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Catalyst
End
How To Approach FRQ1. Write down everything the problem
gives you2. Identify what the question wants you to
find3. Lay out a path to solve the problem4. Solve
Free Response Practice
Intermolecular Investigation•With your partners, complete the handout
“Intermolecular Investigation”•Be sure to answer the questions when
complete
Lecture 4.5 – Solids, Liquids, and Intermolecular Forces
Today’s Learning Targets• LT 4.8 – Using the kinetic molecular theory, I can
explain the movement of atoms in liquids and solids.• LT 4.10 – I can compare and contrast the three types
of intermolecular forces (Van der Waals, dispersion, and hydrogen bonding), identify the types in a given solution, and analyze chemical properties that result because of these forces.
Kinetic Molecular Theory: Solids and Liquids
•Recall, KMT states we can ignore the attractive forces between molecules in the gas phase.
•We cannot ignore these forces in solids/liquids
•As molecules cool, kinetic energy decreases and intermolecular forces increase
Intermolecular Forces• Intermolecular Forces are the forces that
exist between molecules• Much weaker than ionic, covalent, and
metallic forces• Many properties result because of it
Dispersion/London Forces• In an neutral atom, electrons are spread evenly
throughout a molecule• When two molecules are brought close enough
to one another, electrons rearrange to create a temporary dipole
• The greater the polarizability of the molecule determines the strength of the dispersion force▫Increase as the molecular weight increases
Dipole – Dipole Forces•When a molecule has a permanent dipole,
it has attractive forces to other dipoles•Dipole – Dipole Forces are the
attractive forces between molecules with partial positive and partial negative charges.
•The larger the molecular weight, the larger the dipole – dipole force
Hydrogen Bonding • When H bonds to N, O, or F, there is a huge
difference in electronegativity• Hydrogen bonding is the intermolecular
force between the hydrogen bound to N, O, or F and another N, O, or F atom.
• Type of dipole – dipole interaction
Ion – Dipole Forces•When we have a polar molecule, it can
also be attracted to an ion.•This is an ion – dipole force
Identifying Forces in Molecules• All molecules have London/dispersion forces
▫Larger molecules have larger dispersion forces
• The general strength of forces in molecules is:
Dispersion < Dipole – Dipole < Hydrogen Bonding < Ion - Dipole
Class Example•List the substance in order of increasing
intermolecular forces: BaCl2, H2, CO, HF, and Ne.
Table Talk•Order the molecules in order of
increasing intermolecular forces CH3CH3, CH3OH, CH3CH2OH
Properties From Intermolecular Forces: Boiling Point/Melting Point• The boiling point and melting point are
dependent upon the amount of intermolecular forces
• The more forces, the higher the boiling point and melting point because the molecules feel a greater attraction to one another.
• This means more energy is necessary so that these forces can be broken.
Properties From Intermolecular Forces: Viscosity• Viscosity is the resistance of a liquid to flow.• The more intermolecular forces, the higher
the viscosity of the material
Meet the Jesus Lizard
Properties From Intermolecular Forces: Surface Tension•Surface Tension is the measure of the
force it takes to break the surface of a given liquid
•The more forces, the greater the surface tension due to the extensive intermolecular bonding
Table Talk•Order the following molecules from
lowest to highest boiling points: CH3CH2OH, CH3CH2CH2OH, CH3CH2CH2CH2OH, and HOCH2CH2OH
Relay Races
Relay Race Questions•What are the intermolecular forces present in
SO2?•What are the intermolecular forces present in
CH3COOH?•What are the intermolecular forces present in
H2S?•Which substance has a larger dispersion
force: H2S or H2O?•Which molecule has more forces: HF or C2H6?
Closing TimeClosing Time•Read 11.1 – 11.3 and answer the essential
questions•Do book problems: