Unit 7.5 Comparing Intermolecular Forces
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Transcript of Unit 7.5 Comparing Intermolecular Forces
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Unit 7.5 Comparing Intermolecular Forces
Teacher: Dr. Van Der Sluys
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Objectives
• To determine– Relative melting and boiling points– Relative solubility of various combinations
of compounds
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Vocabulary
• Solution - a homogeneous mixture of two or more compounds.
• Solvent - The compound that comprises the majority of a solution.
• Solute - A minor component of a solution.
• Aqueous solution - A mixture of liquid water and one or more solutes.
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Types of BondingIntramolecular Intermolecular
Nonpolar Covalent London Dispersion Forces
Polar CovalentLondon Dispersion when symmetric
Dipole-Dipole when asymmetric
Extremely Polar Covalent: H-N,
H-O or H-F bondsHydrogen Bonding
Weakly Ionic:
NaCl
Soluble in water due to
ion-dipole interactions
Extremely Ionic:
Fe2O3
Insoluble in water due to high crystal lattice energies
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Like Dissolves Like
• In order for a mixture to combine and become homogeneous on the molecular level, the compounds must have similar intermolecular bonding properties, i.e. ethanol and water.
• Two compounds that have very different intermolecular forces will not mix and will produce a heterogeneous mixture, i.e. Italian salad dressing.
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Comparing Intermolecular Forces
Compound London Dispersion
Dipole-Dipole
(AXE?)
Hydrogen Bonding
(H-F, H-N, H-O)
Weakly Ionic
(Ions with low
charges)
Strongly ionic
(Both ions have
charges >2
Usually Insoluble in
H2O)
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Comparing Intermolecular Forces
Compound London Dispersion
Dipole-Dipole
(AXE?)
Hydrogen Bonding
(H-F, H-N, H-O)
Weakly Ionic
(Ions with low
charges)
Strongly ionic
(Both ions have
charges >2
Usually Insoluble in
H2O)
CH4
methane
H2O
water
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Comparing Intermolecular Forces
Compound London Dispersion
Dipole-Dipole
(AXE?)
Hydrogen Bonding
(H-F, H-N, H-O)
Weakly Ionic
(Ions with low
charges)
Strongly ionic
(Both ions have
charges >2
Usually Insoluble in
H2O)
NH3
ammonia
H2O
water
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Comparing Intermolecular Forces
Compound London Dispersion
Dipole-Dipole
(AXE?)
Hydrogen Bonding
(H-F, H-N, H-O)
Weakly Ionic
(Ions with low
charges)
Strongly ionic
(Both ions have
charges >2
Usually Insoluble in
H2O)
Fe2O3
Iron(III) oxide
C8H18
octane
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Comparing Intermolecular Forces
Compound London Dispersion
Dipole-Dipole
(AXE?)
Hydrogen Bonding
(H-F, H-N, H-O)
Weakly Ionic
(Ions with low
charges)
Strongly ionic
(Both ions have
charges >2
Usually Insoluble in
H2O)
CO2
Carbon dioxide
H2O
water
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Melting and Boiling Points
• The relative melting and boiling of various compounds are due to the strength of intermolecular forces.
• If two compounds have the same types of intermolecular forces, the total number of electrons can usually be used to predict the degree of London dispersion forces. The compound with more electrons usually has the higher melting and boiling points.
• For compounds with hydrogen bonding, the ratio of hydrogen atoms to lone pairs can be important.
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Comparing Intermolecular Forces
Compound
London Dispersion
(Total number of electrons?)
Dipole-Dipole
(AXE?)
Hydrogen Bonding
(H-F, H-N, H-O)
Weakly Ionic
(Ions with low
charges)
Strongly ionic
(Both ions have
charges >2
Usually Insoluble in
H2O)
CH4
methane
C2H6
ethane
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Comparing Intermolecular Forces
Compound
London Dispersion
(Total number of electrons?)
Dipole-Dipole
(AXE?)
Hydrogen Bonding
(H-F, H-N, H-O)
Weakly Ionic
(Ions with low
charges)
Strongly ionic
(Both ions have
charges >2
Usually Insoluble in
H2O)
CO2
Carbon dioxide
H2O
water
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Comparing Intermolecular Forces
Compound
London Dispersion
(Total number of electrons?)
Dipole-Dipole
(AXE?)
Hydrogen Bonding
(H-F, H-N, H-O)
Weakly Ionic
(Ions with low
charges)
Strongly ionic
(Both ions have
charges >2
Usually Insoluble in
H2O)
NaClSodium chloride
C6H14
Hexane
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Comparing Intermolecular Forces
Compound
London Dispersion
(Total number of electrons?)
Dipole-Dipole
(AXE?)
Hydrogen Bonding
(H-F, H-N, H-O)
Weakly Ionic
(Ions with low
charges)
Strongly ionic
(Both ions have
charges >2
Usually Insoluble in
H2O)
CO2
Carbon dioxide
H2O
water
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Summary
• If compounds have similar intermolecular forces they tend to form homogeneous solutions, “like dissolves like.”
• The strength of intermolecular forces can be used to predict relative melting and boiling points