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: