Module 4: Intermolecular Forces

Question 1

what are some applications of intermolecular forces?

Answer 1

surface tension (ex: water beads on a freshly waxed car)

capillary action (ex: finger prick blood with cylindrical tube)

viscosity: honey, syrup, motor oil

receptor drug binding
phase changes
solubility

Question 2

differentiate inTRAmolecular forces vs inTERmolecular forces

Answer 2

intTRA: within
ex) bonds between atoms of the same compound – C-C, or H-H
inTER: between
ex) bonds between compounds – forces between 2 H2O molecules (H2O and H2O)

Question 3

cohesive vs adhesive

Answer 3

cohesive: holds liquid molecules TOGETHER

adhesive: attraction of the OUTER molecules to the container’s surface

Question 4

what is viscosity?

Answer 4

the measure of a liquid’s resistance to flow

the amount of energy necessary to move an object through a fluid

the more viscous, the greater resistance

Question 5

what force of attraction is stronger? inter- or intramolecular forces?

Answer 5

intra > inter

intra: ionic, covalent, metallic bond

Question 6

what is an “electric dipole” or a “dipole moment”

Answer 6

the difference in EN (the sharing and shifting of electron density) between two atoms

ex) H-F where H has a lower EN and F has a higher EN
denoted by delta+ or delta- above the atom

Question 7

how to the vast majority of drug compounds bind to receptors?

Answer 7

intermolecular forces
(a small portion will bind via chemical bonding)

Question 8

how do intermolecular forces play a role in phase changes?

Answer 8

intermolecular forces need to be disrupted in order to phase change a substance
+ENERGY required

no bonds are broken
i.e.) frozen water and liquid water are the same compound

Question 9

give examples of non-polar dipole moments

Answer 9

C-C
H-H
C-H*
(any two of the same atoms)

these atoms do not have large difference in EN

non-polar: <0.5 EN

Question 10

give examples of polar dipole moments

Answer 10

C-O
C-N
C-S
P-O
N-H

polar: EN=0.5-1

Question 11

what is solubility?

Answer 11

attractive forces betwen solute and solvents

“like dissolves like” - components that have similar intermolecular forces will dissolve each other; dissimilar intermolecular forces do not dissolve

ex) non-polar + polar (repulsive forces); water + oil do not mex

ex)

Question 12

in order to have an intermolecular force, there has to be a ____ between compounds

Answer 12

“closeness”

Question 13

list the 5 intermolecular forces from weakest to strongest

Answer 13

1. van der Waals (London Dispersion) forces
2. dipole-dipole interactions
3. H bonding
4. ion-dipole
5. electrostatic interactions (ion-ion)

INTRA:
covalent bonds

Question 14

what is surface tension?

Answer 14

the liquid’s resistance to increase its surface area

Question 15

van der Waals forces
(London Dispersion)

Answer 15

between 2 non-polar molecules

ex) C-C, C-H, CH₄

Question 16

dipole-dipole

Answer 16

occurs in all polar molecules

ex) C-O, C-N, C-S, P-O

Question 17

hydrogen bonding

Answer 17

specialized dipole-dipole interaction:

X-H - - - - :Y
X/Y: N, O, (F)

H-bond donors: gives H away
H-bond acceptor: attracts the H

Question 18

ion-dipole

Answer 18

strong interaction between a full formal charge and a dipole

ex) H₂O-[Nitrogenous drug]⁺

Question 19

electrostatic interactions (ion-ion)

Answer 19

ionic interactions between a cationic portion and anionic portion

two NMs w/ formal charges

(+) & (-)
effective at distances farther than other types of interactions

ex) O₂^--N⁺

Question 20

covalent bonds (this is an inTRAmolecular force)

Answer 20

strongest interactions
limited reversibility
seldom formed