11A - Intermolecular Forces

Question 1

Def: What is a phase? What are the 3 (or 5 if you’re smart) kinds.

Answer 1

Physically distinct, homogeneous part of a system comprised of one physical state of matter:
1. BE Condensates
2. Solids
3. Liquids
4. Gases
5. Plasmas

Question 2

Def: What are the two types of energies that the states are dependent on the balance between?

Answer 2

EP: Potential energy or stored energy, which in the form of attractive forces draws particles together
KE: Kinetic energy, the energy of motion which tends to disperse particles

Question 3

Def: What is temperature, and what is it in relation to Avogadro’s number, R, and average energy per mol.

Answer 3

Average KE of group of particles.
T = (2/3) (Na/R) (0.5mu^2)
R = 8.3145 J/mol*K

Question 4

Def: What two things are thermodynamics of phases dependent on the balance between?

Answer 4

Enthalpy: Transition btw phases and interruption of IMFs due to q changing, but T remaining constant at phase change
Entropy: Increasing disorder in a system through increasing phase changes

Question 5

Theory: Describe the shapes, volumes, compressibility’s, and flows of solids, liquids, and gases.

Answer 5

Solids: Fixed shape, fixed volume, incompressible, no flow
Liquids: Variable shape, fixed volume, low compressibility, moderate flow
Gases: Variable shape, variable volumes, highly compressible, high flow

Question 6

Theory: Explain why, in relation to KE, some phases have higher ability to fill up a container.

Answer 6

High KE = high movement = easier to escape neighboring molecules = filling up container more.

Question 7

Def: What is a phase change?

Answer 7

Phase changes involve the forming, breaking or changing the strength of intermolecular forces.

Question 8

Theory: Explain the effects of KE and IMFs on the phase of a substance.

Answer 8

KE: Keeps particles moving, apart.
IMFs: Attraction, keeps particles together.

Question 9

Def: What is an IEMF? How do they compare to bonding forces

Answer 9

Intermolecular forces.
Attractive, electrostatic forces that exist between all molecules, ions and atoms.
Relatively weaker.

Question 10

Def: What are the 3 types of bonding, known as IMFA’s?

Answer 10

1. Ionic: Cation-Anion
2. Covalent: Sharing of e- pairs.
3. Metallic: A cation in a delocalized see of e-.

Question 11

Def: What are the 7 types of IMFE’s?

Answer 11

1. Ion-Dipole: Ionic charge and dipole charge
2. H-Bonds: A polar bond to H and a dipole charge
3. Dipole-Dipole (Stationary solids/liquids): Dipole charges
4. Ion-induced dipole: Ionic charge to polarizable e- clouds.
5. Dipole-Dipole (Rotating gas): Dipole charges
6. Dipole-induced dipole: Dipole charge to polarizable e- clouds.
7. LDF’s: btw polarizable e- clouds.

Question 12

Theory: How do IMFE’s explain bp, mp, vp, st, viscosity, and capillary action?

Answer 12

IMFE’s are all electrostatic, meaning btw + and - species.
More IMFE’s means higher bp and mp. Reaching bp or mp means breaking IMFE’s, not IMFA’s. All other properties are affected somewhat by IMFE’s

Question 13

Def: What is r?

Answer 13

Distance across which EP (attractive interactions) interaction are felt.

Question 14

Def: Why is there a limit on how close molecules can be, and what is it? At what distance do interaction rapidly fall of.

Answer 14

There is a limit as at short distances, repulsive forces will dominate. For LDF’s, it’s 1/r^12 At about 1/r^6 , interaction falls of.

Question 15

Def: Define ion-ion interactions. What is their effect, and comment on their directionality. What is the EP equivalent to?

Answer 15

Oppositely charged ions attracting.
1/r
Non-directional.
Crystal lattice energy, where ions form extended repeating units.

Question 16

Def: Define ion-dipole forces. What is their effect, and what is hydration? What major property of ionic compounds does this interaction largely determine.

Answer 16

Attraction between oppositely charged dipole end and ions.
1/r^2
Attraction of water dipole (permanent) to ion.
Solubility.

Question 17

Theory: Explain the effects of cation size and cation charge on hydration of salts.

Answer 17

Smaller cations = stronger ion-dipole = more hydration and vice versa
Higher ionic charge = stronger ion-dipole = more hydration.

Question 18

Def: What is mu (the u letter thing).

Answer 18

A permanent dipole.

Question 19

Def: Define dipole-dipole and dipole moments. What is their effect(s).

Answer 19

Molecules will arrange themselves into lowest energy, least repulsive config. The permanent dipoles adds to the attractive forces btw molecules. These dipole moments cause d-d interactions.
When dipoles are in the same direction, 1/r^3.
When averaged over all possible orientations (rotating gases tend to move), 1/r^6.

Question 20

Theory: How do dipole-dipole affect bp.

Answer 20

Magnitude of dipole moment is one of the main factors affecting bp. Dipole moments increase with polar.

Question 21

Def: Define h-bonds. How do they affect bp and mp. How do they compare to chemical bonds.

Answer 21

Strong IMFE’s, very electronegative atoms to exposed H (not shielded by electron, just a proton). Higher bp and mp. Only about 2-5% as strong as chemical bonds.

Question 22

Def: Define dipole-induce-dipole. What is the effect and why.

Answer 22

Polar mol can interact with non-polar molecules to induce a dipole.
1/r^6, as molecules must be close to induce dipole.

Question 23

Def; What is an induced dipole, and what is its strength based on?

Answer 23

The distortion of a usually symmetrical electron cloud.
Related to polarizability of the molecule and strength of inducing charge of dipole.

Question 24

Def: What is an LDF. What is their effect.

Answer 24

Motion of e- in atoms can cause unequal e- distribution resulting in instantaneous dipoles. These dipoles interact temporarily, having their effect reverse every 10^-16 seconds. Exist in all molecules.
1/r^6

Question 25

Theory: Despite being inert, noble gases can exist as liquids if cold enough. Why?

Answer 25

LDF’s can keep particles together at low temps.

Question 26

Def: What is polarizability? How does it change going through the periodic table and why? What is the relationship btw particle size and polarizability?

Answer 26

Ease with which the e- cloud is distorted.
Increase down a group as atomic size increase, meaning larger e- clouds which distort more easily.
Decrease across a period, as ENC increase.
Smaller particles = electrons held more tightly = less polarizable.

Question 27

Theory: What 3 properties most affect LDF’s.

Answer 27

Increasing size will increase LDF’s.
Increasing polarizability will increase LDF’s.
Increasing area of interaction will increase LDF’s.

Question 28

Theory: What is the general rule, and 3 other rules for comparing IMFE’s.

Answer 28

General: For molecules of same mass and size, IMFE’s increase with polarity.
1. LDF’s always present
2. If similar shapes and #e- btw molecules, difference in magnitude of IMFE’s is dependent on D-D and other kinds (not LDF’s).
3. If molecules differ wildly in #e-, LDF’s are decisive.

Question 29

Theory: What are the 5 rules for assessing LDF’s in molecules.

Answer 29

1. LDF”s always present and become greater in mag w/ increase #e-.
2. Dependent on shape.
3. D-D will add to LDF affects and are found in polar molecules.
4. H-B will do the same a 3, and tend to be stronger than both.
5. None are as strong as bonding forces.