpg
Dispersion Forces

A temporary dipole forms in a

non-polarmolecule…

which leads to…

a temporary dipole to form in ANOTHERnon-polar molecule

Dispersion is the ONLY intermolecular attraction that occurs between non-polar molecules


Dispersion forces19 l.jpg

d-

d+

d+

d-

Dispersion Forces

e-

e-

e-

e-

e-

e-

Cl-Cl

e-

e-

Cl-Cl

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

INDUCED

DIPOLE

TEMPORARY

DIPOLE

non-polar

non-polar

Dispersion

(weakest and very short-lived)


Tokay gecko dispersion forces l.jpg
Tokay Gecko:Dispersion Forces!


Review l.jpg
Review

Dipole – Dipole

between two polar molecules

Dipole – Induced Dipole

b/w a polar & a non-polar molecule

Dispersion

between two non-polar molecules


Hydrogen bonding l.jpg
Hydrogen Bonding

STRONGEST Intermolecular Force!!

A special type of dipole-dipole attraction

Bonds form due to the polarity of water

Draw 3 H2O molecules in your notes

Ice

Liquid


Hydrogen bonding con t l.jpg
Hydrogen Bonding con’t

Hydrogen bonds keep water in the liquid phase over a wider range of temperatures than is found for any other molecule of its size



Expansion of ice l.jpg
Expansion of Ice

Ice expands when water freezes compared to most substances that contract when freezing

Ice bomb video


Denisty vs temperature of h 2 o l.jpg
Denisty vs Temperature of H2O

4 oC—max density of water – liquid!

Solid

Ice

Liquid

water


Hexagonal ice l.jpg
Hexagonal Ice

http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/imgche/waterhex.gif

http://www.gala-instrumente.de/images/44%20hexagonal%20ice.jpg


Slide28 l.jpg

http://www.lummox.net/celestial/pics/ak1999-sundog.jpg

Halos, Sundogs, & Pillars are caused by hexagonal ice crystals

http://images.usatoday.com/tech/_photos/2006/09/12/cloud.jpg


Ponds freezing l.jpg
Ponds Freezing

Solid water (ice) has a lower density than liquid water


Why is this good l.jpg
Why is this good?

Ponds freeze from the top down, insulating the water below and keeping it from freezing solid

Without this, ponds would freeze solid and thaw more slowly


Surface tension l.jpg
Surface Tension

Enhancement of the intermolecular attractive forces at the surface


Evidence l.jpg
Evidence

Lab:

Dixie cup

Penny

Capillary tube

needle


What causes surface tension l.jpg
What causes surface tension?

The cohesive forces between molecules are shared with all neighboring atoms.

Since the surface has no neighboring atoms above, they exhibit stronger attractive forces for their neighbors next to and below them



How many drops can you get on a penny l.jpg
How many drops can you get on a penny? forces

Water?

TTE?

Why is there a difference???

Water has strong Hydrogen Bonds and TTE has weaker intermolecular forces

http://www.msnucleus.org/membership/html/k-6/wc/water/1/images/penny.jpg


How is surface tension affected by soap l.jpg
How is surface tension affected by soap? forces

Breaks the surface tension!

http://www.chemistryland.com/CHM107/Water/SoapDisruptsWater.jpg

http://www.chemistry.nus.edu.sg/2500/micelle.jpg


Capillary rise l.jpg
Capillary Rise forces

glass

Water rises up the capillary tube because there are unbalanced forces between the water and glass and the water and gravity

gravity

H2O Hg


Which is larger adhesion or cohesion l.jpg
Which is larger? forcesAdhesion or Cohesion?

Adhesion: attraction between H2O (Hg) & glass

Cohesion: attraction of H2O (Hg) molec. to each other

Adhesion > Cohesion

Cohesion > Adhesion


Do other liquids exhibit capillary rise l.jpg
Do other liquids exhibit capillary rise? forces

As long as they are attracted to glass and have enough cohesion


Im forces and interactions between liquids and surfaces l.jpg
IM forces and interactions between liquids and surfaces forces

Cohesion > Adhesion

Liquid “Beads”

on Surface

Cohesion < Adhesion

Liquid “Wets”

the Surface


Evaporation l.jpg
Evaporation forces

Diagram the distribution of kinetic energy at a temperature

5oC

25oC

75oC

# particles

low KE

ave KE

high KE


Which molecules will evaporate l.jpg
Which molecules will evaporate? forces

This lowers the total kinetic energy (temperature) of the entire system

Only high energy molecules can vaporize

# particles

low KE

ave KE

high KE


Boiling l.jpg

P forcesvap

Pvap

P atm

P atm

P atm

Pvap

t = 0 min

t = 5 min

BOILING!

t = 1 min

Boiling

Pvap= Patm


Boiling45 l.jpg
Boiling forces

Boiling occurs when

Vapor Pressure = Barometric Pressure

When Vapor Pressure = 760 mmHg, Boiling Point = 100oC


Evaporation questions l.jpg
Evaporation Questions forces

  • Why do we sweat?

    breaking water’s bonds has a cooling effect

    high energy molecules are lost


2 why does water stay cool in clay containers l.jpg
2 forces. Why does water stay cool in clay containers?

Since clay is porous, high energy molecules escape leaving lower temperature water

When the water added to the sand evaporates in the Pot-in-Pot Cooler, it pulls heat from the smaller pot, keeping vegetables cool.

Refrigeration for the other 90%

http://www.juneauempire.com/images/050406/13484_500.jpg

http://www.npr.org/templates/story/story.php?storyId=11032381&sc=emaf


3 why can liquid water change to vapor at room temperature l.jpg
3. Why can liquid water change to vapor at room temperature? forces

High energy molecules escape

Evaporation occurs at all temperatures

# particles

low KE

ave KE

high KE


Slide49 l.jpg

4. Define vapor pressure forces

Force of particles leaving a liquid

Pressure of molecules in their bubbles

Can solids have a vapor pressure?

Yes! Solid Gas

Ex: ice, dry ice, plastics


Slide50 l.jpg

5. What is the difference between evaporation and boiling? forces

Evaporation: occurs at any temperature; high energy molecules escape

Boiling: occurs when atmospheric pressure = vapor pressure


Volatile substances l.jpg
Volatile Substances forces

Easily evaporate

Weak attractive forces

Low boiling point

High vapor pressure


Non volatile substances l.jpg
Non-volatile substances forces

Do not easily evaporate

Strong attractive forces

High boiling point

Low vapor pressure


Equilibrium l.jpg
Equilibrium forces

A + B C + D

Forward Reaction

Reverse Reaction

Rate of forward reaction =

Rate of reverse reaction


Dynamic equilibrium l.jpg
Dynamic Equilibrium forces

Acetone (l) Acetone (g)

Reaction looks like it has stopped,

but is dynamic at the molecular level


What conditions are necessary for equilibrium l.jpg
What conditions are necessary for equilibrium? forces

  • Closed System

  • Rate of fwd rxn = rate of rev rxn

  • Constant temp, pressure, color

  • Both reactants and products are present (but not necessarily equal)


Henri louis le chatlier 1850 1936 l.jpg
Henri Louis Le Chatlier forces(1850-1936)

Inventor of acetylene torch

Professor of Industrial Chemistry and Metallurgy

Instrumental in the development of cement and Plaster of Paris


Lechatlier s principle l.jpg
LeChatlier’s Principle forces

When a stress is applied

to a system at equilibrium,

the system will respond

to partially undo the stress

Add Reactant, Add Product, Remove Reactant, Remove Product, Add Heat, Increase Pressure,…


Predicting adjustments l.jpg
Predicting adjustments forces

produced

Haber process

N2 + 3 H2 2 NH3 + energy

used

produced

used

Use energy

Produce NH3


Slide59 l.jpg

produced forces

used

produced

used

2 H+ + 2 CrO42-Cr2O72- + H2O

ORANGE

(Add H+)

Use H+

(Use H+)

Produce H+

YELLOW

H+

H+

H+

Na+


2 h 2 cro 4 2 cr 2 o 7 2 h 2 o l.jpg
2 H forces+ + 2 CrO42-Cr2O72- + H2O

Add H+

X= CrO4-2

O= Cr2O7-2

x x xx x x

x x xox xx

x x x xx xxxx

o x x x x

x x x x

ox o oo o

o o ooo o

o o x o oo oo

oo o ooo

oo

Add OH-


Slide61 l.jpg

produced forces

used

produced

used

2 NO2 N2O4 + energy

DARKER

Use Heat

LIGHTER

Produce Heat

LIGHTER

Decrease Pr.


Slide62 l.jpg

produced forces

used

produced

used

H2O (l) + energy H2O (g)

Use Heat

Evaporation

Produce Heat

Condensation

Evaporation

Increase Pr.

Decrease Pr.

Condensation


How do pressure cookers work l.jpg
How Do Pressure Cookers Work? forces

Pressure cookers increase the pressure above the water so that water boils at a ________ temperature and cooks food ________

HIGHER

http://www.goalfinder.com/images/SPGPRO2/pressur-design-of-pressure-cooker.jpg

QUICKER


Lab practice problem l.jpg
Lab Practice Problem forces

NaCl Na+ + Cl-

a) Which direction would the reaction shift if MgCl2 (Mg2+ and Cl-) were added to the system above? Explain.

b) What would happen to the amount of NaCl if Cl- were removed from the system? Explain.

Cl-

Cl-

Na+

Cl-

Cl-

Cl-

Cl-

Na+

Cl-

Na+

Na+

Cl-

Na+

NaCl

NaCl

NaCl

NaCl

NaCl

NaCl


Phase changes l.jpg
Phase Changes forces

105

DKE

DPE

100

DKE

Temperature (oC)

DPE

0

DKE

Where is there a DKE?

Where is there a DPE?

- 5

Time


Terms l.jpg
Terms forces

Melting Point

Temp when substances changes from l  s

Boiling point

Temp when substance changes from l  g

DKE—

where there is a change in temperature

DPE—

where there’s a phase change

(constant temp)


Calculations l.jpg
Calculations forces

  • Calculate the amount of heat needed to raise the temperature of 100 ml of water from 15oC to 65oC.

DQ = mcDT

DQ = (100g)(1 cal/goC)(50oC)

DQ = 5000 cal


Slide68 l.jpg

3. Calculate the amount of heat needed to melt 100 g of ice. forces

REMEMBER: Heat of Fusion = 80 cal/g

80 cal

x cal

x = 8000 cal

=

1 g

100 g


Slide69 l.jpg

2. Calculate the amount of heat needed to boil 100 ml of water.

HEAT OF VAPORIZATION = 540 cal/g

540 cal

x cal

x = 54,000 cal

=

1 g

100 g


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