Intermolecular Forces:Intermolecular Forces:

What holds What holds everything togethereverything together

(Chapter 14)(Chapter 14)

IntraIntramolecular forces (bonds)molecular forces (bonds)

Hold atoms together in moleculesHold atoms together in molecules

Have high energy associated with them Have high energy associated with them – it’s difficult to break molecules into their it’s difficult to break molecules into their

individual atomsindividual atoms

Different types based upon what is going Different types based upon what is going on with the electrons (electron clouds)on with the electrons (electron clouds)

Types of bonds:Types of bonds:

IonicIonic– attraction between fully charged molecules/ atoms attraction between fully charged molecules/ atoms

NaCl, made from NaNaCl, made from Na++ and Cl and Cl--; or ; or Ca(OH)Ca(OH)22, made from Ca, made from Ca2+2+ and 2OH and 2OH--

CovalentCovalent– electrons are shared between atoms, electrons are shared between atoms,

water (Hwater (H22O) and O) and sugar (Csugar (C66HH1212OO66))

– Can be polar or nonpolarCan be polar or nonpolarBased on Based on

– electronegativity electronegativity – VSEPR geometry (shape)VSEPR geometry (shape)

InterIntermolecular forces (IMFs)molecular forces (IMFs)Hold molecules togetherHold molecules together

Much weaker than intramolecular forcesMuch weaker than intramolecular forces– Intramolecular bonds are usually 100x or even 1000x Intramolecular bonds are usually 100x or even 1000x

strongerstronger

*(kJ are units of energy like Calories; 1Cal= 4.184kJ)*(kJ are units of energy like Calories; 1Cal= 4.184kJ)– 1000cal= 1Cal1000cal= 1Cal

– 1cal =4.184J1cal =4.184J

Figure 14.2: Intermolecular forces exist Figure 14.2: Intermolecular forces exist betweenbetween molecules. Bonds exist molecules. Bonds exist withinwithin molecules. molecules.

Why do we care?Why do we care?

The strength of the IMFs determine The strength of the IMFs determine the state of matter the state of matter – Solid, liquid, or gas*Solid, liquid, or gas*

– *Not plasma- intramolecular bonds are broken to get *Not plasma- intramolecular bonds are broken to get plasmasplasmas

shape volume density energy*motion with

Energy*

level of organizatio

n*strength of

IMFs*

Gas indefinite

variable with

P and T

variable with

volume change

high

high; molecules freely moving with

great distance compared to

molecular size between them

very low low

Liquid indefiniteconstant

**constant

**moderate

high; molecules freely moving past each other but in close proximity to

each other

low moderate

Solid definiteconstant

**constant

**low

low; vibration only as molecules are basically fixed in

place

high high

*all at room temperature, ~25C

**small variations occur due to temperature changes, very little variable with pressure changes

Solids, Liquids, and Gases

Things with strong IMFs tend to be solids at Things with strong IMFs tend to be solids at room temperatureroom temperatureThings with weak IMFs tend to be gases at room Things with weak IMFs tend to be gases at room temperaturetemperatureMedium IMFs tend to be in between- Medium IMFs tend to be in between- – liquids, yes, but with varying characteristicsliquids, yes, but with varying characteristics

Amorphous solids: long transition between solid Amorphous solids: long transition between solid and liquid states- gets soft, then melts (like wax)and liquid states- gets soft, then melts (like wax)Crystalline solids: definite, clear melting point Crystalline solids: definite, clear melting point (no soft transition- ie: ice)(no soft transition- ie: ice)

Types of IMFs Types of IMFs

In order of In order of increasingincreasing strength: strength:

– London dispersion forcesLondon dispersion forces– Dipole- dipoleDipole- dipole– Hydrogen bondsHydrogen bonds

London dispersion forcesLondon dispersion forces

LDFs occur in all molecules, but are the only LDFs occur in all molecules, but are the only forces that are present in nonpolar molecules forces that are present in nonpolar molecules such as diatomic molecules and atomic such as diatomic molecules and atomic substancessubstances– COCO22, N, N22, He, He

They occur because the electron clouds around They occur because the electron clouds around molecules are not always evenly distributed. molecules are not always evenly distributed. – When the electron clouds are unevenly distributed, When the electron clouds are unevenly distributed,

temporary partial charges resulttemporary partial charges result

Figure 14.6: Atoms with Figure 14.6: Atoms with spherical electron spherical electron

probability.probability.

14.6: The atom on the 14.6: The atom on the left develops an left develops an instantaneous instantaneous

dipole.dipole.

LDFs, con’tLDFs, con’tThese temporary partial charges These temporary partial charges are called induced or temporary are called induced or temporary dipolesdipoles– This temporary dipole forming in a This temporary dipole forming in a

nonpolar substance is strong enough nonpolar substance is strong enough to cause a dipole to occur in a to cause a dipole to occur in a neighboring moleculeneighboring molecule

Figure 14.3: Figure 14.3: (a) Interaction (a) Interaction of two polar of two polar

molecules. (b) molecules. (b) Interaction of Interaction of many dipoles many dipoles

in a liquidin a liquid..

LDFs, con’tLDFs, con’t

Basically, everything lines up temporarily, but Basically, everything lines up temporarily, but long enough to keep everything togetherlong enough to keep everything together

Common in gasesCommon in gases

See LDFs at work hereSee LDFs at work herehttp://antoine.frostburg.edu/chem/senese/101/liquids/faq/h-bonding-vs-london-forces.shtml

These dipoles These dipoles fluctuate; they do not fluctuate; they do not last very long, but last very long, but they do occur they do occur frequently enough to frequently enough to have a significant have a significant effect overalleffect overall

Dipole- dipole forces:Dipole- dipole forces:

Are stronger than LDFs because they Are stronger than LDFs because they occur in polar molecules that already have occur in polar molecules that already have permanent dipole moments (in other permanent dipole moments (in other words, partial charges already exist)words, partial charges already exist)

Are AKA as Are AKA as van der Waalsvan der Waals interactions at times, but in actuality both interactions at times, but in actuality both induced dipole attractions and dipole-dipole attractions are van der Waals induced dipole attractions and dipole-dipole attractions are van der Waals forcesforces

ExamplesExamples

HCl and other acids*HCl and other acids*

HCNHCN

NHNH33

*except HF, which does something else*except HF, which does something else

What would happen between polar and What would happen between polar and nonpolar molecules? (Do forces of nonpolar molecules? (Do forces of attraction exist? Do the molecules repel?) attraction exist? Do the molecules repel?) Explain!Explain!

Hydrogen bondingHydrogen bonding

Are stronger than dipole-dipole forces or Are stronger than dipole-dipole forces or LDFsLDFs

Occurs in only the most polar bondsOccurs in only the most polar bonds– between molecules containing H-F, H-O and between molecules containing H-F, H-O and

H-N bonds H-N bonds onlyonly

Are the reason that water is so different Are the reason that water is so different from any material from similar atoms, like from any material from similar atoms, like HH22SS

•Figure 14.4: Figure 14.4: Hydrogen bonding Hydrogen bonding among water among water molecules.molecules.

Norton Interactive: : IMFs tutorialIMFs tutorialSelect Hydrogen Select Hydrogen bonding in water from bonding in water from bottom of listbottom of list

http://www.northland.cc.mn.us/biology/Biology1111/animations/hydrogenbonds.html(note: I am not responsible for the music on the above web site)(note: I am not responsible for the music on the above web site)Polarity and hydrogen bond formationIce at different temperatures

Which is ice? Which is liquid Which is ice? Which is liquid water? Explain.water? Explain.

Ice at different temperatures

Water is special because…Water is special because…

It has a high specific heat, meaning that it takes It has a high specific heat, meaning that it takes a lot of energy to raise the temperature of a a lot of energy to raise the temperature of a sample of water by even 1 degreesample of water by even 1 degree– Specific heat of water (c)= 1 cal/ gSpecific heat of water (c)= 1 cal/ g°°C or 4.184J /gC or 4.184J /g°°CC

The solid phase is LESS dense than the liquid The solid phase is LESS dense than the liquid phase, so ice floats on waterphase, so ice floats on water

It’s a good solvent for many substances due its It’s a good solvent for many substances due its polaritypolarity

HH22O is liquid at RT, where HO is liquid at RT, where H22S is a gasS is a gas

Figure 14.5: The boiling points Figure 14.5: The boiling points of covalent hydrides.of covalent hydrides.

Water is specialWater is special

And water would not be special without And water would not be special without hydrogen bondinghydrogen bonding

H bonding plays vital roles in biological H bonding plays vital roles in biological systems systems – DNA (holding together the chains of DNA)DNA (holding together the chains of DNA)– Protein shape (and therefore the protein’s Protein shape (and therefore the protein’s

function; think hair!)function; think hair!)enzymesenzymes

IMFs in proteins

For the next slide:For the next slide:

Determine polarity of groupDetermine polarity of group

Determine type of IMFs are possible in Determine type of IMFs are possible in groupgroup

Determine if the group will be highly Determine if the group will be highly soluble in watersoluble in water

Sickle Cell Sickle Cell AnemiaAnemia

Glu (glutamic acid) replaced by Val (valine)Glu (glutamic acid) replaced by Val (valine)

synthesis

What would happen if a molecule capable What would happen if a molecule capable of H-bonding comes into contact with:of H-bonding comes into contact with:– A nonpolar substanceA nonpolar substance– A polar substance that does not H-bondA polar substance that does not H-bond

Strength increases from left to right; when ions are involved, attractive forces are Strength increases from left to right; when ions are involved, attractive forces are greater than when they are not involved. greater than when they are not involved. http://cwx.prenhall.com/bookbind/pubbooks/blb/chapter11/medialib/blb1102.htmlhttp://cwx.prenhall.com/bookbind/pubbooks/blb/chapter11/medialib/blb1102.html

Dealing with this Dealing with this pic…pic…

Ion- dipole forces Ion- dipole forces

Ionic BondingIonic Bonding– Basically electrostatic attractive Basically electrostatic attractive

forces between positive and forces between positive and negative chargesnegative charges

StrongStrong

IMFs influence…IMFs influence…

Boiling point/ Melting PointBoiling point/ Melting Point

ViscosityViscosity

Surface TensionSurface Tension

Capillary ActionCapillary Action

Vapor pressure/ rate of evaporationVapor pressure/ rate of evaporation

State of Matter (at room temp)State of Matter (at room temp)– Density falls here, but can vary even within Density falls here, but can vary even within

statestate

IMFs and massIMFs and mass

The mass of a material makes a The mass of a material makes a difference, so yes, mass (size) mattersdifference, so yes, mass (size) matters

Larger molecules have stronger forces Larger molecules have stronger forces than similar molecules that are smaller (in than similar molecules that are smaller (in terms of mass)terms of mass)

Figure 14.5: The boiling points Figure 14.5: The boiling points of covalent hydrides.of covalent hydrides.

Boiling points and masses Boiling points and masses of noble gasesof noble gases

Helium: Helium: -269°C-269°C 4.00 4.00 g/molg/mol

Neon: Neon: -246°C-246°C 20.18 20.18 g/molg/mol

Argon: Argon: -186°C-186°C 39.95 39.95 g/molg/mol

Krypton: Krypton: -152°C-152°C 83.80 83.80 g/molg/mol

Xenon: Xenon: -108°C-108°C 131.3 131.3 g/molg/mol

radon radon -62°C-62°C ~222 ~222 g/molg/mol

Larger atoms have Larger atoms have larger e- clouds, which larger e- clouds, which lead to greater lead to greater polarizabilitypolarizability

Name

Molecular Melting Boiling State at

Formula Point Point 25oC

  (oC) (oC)  

methane CH4 -183 -164 gas

ethane C2H6 -183 -89 gas

propane C3H8 -190 -42 gas

butane C4H10 -138 -0.5 gas

pentane C5H12 -130 36 gas

hexane C6H14 -95 69 gas

heptane C7H16 -91 98 gas

octane C8H18 -57 125 gas

nonane C9H20 -51 151 liquid

decane C10H22 -30 174 liquid

undecane C11H24 -25 196 liquid

dodecane C12H26 -10 216 liquid

eicosane C20H42 37 343 liquid

triacontane C30H62 66 450 solid

Saturated Hydrocarbons, or Alkanes

As melting point increases, boiling point increases

(saturated hydrocarbons are hydrocarbons with as many Hs as possible)

Shape also matters

• Butane, bp -0.5 degrees C

• 2-methylpropane -11.7 degrees C

Butane has a higher boiling point because the dispersion forces are greater. The molecules are longer (and so set up bigger temporary dipoles) and can lie closer together than the shorter, fatter 2-methylpropane molecules.

Also, the molecules can stack with each other better

Butane and 2-methylpropane

                                                                                                                                                                                                  

                                                                                                          

                                                                                    Compare the properties of these two compounds:

n-butane . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . 2-methylpropane0.601 . . . . . . . . . . . . . . . . relative density (liquid) . . . . . . . . . . . . . . . . 0.5511.348 . . . . . . . . . . . . . . . . refractive index (liquid) . . . . . . . . . . . . . . . .1.351- 0.5 . . . . . . . . . . .. . . . . . . boiling point (oC) . . . . . . . . . . . . . . . . . . .. . - 11.7- 138.3 . . . . . . . . . . . . . . . . melting point (oC) . . . . . . . . . . . . . . .. . . . - 159.6

It is clear that the different carbon skeletons make a difference to the properties, especially the melting and boiling points.

Fats v Oils:Fats v Oils:Saturated v. UnsaturatedSaturated v. Unsaturated

Molecular size, bond order, and bond Molecular size, bond order, and bond orientation:orientation:– How different IMFs result in differences in How different IMFs result in differences in

food moleculesfood molecules

A carbon exists where two lines intersectA carbon exists where two lines intersect

Atoms other than C and H are written inAtoms other than C and H are written in

Hs are not usually written out- Hs are not usually written out- – They fill in to complete octets on other atomsThey fill in to complete octets on other atoms

Random cis trans Random cis trans fatsfats

(Omega 3 (Omega 3 and and Omega 6 Omega 6 fats have fats have the double the double bonds on bonds on the 3 or 6the 3 or 6thth carbon)carbon)

fatty acids and triglyceridesfatty acids and triglycerides

3 Fatty acid chains 3 Fatty acid chains (above) join with a (above) join with a glycerol molecule (top glycerol molecule (top right) to form a right) to form a triglyceride (right, triglyceride (right, saturated)saturated)

Triglyceride formationTriglyceride formation

TriglyceridesTriglycerides

OilsOils– More More

unsaturated unsaturated FAsFAs

– Liquid at RTLiquid at RT

FatsFats– More More

saturated saturated FAsFAs

– Solid at RTSolid at RT

16C sat MP= 62.9°C 18C sat MP= 69.6°C 18C unsat MP= 13°C

Oleic v linoleic acidOleic v linoleic acid

Melting Melting Points Points °°C:C:– Oleic acid:Oleic acid: 13 13– Linoleic Acid:Linoleic Acid: -5 -5

Why?Why?

Why do the melting points differ between Why do the melting points differ between – Palmitic Acid (16 C, sat)Palmitic Acid (16 C, sat)– Stearic Acid (18 C, sat)Stearic Acid (18 C, sat)– Oleic Acid (18C, mono unsat)Oleic Acid (18C, mono unsat)– Linoleic Acid (18C, polyunsat. 2=)Linoleic Acid (18C, polyunsat. 2=)

Explain the impact of number of carbons Explain the impact of number of carbons and the number of double bonds when and the number of double bonds when answering the above questionanswering the above question

WHY DOES THIS HAPPEN?WHY DOES THIS HAPPEN?

Proximity of atoms; regular shape allows Proximity of atoms; regular shape allows the IMFs to hold everything in place (to the IMFs to hold everything in place (to “stack”) molecules rather than have the “stack”) molecules rather than have the irregular shapes slide past each otherirregular shapes slide past each other

TriglyceridesTriglycerides

In unsaturated In unsaturated triglycerides, the triglycerides, the molecules can not molecules can not stack stack

In the saturated In the saturated molecules, the fatty molecules, the fatty acids are tightly acids are tightly packed and packed and stackedstacked

More carbons, higher MPMore carbons, higher MP

The more double bonds, the lower the MPThe more double bonds, the lower the MP

Of the following, which Of the following, which would have the would have the highest MP? The highest MP? The lowest?lowest?Lauric Lauric 12C, unsat, MP +4412C, unsat, MP +44°C°C

Stearic Stearic 18C, sat, MP 7018C, sat, MP 70°C°C

Arachodonic Arachodonic 20, unsat, MP -5020, unsat, MP -50°C°C

Elmhurst

Which fats Which fats are are saturated? saturated? Unsaturated?Unsaturated?What type of What type of IMF would IMF would predominatepredominate??Rank the Rank the molecules in molecules in order from order from lowest to lowest to highest MP.highest MP.

Percent Fatty Acids in Percent Fatty Acids in

Percent Fatty acids in selected triglycerides

Cis and trans fatsCis and trans fats

CisCis- v - v TransTrans- fats- fats

Cis-Cis- fats are naturally occurring fats from animal fats are naturally occurring fats from animal productsproductsTrans-Trans- fats occur from modifying oils chemically fats occur from modifying oils chemically– Partially hydrogenating oils Partially hydrogenating oils

Adding H’s causes double bonds to convert to single bonds Adding H’s causes double bonds to convert to single bonds – Unsaturated to saturated conversionUnsaturated to saturated conversion

Due to steric hindrance, when the H is added, they convert some cis Due to steric hindrance, when the H is added, they convert some cis bonds to trans bondsbonds to trans bonds

Why do manufacturers make trans fats for use in foods?Why do manufacturers make trans fats for use in foods?– Trans fats cost less (vegetable sources v. animal sources)Trans fats cost less (vegetable sources v. animal sources)– Fats in foods are usually more desirable that oils- Fats in foods are usually more desirable that oils-

Less greasyLess greasyCan control how solid the fats are by controlling the number of Can control how solid the fats are by controlling the number of double bondsdouble bondsBetter/ easier to cook with (especially in baked goods)Better/ easier to cook with (especially in baked goods)

Saturated Fats: These are considered to be Saturated Fats: These are considered to be the “bad” fats. the “bad” fats. – called “saturated” because their carbon structures called “saturated” because their carbon structures

are completely filled (saturated) with hydrogen are completely filled (saturated) with hydrogen atoms. atoms.

– chemical structure is very linear which allows for a chemical structure is very linear which allows for a “stacking” effect to occur. “stacking” effect to occur.

– stacking is what promotes the solidifying effect of stacking is what promotes the solidifying effect of most saturated fats (butter, lard, most animal fats). most saturated fats (butter, lard, most animal fats).

– solidification may also occur in the body which solidification may also occur in the body which partly explains the artery-clogging effects linked to partly explains the artery-clogging effects linked to saturated fats. saturated fats.

– Examples of saturated fats include myristic acid, Examples of saturated fats include myristic acid, palmitic acid, stearic acid, arachidic acid, and palmitic acid, stearic acid, arachidic acid, and lignoceric acid. These fats may raise cholesterol lignoceric acid. These fats may raise cholesterol levels in the body and should be used in levels in the body and should be used in moderationmoderation

Why are Why are trans- trans- fats bad?fats bad?

The The trans-trans- double bonds double bonds – Are more reactive in the bodyAre more reactive in the body

Promote free radical formation Promote free radical formation – Leads to destruction of biomoleculesLeads to destruction of biomolecules

– Are more likely to clog arteriesAre more likely to clog arteriesDue to shape, get caught in bodyDue to shape, get caught in body

– Promote cholesterol levels to increase, since they can Promote cholesterol levels to increase, since they can be used to make cholesterol in the bodybe used to make cholesterol in the body

– We don’t have the enzymes to process the We don’t have the enzymes to process the trans-trans- fats fats(we can process (we can process cis- cis- fats)fats)

http://www.nhlbi.nih.gov/chd/Tipsheets/images/satfatgraph.gifhttp://www.nhlbi.nih.gov/chd/Tipsheets/images/satfatgraph.gif

Good fat/ Bad Good fat/ Bad fat?fat?

Spider silk monomerSpider silk monomer

(amino acid)(amino acid)– Amino acid R Amino acid R

groupsgroups

Kevlar monomerKevlar monomer

SilkSilk

Silk and Silk and proteinsproteins

ViscosityViscosity

Viscosity is the resistance to flowViscosity is the resistance to flow– The greater the viscosity, the greater the The greater the viscosity, the greater the

resistance to flowresistance to flow– Determined:Determined:

How quickly a fluid flows through a tube under How quickly a fluid flows through a tube under gravitational force (slower= more viscous)gravitational force (slower= more viscous)

– Or byOr by

Determining rate at which steel sphere fall through Determining rate at which steel sphere fall through the liquid (more viscous= more slowly)the liquid (more viscous= more slowly)

– Changes as temperature changesChanges as temperature changes

What is surface tension?What is surface tension?

Resistance of a liquid to an increase in it’s Resistance of a liquid to an increase in it’s surface area surface area (Zumdahl)(Zumdahl)

Free energy per unit surface area Free energy per unit surface area (Tinoco, Sauer, Wang (Tinoco, Sauer, Wang

and Puglisi)and Puglisi)

– Force per unit length (mNmForce per unit length (mNm-1, -1, oror dyne/cm)dyne/cm)

Layman’s terms: How much something Layman’s terms: How much something spreads out on a surface spreads out on a surface – Beading up= high surface tensionBeading up= high surface tension– Spreading out= low surface tensionSpreading out= low surface tension

Surface Tension

http://home.earthlink.net/~dmocarski/chapters/chapter7/main.htm

(High surface tension) (Low surface tension)

•The molecules of water have more adhesion to the (polar) glass than to each other (cohesion);

•The Hg has more cohesive forces than attraction to the glass

• Cohesion: Molecules sticking (due to IMFs) to the same molecule in a pure compound

• Adhesion: Molecules sticking (due to IMFs) to other molecules adjacent to the pure compound – (not a mixture- at a surface

interface)

Wetting and DewettingWetting and Dewetting

http://www.mpikg-golm.mpg.de/gf/1

http://www.mpikg-golm.mpg.de/gf/1

Wetting is how water (in this case) adheres to Wetting is how water (in this case) adheres to a surface; when the surface tension is lowered, a surface; when the surface tension is lowered, the material becomes wetter. the material becomes wetter. Surface tension of water is 73 dyne/ cm; Surface tension of water is 73 dyne/ cm;

http://home.att.net/~larvalbugrex/striders.htmlhttp://home.att.net/~larvalbugrex/striders.html

Water droplet on lotus leaf, with adhering particles

What causes surface tension?What causes surface tension?

Surface tension is a result of the imbalance of Surface tension is a result of the imbalance of forces at the surface (or interface) forces at the surface (or interface)

http://www.kibron.com/Science/

http://home.earthlink.net/~dmocarski/chapters/chapter7/main.htm

Surface tension of…Surface tension of…   mNmmNm-1-1 Temperature (˚C)Temperature (˚C)

PlatinumPlatinum 18191819 200200

MercuryMercury 487487 1515

WaterWater 71.9771.97 2525

WaterWater 58.8558.85 100 (liquid)100 (liquid)

BenzeneBenzene 28.928.9 2020

Acetone Acetone 23.723.7 2020

n- Hexanen- Hexane 18.418.4 2020

Molten IronMolten Iron 1717 16001600

Silicon OilSilicon Oil 16.916.9 2525

NeonNeon 5.25.2 -247-247(Tinoco, Sauer, Wang, and Puglisi);

http://www.boldinventions.com/tsun_sim_2.html

Does temperature matter?Does temperature matter?

Yes- part of the reason Yes- part of the reason that we wash in warm that we wash in warm water (at times), not cold water (at times), not cold – the fabric gets “wetter”– the fabric gets “wetter”As temperature As temperature increases, surface increases, surface tension decreasestension decreases

(Surface tension given for (Surface tension given for water against air)water against air)

surface tension surface tension (mNm(mNm-1-1))

-8-8 7777

-5-5 76.476.4

00 75.675.6

55 74.974.9

1010 74.2274.22

1515 73.4973.49

1818 73.0573.05

2020 72.7572.75

2525 71.9771.97

3030 71.1871.18

4040 69.5669.56

5050 67.9167.91

6060 66.1866.18

7070 64.464.4

8080 62.662.6

100100 58.958.9

temperature ( C)temperature ( C)

http://scienceworld.wolfram.com/physics/SurfaceTension.html

Temperature and IMFsTemperature and IMFs

IMFs in a substance change in strength in IMFs in a substance change in strength in a substance as temperature changesa substance as temperature changesThis influences certain properties of the This influences certain properties of the substancessubstances– Surface tensionSurface tension– ViscosityViscosity– Capillary actionCapillary action– Vapor pressureVapor pressure(but not BP, MP)(but not BP, MP)

Capillary Action

http://home.earthlink.net/~dmocarski/chapters/chapter7/main.htm

•Capillary action: a phenomenon associated with surface tension and resulting in the elevation or depression of liquids in capillaries (from www.dictionary.com)

•The molecules of water have more adhesion to the (polar) glass than to each other (cohesion);

•The Hg has more cohesive forces than attraction to the glass

•(glass is polar)

Vaporization and Vapor PressureVaporization and Vapor Pressure

The molecules in a sample of a liquid The molecules in a sample of a liquid move at various speedsmove at various speeds– (average speed is the temperature; some (average speed is the temperature; some

have more energy, some have less, but the have more energy, some have less, but the overall KE is temperature)overall KE is temperature)

Sometimes molecules at the surface have Sometimes molecules at the surface have sufficient speed to overcome the attractive sufficient speed to overcome the attractive forces and leave the liquid surface (thus forces and leave the liquid surface (thus vaporizing)vaporizing)

Figure 14.9: Microscopic view Figure 14.9: Microscopic view of a liquid near its surface.of a liquid near its surface.

Dynamic equilibriumDynamic equilibriumDynamic equilibrium is the state where Dynamic equilibrium is the state where there is simultaneous and equal there is simultaneous and equal vaporization and condensation of the vaporization and condensation of the substancesubstance

In a closed container, at some pressure, In a closed container, at some pressure, the amount that vaporizes will equal the the amount that vaporizes will equal the amount condensing on the surface of the amount condensing on the surface of the liquidliquid– This is the equilibrium vapor pressureThis is the equilibrium vapor pressure

VP and IMFsVP and IMFsStronger IMFs equal lower vapor pressuresStronger IMFs equal lower vapor pressures– Less likely to evaporateLess likely to evaporate

Weaker IMFs equal higher vapor pressuresWeaker IMFs equal higher vapor pressures– Substance with very low IMFs and therefore Substance with very low IMFs and therefore

high vapor pressures evaporate very quickly high vapor pressures evaporate very quickly and easilyand easily

Called volatile substanceCalled volatile substance

Mass and shape important, just like with Mass and shape important, just like with boiling pointboiling point– Heavier = lower VPHeavier = lower VP

ex: oilex: oil– Lighter= higher VPLighter= higher VP

ex: alcoholex: alcoholMore volatileMore volatile

Think propane (CThink propane (C33HH88) v. gasoline (C) v. gasoline (C88HH1818))

VP and BoilingVP and Boiling

Vaporization occurs at any temperature, but Vaporization occurs at any temperature, but occurs more rapidly as temperature occurs more rapidly as temperature increasesincreases– Molecules at the surface would have to have Molecules at the surface would have to have

more speed to overcome the IMFsmore speed to overcome the IMFs– Boiling is the point at which the vapor pressure Boiling is the point at which the vapor pressure

equals the external pressure on the surface of equals the external pressure on the surface of the liquidthe liquid

Molecules are able to “escape” liquid phase b/c they Molecules are able to “escape” liquid phase b/c they have enough Energy to break the IMFshave enough Energy to break the IMFs

– Convert PE of IMFs to KE of motion in a gasConvert PE of IMFs to KE of motion in a gas

Boiling and VP, con’tBoiling and VP, con’t

Liquids have some air dissolved in them in tiny invisible bubbles Liquids have some air dissolved in them in tiny invisible bubbles As water vaporizes in the liquid, it is added to the bubblesAs water vaporizes in the liquid, it is added to the bubblesAlso, the gas bubbles are expanding because they are being Also, the gas bubbles are expanding because they are being heated; this causes an increase in volume, but not mass heated; this causes an increase in volume, but not mass – At this point, 2 things are going on:At this point, 2 things are going on:

This decreases density, causing the bubbles to float to the surfaceThis decreases density, causing the bubbles to float to the surfaceAlso, as gas expands, the pressure increasesAlso, as gas expands, the pressure increases

– When the pressure of the bubble increases to greater than the vapor pressure at the surface, the liquid is boiling

All molecules must be vaporized before a further increase in All molecules must be vaporized before a further increase in temperature can occurtemperature can occur– Need to break all IMFs (convert all PE of IMFs before increasing KE of Need to break all IMFs (convert all PE of IMFs before increasing KE of

molecules)molecules)

Boiling Point and ElevationBoiling Point and Elevation

As elevation on the Earth’s surface increases, As elevation on the Earth’s surface increases, the atmospheric pressure decreasesthe atmospheric pressure decreases– (smaller column of air pushing down on the area; (smaller column of air pushing down on the area;

therefore less pressure)therefore less pressure)

Boiling point changes as the atmospheric Boiling point changes as the atmospheric pressure changespressure changes

If you could decrease the pressure without If you could decrease the pressure without changing temperature, the substance would boil changing temperature, the substance would boil at a lower temperatureat a lower temperature– A decrease in pressure results in a decrease in BPA decrease in pressure results in a decrease in BP

Figure 14.14: The formation of the bubble is Figure 14.14: The formation of the bubble is opposed by atmospheric pressure.opposed by atmospheric pressure.

Energy Changes Accompanying Changes of State

Think back: Each change of state is accompanied by a change in the energy of the system– Whenever the change involves the disruption of intermolecular

forces, energy must be supplied

The disruption of intermolecular forces accompanies the state going towards a less ordered state (higher entropy)– As the strengths of the intermolecular forces increase, greater

amounts of energy are required to overcome them during a change in state

Takes more energy to go from – a liquid to a gas

than – from a solid to a liquid

Removing energy allows the molecules to “self- organize”, and results in an more ordered state– Lower entropy

Heat of FusionHeat of Fusion

The melting process for a solid is also referred to as fusion – The enthalpy change associated with

melting a solid is often called the heat of fusion (Δ Hfus)

Ice ΔHfus = 6.01 kJ/mol

– Δ H is a change (Δ) in enthalpy (H), a measure of energy that is much like heat, but takes into account a few other factors

Heat of VaporizationHeat of Vaporization

The heat needed for the vaporization of a liquid is called the heat of vaporization (Δ Hvap)

Water Δ Hvap = 40.67 kJ/mol

Vaporization requires the input of heat energy

Less energy is needed to allow molecules to move past each other than to separate them totally, – so ΔHfus < Δ Hvap

The heating/cooling curve for water heated or cooled at a constant rate.

Energy/ disorder diagramEnergy/ disorder diagram

Energy and IMFsEnergy and IMFs

Remember Remember Kinetic energy is the Energy associated with Kinetic energy is the Energy associated with moving particlesmoving particlesHeat is the Heat is the RANDOMRANDOM KE of an object KE of an object – (as opposed to directional motion)(as opposed to directional motion)

Temperature is the measure of the Temperature is the measure of the AVERAGEAVERAGE KE in a substanceKE in a substanceWhen IMFs are disturbed due to E changes, the When IMFs are disturbed due to E changes, the properties of the substance change, even to the properties of the substance change, even to the point of changing state because the PE of the point of changing state because the PE of the molecules changesmolecules changes

Think of IMFs like magnets: stronger Think of IMFs like magnets: stronger magnets hold things more firmly magnets hold things more firmly togethertogether– The more firm the connections, the less The more firm the connections, the less

molecular motion can occur with the molecular motion can occur with the same amount of Energy addedsame amount of Energy added

– Adding (or removing) energy from the Adding (or removing) energy from the system can overcome (or increase) the system can overcome (or increase) the IMFs, and cause a change in stateIMFs, and cause a change in state

Add Energy, move from S -> L -> GAdd Energy, move from S -> L -> G– Endothermic processEndothermic process

Remove Energy, move from G -> L -> SRemove Energy, move from G -> L -> S– Exothermic processExothermic process

Air conditioners Air conditioners take advantage take advantage of Energy of Energy changes to changes to remove heat remove heat energy from a energy from a warm indoor warm indoor environment by environment by vaporizing vaporizing condensed gascondensed gasOn the outdoor On the outdoor portion of the portion of the AC unit, the gas AC unit, the gas is condensed to is condensed to a liquid, sending a liquid, sending the heat energy the heat energy to the to the environmentenvironment

Phase DiagramPhase Diagram

Due to Due to changes in changes in pressure and pressure and temperature, temperature, a substance a substance can exist in can exist in all three all three states under states under specific specific conditions conditions – The Triple The Triple

Point Point Think Think foggy icy foggy icy daysdays

Explain how the lava lamp works (Explain how the lava lamp works (notnot “you “you plug it in”! On a molecular level, explain plug it in”! On a molecular level, explain what is happening to the materials and what is happening to the materials and their IMFs- this is beyond how we their IMFs- this is beyond how we answered this question earlier this year!)answered this question earlier this year!)