CHEM 112 - MIDTERM I Flashcards
Between dispersion forces, dipole-dipole, and hydrogen bonding, which one is the strongest intermolecular force?
Hydrogen bonding
What are intermolecular forces?
Noncovalent interactions
What are the intermolecular forces?
Dispersion forces
Dipole-dipole force
Hydrogen bonding
Ion-dipole
Ionic bonding
Why are intermolecular forces critical to enzyme function?
Hydrogen bonding and ion-dipole interactions stabilize the enzyme structure
Intermolecular forces are ____ than intramolecular forces
weaker
Intermolecular forces are interactions ____ molecules
between
What is the weakest of all intermolecular forces?
Dispersion forces
What are dispersion forces?
Result from the attraction of instantaneous partial positive and negative charges across molecules; they arise from temporary dipoles induced in atoms or molecules
What are dispersion forces?
Result from the attraction of instantaneous partial positive and negative charges across molecules; they arise from temporary dipoles induced in atoms or molecules
How are dispersion forces present between two Helium atoms?
They promote attractive interactions between induced partial positive charge in one He atom with the induced negative charge with the second He atom to form an overall neutral charge
How are the temporary partial positive and negative charges between electrons produced?
Asymmetric electron placement in the electron cloud via instantaneous dipole moments
How do dispersion forces present in heavier molecules?
Dispersion forces are stronger in heavier molecules because they have more electrons that can asymmetrical distributed to produce temporary dipoles
Between He and Xe, which atom has stronger dispersion forces?
Xe - because it has more electrons
Molecules experiencing stronger dispersion forces have _____ boiling points
Higher
Which halogen will have the highest boiling point: Cl2 or Br2 or I2?
I2 - it is the largest halogen in the group and has the most electrons (requires more energy to break the bond)
Place the following compounds in order of increasing strength of intermolecular forces: CH4, CH3CH2CH3, CH3CH3
CH4 < CH3CH3 < CH3CH2CH3
CH3CH2CH3 has the most atoms with the most electrons - will have the strongest dispersion force and highest boiling point
What are dipole-dipole forces?
Attractive interactions between polar molecules
Why are dipole-dipole forces stronger than dispersion forces?
The partial charges in molecules are greater than dispersion forces (and achieve dipole moments)
Molecules with ____ polarity have stronger dipole-dipole forces
greater (because they have more significant partial positive and partial negative charges)
Which molecule would have stronger dipole interactions: CH3Cl or CH2Cl2?
CH2CL2 will have stronger dipole interactions because Cl-C-Cl bonding will promote a stronger dipole moment than just C-Cl bonding
A molecule that has dipole-dipole forces must also have what?
Dispersion forces
Dispersion forces are ____ than dipole-dipole forces
Weaker
Do dipole-dipole forces occur in nonpolar molecules?
NO - must have at least one polar molecule
Do dipole-dipole forces occur in polar molecules?
YES - duh