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Keith Warne Keith Warne TeachBomb www.TeachBomb.com Keith Warne Keith Warne TeachBomb www.TeachBomb.com Intermolecular Forces Keith Warne www.TeachBomb.com.

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Presentation on theme: "Keith Warne Keith Warne TeachBomb www.TeachBomb.com Keith Warne Keith Warne TeachBomb www.TeachBomb.com Intermolecular Forces Keith Warne www.TeachBomb.com."— Presentation transcript:

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2 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb Intermolecular Forces Keith Warne O ++ -- H H O ++ -- H H Intermolecular Intramolecular Intermolecular Forces

3 Dissolution of a salt

4 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb Solubility Investigate 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. SOLUBILITY WaterHexaneEthanol I2I2 KMnO 4 Work through this presentation on intermolecular forces and the one on Bonding & Structure and try to find explanations for the above observations! Try and work out some simple solubility rules consistent with your investigation.

5 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb 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 USE ARROWS TO INDICATE THE TWO TYPES OF BONDS IN THE DIAGRAM Intermolecular forces O ++ -- H H O ++ --HH Intermolecular ?? Intramolecular ??

6 Bond Polarity in Water The oxygen atom has greater electronegativity than the hydrogen atoms so oxygen attracts the bonding electrons (shared pairs) closer to itself. -- ++ O HH HH DIPOLE The water molecule is therefore a DIPOLE - it has two oppositely charged “poles”. We say water is a polar compound. Electrons attracted closer to oxygen Lewis diagram Space filled model  = small charge created by unequally shared electrons

7 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb 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- NX 2 or H-F. (X = any atoms) These bonds result in abnormally high boiling points. USE DOTTED LINES TO SHOW WHERE HYDROGEN BONDS WOULD BE FOUND IN THE DIAGRAM Hydrogen Bonds O ++ -- H H O ++ --HH O ++ -- H H Example: Water Other Examples??

8 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb Hydrogen Bonding

9 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. public domain Materialscientistwikipedia Materialscientist Hydrogen Bonding in Ice Label the oxgen and hydrogen atoms in the diagram and indicate the hydrogen bonds. licence behind image

10 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb Ion - dipole forces- arise from the electrostatic attraction between an ion and the oppositely charged pole of a polar molecule Shown in diagram by dotted lines. What type of substances (solutes & solvents) would display this type of forces?). Ion-Dipole Forces O ++ -- H H O ++ -- H H Example:???? O ++ -- H H

11 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb Ion-induced Dipole Attractive force between ions and weak dipoles which are induced (caused) in non polar molecules This happens when an ion comes close to a non polar molecule. (Polarisation) It occurs between ionic substances and non polar solvents. SHOW THE DIRECTION THE ELECTRONS HAVE MOVED USING ALSO INDICATE THE RESULTING POLARITY ON THE MOLECULE Example:???? Cl - Non-polarMolecule Ion Induced dipole?

12 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb Dipole - Dipole Forces Attractive forces that exist between molecules that have permanent dipoles. These exist in any polar substance. In order to create a dipole or polar molecule, the molecule must have: –………………….. Determine which of the following would exhibit Dipole Dipole forces H 2 S, CO 2, C 2 H 4 give a reason in each case. Exampes:???? H Cl ++ -- H Cl ++ -- dipole dipole Attractive force

13 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb London Forces A temporary dipole is induced in a non polar molecule due to electron movements. These INDUCE similar but opposite forces in neighboring molecules which cause weak momentary attractions. These are the WEAKEST attractive forces that exist between molecules. How would the strength of London forces be affected by the size of the molecule?? Example:……………..  Electrons repelled Temporary dipole Induced dipole Electrons moving Weak short lived attraction

14 BOND STRENGTH Melting/Boiling Points INCREASE Intermolecular Forces Hydrogen Bonds Ion-dipole Ion-induced Dipole Van der Waals Forces Forces Dipole-dipole Dipole-inducedDipole Momentary Dipole (London) Viscosity INCREASE CONSTRUCT A FLOW CHART WHICH CONNECTS ALL THE INTERMOLECULAR FORCES AND SHOWS THEIR RELATIONSHIPS

15 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb Dissolution (dissolving) Salt (NaCl) dissolves in water spontaneously. Since water is a molecule it can be represented as a dipole (two oppositely charged poles) ---- ++++ Cl - Na + ---- ++++ ---- ++++ The charged ends of the dipole would be attracted to the charge on the ionic solid. O H H   `

16 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb The dissolution process Solvent molecules (water) are attracted to the solute particles as they have forces of attraction between them. Solvent: water bonding (electrostatic forces - strong) Cl - ---- ++++ ---- ++++ ---- ++++ Na + ---- ++++ ---- ++++ ---- ++++ Cl - Na + Solute: Sodium Chloride bonds strong electrostatic attraction of oppositely charged ions. Since the forces in the SOLVENT are similar to those in the SOLUTE the solvent particles are able to substitute for and break up the forces in the solute material - which is then literally ripped apart!

17 Molecular solids Iodine - I 2 Strong covalent bonds Weaker intermolecular bonds – London forces (between molecules) Covalently bonded molecules held together by weaker intermolecular bonding. PROPERTIES melting points Soluble in solvents ( – conducting) unit-cell-3D-balls-B.png

18 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb Solubility WaterParrafinEthanol I2I2 KMnO 4 Explain the solubility's you have observed i.t.o intermolecular bonding.

19 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb Vapour Pressure The vapor pressure of a liquid is the equilibrium of a vapor above its liquid (or solid. Liquids boil when their vapour pressure the atmospheric pressure. There is a relationship between intermolecular force strength and vapour pressure. substance vapor pressure at 25 o C diethyl ether0.7 atm bromine0.3 atm ethyl alcohol0.08 atm water0.03 atm Low Vp Higher Vp Vapour pressure is inversely proportional to intermolecular bond strength: STRONGER IMF = LOWER Vp Stronger IMF Weaker IMF

20 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb Density Density = mass/volume (g.cm -3 ) density – solids particles per cm IMF density – gases particles per cm IMF IMF 1cm x 1cm x 1cm = 1cm 3 bon-dioxide-crystal-3D-vdW.png etic_theory_of_gases.svg

21 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb Permission requested: Viscosity Viscosity is a measure of how thick (viscous) and sticky a liquid is.Viscosity is a measure of how thick (viscous) and sticky a liquid is. Viscosity reduces the ability of a liquid to flow.Viscosity reduces the ability of a liquid to flow. Liquids that flow readily (water) have a low viscosity.Liquids that flow readily (water) have a low viscosity. Viscosity is a function of (depends on) the attractive forces of the molecules of the liquid.Viscosity is a function of (depends on) the attractive forces of the molecules of the liquid. Strong forces – high viscosityStrong forces – high viscosity Temperature also greatly affects viscosity: as temperature increases, viscosity decreases.Temperature also greatly affects viscosity: as temperature increases, viscosity decreases. Kinetic energy enables particles to overcome forces. Permission needed from: smartsynthetics.com

22 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb Iodine (solid) dissolves in hexane I 2 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.

23 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb Iodine + Water Iodine 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 (H 2 O) and solute particles (I 2 ). Dipole - induced dipole forces exist between water and iodine molecules.

24 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb KMnO 4 + Water Potassium permanganate is very soluble in water. KMnO 4 is an ionic substance. Water contains hydrogen bonds, ION - DIPOLE FORCES EXSIST between these two substances. These are relatively strong intermolecular forces and that accounts for the solubility of ionic substances in polar solvents.

25 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb KMnO 4 + Hexane Potassium permanganate is insoluble in hexane. KMnO 4 is an ionic substanceKMnO 4 is an ionic substance Hexane is non-polar - v.d. Waals (london) forcesHexane is non-polar - v.d. Waals (london) forces Ion - induced dipole forces would exist between solvent molecules - these are VERY weak interactionsIon - induced dipole forces would exist between solvent molecules - these are VERY weak interactions The solubility is VERY LOW.The solubility is VERY LOW.

26 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb Ethanol + Iodine Iodine is soluble in Ethanol (C 2 H 5 OH) INTERMOLECULAR FORCES Ethanol + KMnO 4 Potassium permanganate is soluble in Ethanol (C 2 H 5 OH).

27 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb Ethanol + Iodine Iodine is soluble in Ethanol (C 2 H 5 OH) INTERMOLECULAR FORCES Iodine - v.d. Waals (London) forcesIodine - v.d. Waals (London) forces Ethanol - hydrogen bonds and london forcesEthanol - hydrogen bonds and london forces Dipole - induced dipole forces would exist between solvent and solute as well as v.d.Waals (London) forcesDipole - induced dipole forces would exist between solvent and solute as well as v.d.Waals (London) forces The london forces between ethanol molecules could be substituted for london forces in the iodine and so iodine is soluble in ethanol.The london forces between ethanol molecules could be substituted for london forces in the iodine and so iodine is soluble in ethanol. Ethanol + KMnO 4 Potassium permanganate is soluble in Ethanol (C 2 H 5 OH). The ion-dipole interactions between KMnO 4 and ethanol molecules are strong enough to cause dissolution of the ionic salt.

28 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb Solubility Rules Polar solutes will be soluble in ………………solvents.Polar solutes will be soluble in ………………solvents. Non-polar solutes will be soluble in …………… solvents.Non-polar solutes will be soluble in …………… solvents. Non-polar solutes will NOT be soluble in ………... solvents.Non-polar solutes will NOT be soluble in ………... solvents. Polar solutes will NOT be soluble in ………………. solvents.Polar solutes will NOT be soluble in ………………. solvents.…………………………………….

29 Keith Warne Keith Warne TeachBomb Keith Warne Keith Warne TeachBomb


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