Correct or incorrect?
Raise the appropriate card at the count of three!
Intro questions – Correct or incorrect?
Intermolecular forces from strongest to weakest:
Hydrogen bonds – Dipole-Dipole forces – Van-der-Waals forces
Correct
Intro questions – Correct or incorrect?
A molecule that features polar bonds will have partial positive charges as well as partial negative charges. This type of molecule is called a
dipole molecule and can form dipole-dipole forces.
Incorrect
Intro questions – Correct or incorrect?
A molecule that features polar bonds will have partial positive charges as well as partial negative charges. If the positive and negative partial charges do not cancel out, this type of molecule is called a dipole
molecule and can form dipole-dipole forces.
Intro questions – Correct or incorrect?
Hydrogen bonds require a lone electron pair of a N, O or F-Atom with a positive partial charge as well as a hydrogen atom that is connected to a N, O or F-Atom
Incorrect
Intro questions – Correct or incorrect?
Hydrogen bonds require a lone electron pair of a N, O or F-Atom with a negative partial charge as well as a hydrogen atom that is connected to a N, O or F-Atom
Intro questions – Correct or incorrect?
Hydrogen bonds are similar to covalent bonds, only that they can only form between certain atom types.
Incorrect
Intro questions – Correct or incorrect?
Hydrogen bonds are not bonds but a type of intermolecular force. They are much weaker than covalent bonds and exist in between different molecules. Covalent bonds exist between the atoms within a molecule.
Intro questions – Correct or incorrect?
These two molecules can form hydrogen bonds
Correct
Intro questions – Correct or incorrect?
These two molecules can form hydrogen bonds
Correct
Intro questions – Correct or incorrect?
These two molecules can form hydrogen bonds:
Incorrect
Intro questions – Correct or incorrect?
These two molecules cannot form hydrogen bonds, there is no hydrogen atom connected to N, O or F:
Intro questions – Correct or incorrect?
These two molecules can form hydrogen bonds
Correct
Intro questions – Correct or incorrect?
These two molecules can form hydrogen bonds
Correct
Intro questions – Correct or incorrect?
Even though the molecule contains a hydroxyl group, 1-octanol is a non-polar substance.
Correct
Intro questions – Correct or incorrect?
Even though the molecule contains a hydroxyl group, 1-octanol is a non-polar substance. The non-polar part outweighs the polar part.
Correct
Today‘s topics
• Why do oil and water not mix?
Intermolecular forces and their effect
on substance properties
But first...
• Let‘s take a look at last weeks‘ experiment
In conclusion
• The more options a molecule has to form hydrogen bonds (partially negatively charged N,O,F-Atoms; H-Atoms bonded with N,O,F) the stronger the intermolecular forces in the substance will be.
• Higher melting and boiling points
• Higher viscosity as a liquid
So why do water and oil not mix?!
Let‘s explore this in a mini-experiment!
- You have six liquid substances: water, heptane, propan-1,2,3-ol (glycerine), oil, cleaning petroleum, ammonia (in fume cabinet).
- Research question: How do molecular properties influence how substances mix?
- Record the method, observations and conclusion (use internet research if you are unclear what the molecules involved look like) in a complete lab report.
- Have the completed lab report done and handed in by March 16th (that‘s the Friday before the school Saturday). You‘ll be graded!
- You have 45 Minutes time to collect your data and clean up! Work together as a desk-team!
- Use small amounts (1 ml max!). Everything containing heptane, petroleum or ammonia goes into the waste beaker!
Preliminary results
• The substances that were able to form hydrogen bonds (water, glycerine, ammonia) mixed well with each other but not with oil, heptane and
petroleum
• Heptane, which only forms Van-der-Waals forces, oil and petroleum mix well with each other
• Presumably oil and petroleum can only form Van-der-Waals forces as well
• Substances that share the same predominant intermolecular forces can be mixed!
Like mixes with like
2.4 Influence of intermolecular forces on substance properties
The dominating type of intermolecular force (Van-der-Waals Forces or Dipole-Dipole Forces incl. Hydrogen Bonds) that a molecule can form determines many substance properties, especially solubility.
Substances that share the same predominant intermolecular forces form homogeneous solutions. Substances that differ in this aspect cannot be mixed and form separate phases.
Task:
The terms lipophilic (fat loving), lipophobic (fat hating), hydrophilic (water loving) and hydrophobic (water hating) are often used when describing the solubility of a substance.
Arrage the terms into pairs that have the same meaning and explain the chemical background behind the terms.
Non-polar substances (VdWF predominant) are often referred to as lipophilic (fat loving) or hydrophobic (water hating). Polar substances (DDF predominant) are often referred to as lipophobic or hydrophilic.
