Catalyst
End
How To Approach FRQ
1.
2.
3.
4.
Write down everything the problem gives you
Identify what the question wants you to find
Lay out a path to solve the problem
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 Time
• Read 11.1 – 11.3 and answer the essential
questions
• Do book problems: