3.1.3 Bonding - Intermolecular Forces Flashcards
Which substances have intermolecular forces between molecules?
Simple molecules
Are intermolecular forces strong or weak?
Weak
What are the three types of intermolecular forces?
Hydrogen bonding, Permanent dipole-dipole, Induced dipole-dipole
Which is the strongest type of intermolecular force?
Hydrogen bonding
Which is the weakest type of intermolecular force?
Induced dipole-dipole
When is a molecule non-polar?
Molecule is symmetrical,
Dipoles cancel out
When is a molecule polar?
Molecule is not symmetrical.
Dipoles do not cancel out.
When substances with a simple molecular structure are melted or boiled what is broken?
Weak intermolecular forces are broken
Do simple molecules have a high melting point or a low melting point?
Low. The weak intermolecular forces between molecules are broken.
What is the strongest intermolecular force between polar molecules?
Permanent dipole-dipole
What is the strongest intermolecular force between non-polar molecules?
Induced dipole-dipole
What is the strongest type of intermolecular force between simple molecules that have a H bonded to an N, O or F?
Hydrogen bonding
How do you know if simple molecules have hydrogen bonding between them?
- They have a H bonded to an N, O or F.
- A lone pair of electrons on the fluorine, oxygen or nitrogen
Hydrogen bonding is the strongest type of intermolecular force, true or false?
True
Induced dipole-dipole is the weakest type of intermolecular force, true or false?
True
Explain how is an induced dipole-dipole intermolecular force is formed between 2 non-polar molecules.
- Random movement of electrons in one molecule (atom) leads to an…
Uneven distribution of electron, creating a… - Temporary dipole in one molecule (atom). This…
- Induces a dipole in a neighboring molecule (atom).
- Dipoles attract
If the strongest intermolecular force between molecules is Hydrogen bonding, which other intermolecular forces do they also have?
Permanent dipole-dipole and Induced dipole-dipole
If the strongest intermolecular force between molecules is permanent dipole-dipole, which other intermolecular force do they also have?
Induced dipole-dipole
Non-polar molecules only have induced dipole-dipole forces between molecules, true or false?
True
What increases the strength of induced dipole-dipole forces?
More electrons
More surface contact area
Which has stronger induced dipole-dipole, Cl2 or Br2 ?
Br2. It has more electrons
Which has stronger induced dipole-dipole, F2 or I2 ?
I2. It has more electrons
Which has stronger induced dipole-dipole, S8 or P4 ?
P4. Bigger molecules so has more electrons
Which has stronger induced dipole-dipole, C3H8 or C4H10?
C4H10. Bigger molecules so has more electrons
Which has a higher boiling point, Cl2 or Br2 ?
Br2. It has more electrons so stronger induced dipole-dipole.
Which has a higher boiling point, F2 or I2 ?
I2. It has more electrons so stronger induced dipole-dipole.
Is CCl4 polar or non-polar molecule? (Clue: Draw it out with partial charges.)
Non-polar
Symmetrical molecule
Dipoles cancel out
Is CHCl3 polar or non-polar molecule? (Clue: Draw it out with partial charges.
Polar
Not symmetrical molecule
Dipoles do not cancel out
Why does HBr have a higher boiling point than HCl?
Both polar molecules
Strongest intermolecular force is permanent dipole-dipole.
They will also have induced dipole-dipole.
HBr has more electrons that HCl, stronger induced dipole-dipole attraction.
Why does HI have a higher boiling point than HCl?
Both polar molecules
Strongest intermolecular force is permanent dipole-dipole.
It will also have induced dipole-dipole.
HI has more electrons that HCl, stronger induced dipole-dipole attraction.
Why does HI have a higher boiling point than HF?
Both polar molecules
Strongest intermolecular force is permanent dipole-dipole.
It will also have induced dipole-dipole.
HI has more electrons that HF, stronger induced dipole-dipole attraction.
Would the molecule be polar or non-polar if it is symmetrical and
dipoles cancel out?
Non-polar
Would the molecule be polar or non-polar if it is not symmetrical and
dipoles do not cancel out?
Polar
Which molecules would have a higher melting point?
Molecules with hydrogen bonding between molecules or
Molecules with Induced dipole-dipole forces between molecules.
Molecules with hydrogen bonding between molecules. Hydrogen bonding would require more energy to break the intermolecular forces.
Correct the following statement:
Simple molecules have low melting points as they have intermolecular forces which require less energy to break the bonds
Simple molecules have low melting points as they have intermolecular forces BETWEEN MOLECULES which require less energy to break the FORCES
Correct the following statements:
Cl2 has a lower boiling point than HF. Cl2 has induced dipole-dipole forces and HF has hydrogen bonding. induced dipole-dipole is weaker than hydrogen bonding. Less energy is require the break the bonds between Cl2.
Cl2 has a lower boiling point than HF. Cl2 has induced dipole-dipole forces between molecules and HF has hydrogen bonding between molecules. induced dipole-dipole forces are weaker than hydrogen bonding. Less energy is require the break the forces between Cl2.
How does permenant dipole-dipole arise
- Difference in electronegativity leads to bond polarity
Dipoles don’t cancel therefore the molecule has an overall permanent dipole - There is an attraction between ∂+ on one molecule and ∂− on another
