SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe Intermolecular Intermolecular Forces Forces Keith Warne Keith Warne www. www. sciencecafe sciencecafe .org.za .org.za O O + - H H H H O O + - H H H H Inter Inter molecular molecular Intra Intra molecular molecular Intermolecular Forces Intermolecular Forces
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Intermolecular ForcesIntermolecular Forces
Keith WarneKeith Warnewww.www.sciencecafesciencecafe.org.za.org.za
OO+
-HH
HH
OO+
-
HH
HHInterIntermolecular
molecular
IntraIntramolecu
lar
molecular
Intermolecular ForcesIntermolecular Forces
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SolubilityInvestigate the solubility's of the following solids in each of the liquids that follow. Use small quantities of each and
mix them together in a testube. Note down whether they are soluble, insoluble or slightly soluble.
SOLUBILITYWaterPolar
HexaneNon Polar
EthanolP & N.P
I2
Non Polar
Insoluble Soluble soluble
KMnO4
Ionic Soluble Insoluble/v
slightly soluble
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• Two different types of bonds occur in substances.
• Intramolecular– Between hydrogen atoms
and oxygen atoms inside the molecules Covalent bonds
• Intermolecular– Between two different water
molecules Hydrogen bonds
Intermolecular forces
OO+
-HH
HH
OO+ -HH
HHInterIntermolecular
molecular
IntraIntramolecular
molecular
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Bond Polarity in WaterThe oxygen atom has greater electronegativity than the hydrogen atoms so oxygen attracts the bonding electrons (shared pairs) closer to itself.
-+ OOHH
HH
The water molecule is therefore a DIPOLEDIPOLE - it has two oppositely charged “poles”. We say water is a polar compound.
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• The positive and negative atoms on each of the water molecules attract each other.
• This electrostatic attraction is called Hydrogen bonding.
• It is the strongest form of intermolecular attraction.
• Hydrogen bonding exists only between molecules in which hydrogen is bonded to a very electronegative atom H-O-X, H-NX2 or H-F. (X = any atoms)
• These bonds result in abnormally high boiling points.
• USE THE DOTTED LINES BELOW TO SHOW WHERE HYDROGEN BONDS WOULD BE FOUND IN THE DIAGRAM (7 Bonds)
Hydrogen Bonds
OO+
-HH
HHOO+ -
HH
HH
OO+
-
HH
HH
Example:Example:Water
Other Other Examples:Examples:HF, NHHF, NH3 3 any any alcohol CHalcohol CH33OH OH etc.etc.
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Hydrogen BondingWhere would you expect the next Where would you expect the next boiling points to be? (Hboiling points to be? (H22O, HF, NHO, HF, NH33))
TRENDTREND
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This work has been released into the public domain by its author, Materialscientist at the wikipedia project. This applies worldwide.In case this is not legally possible:Materialscientist grants anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law.
Hydrogen Bonding in Ice
Label the Label the oxgen and oxgen and hydrogen hydrogen atoms in the atoms in the diagram and diagram and indicate the indicate the hydrogen hydrogen bonds.bonds.
CONSTRUCT A FLOW CONSTRUCT A FLOW CHART WHICH CHART WHICH
CONNECTS ALL THE CONNECTS ALL THE INTERMOLECULAR INTERMOLECULAR
FORCES AND SHOWS FORCES AND SHOWS THEIR RELATIONSHIPSTHEIR RELATIONSHIPS
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Dissolution (dissolving)Salt (NaCl) dissolves in water
spontaneously.
Since water is a .................. molecule it can be represented as a dipole (two oppositely charged poles)
--++
ClCl--NaNa++--++
--++The The charged endscharged ends of the dipole would of the dipole would be be attractedattracted to the to the ................ ................ charge on the ionic solid.charge on the ionic solid.
O
H
H
`̀
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The dissolution processSolvent molecules (water)
are attracted to the solute particles as they have ......................... forces of attraction between them.
Solvent: water -....................... bonding (electrostatic forces - strong)
Since the Since the forces in the SOLVENT are similarforces in the SOLVENT are similar to those in to those in the the SOLUTESOLUTE the solvent particles are able to substitute the solvent particles are able to substitute for and break up the forcesfor and break up the forces in the in the solutesolute material - which material - which is then literally is then literally ripped apart!ripped apart!
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Molecular solids
Iodine - I2
Strong covalent bonds
Weaker intermolecular bonds – London forces (between molecules)
Covalently bonded molecules held together by weaker intermolecular
Viscosity• Viscosity is a measure of how Viscosity is a measure of how
thick (viscous) and sticky a thick (viscous) and sticky a liquid is. liquid is.
• Viscosity reduces the ability Viscosity reduces the ability of a liquid to flow. of a liquid to flow.
• Liquids that flow readily Liquids that flow readily (water) have a low viscosity. (water) have a low viscosity.
• Viscosity is a function of Viscosity is a function of (depends on) the attractive (depends on) the attractive forces of the molecules of the forces of the molecules of the liquid.liquid.
• Strong forces – high Strong forces – high viscosityviscosity
• Temperature also greatly Temperature also greatly affects viscosity: as affects viscosity: as temperature increases, temperature increases, viscosity decreases.viscosity decreases.
Kinetic energy enables particles to overcome forces.Kinetic energy enables particles to overcome forces.
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Iodine (solid) dissolves in hexane• I2 and hexane both have london forces between their
molecules• These forces are similar in strength and iodine
molecules can substitute hexane molecules in the solution
• Dissolution can take place.
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Iodine + WaterIodine is only sparingly soluble in water?
• Water contains hydrogen bonds, • iodine contains london forces.• The bonds have very different strengths.• Iodine molecules can not substitute for water
molecules in the solution - there is very weak attraction between the solvent particles (H2O) and solute particles (I2).
• Dipole - induced dipole forces exist between water and iodine molecules.
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Ethanol + IodineIodine is soluble in Ethanol (CIodine is soluble in Ethanol (C22HH55OH)OH)INTERMOLECULAR FORCESINTERMOLECULAR FORCES
Ethanol + KMnO4Potassium permanganate is soluble in Ethanol (CPotassium permanganate is soluble in Ethanol (C22HH55OH). OH).
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Solubility Rules• PolarPolar solutes will be soluble in solutes will be soluble in ………………………………solvents.solvents.
• Non-polarNon-polar solutes will be soluble in solutes will be soluble in ………………………… solvents. solvents.
• Non-polarNon-polar solutes will NOT be soluble in solutes will NOT be soluble in ………... ………... solvents.solvents.
• Polar solutesPolar solutes will NOT be soluble in will NOT be soluble in ……………….………………. solvents.solvents.
…………………………………………………………………………..
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