Section A: Non-Covalent Interactions

Question 1

Differences between covalent and non-covalent interactions

Answer 1

1. Covalent have a shorter range
2. Covalent are more highly directional
3. Covalent more long-lasting

Question 2

If more than 1 bond in a molecule is polar then

Answer 2

The overall molecular dipole, u, must be considered

Question 3

The overall average interaction energy between freely rotating dipolar molecules is dependant on

Answer 3

The distance between them : E ~ - 1/r^6

and inversely dependant on temperature

Question 4

How are non-polar molecules held together?

Answer 4

The electrons in a molecule can be polarised due to the influence of a polar molecule. The permanent dipole and induced dipole can then attract.

Question 5

Dispersion Interaction

Answer 5

Fluctuating electron density can cause a instantaneous dipole in non-polar molecules that induce a dipole in neighbouring molecule. These induced dipoles attract

Question 6

Polarisability

Answer 6

The size of a permanent dipole

Question 7

Dielectric constant

Answer 7

Measured experimental values that determine how well a material stores electrical energy when exposed to an electric field -> property of the bulk substance

Question 8

Generally more polar molecules have

Answer 8

Higher dielectric constants

Question 9

When an ion is surrounded by polar molecules,

Answer 9

Many of their dipoles align in the field of the ion which lowers self-energy of ion

Question 10

Why are H-bonds generally short ranged?

Answer 10

The formation of H bonds involves overlap of AO’s

Question 11

Why are the properties of water anomalous?

Answer 11

Each water molecule can form up to 4 H-bonds with other water molecules, 2 as acceptors 2 as donors

Question 12

The Grotthuss Mechanism

Answer 12

Conduction of H+ through water is an order of magnitude faster than conduction of similarly charged ions. This is because H bonds can become covalent bonds (visa versa) allowing transfer of charge from one location to another without diffusion of atoms.

Question 13

In TLC, the mobile phase is driven by

Answer 13

Capillary forces

Question 14

In TLC, affinity to stationary phase is dependent on

Answer 14

Strength of non-covalent interactions

Question 15

Why do systems with H-bonds have high entropy?

Answer 15

There are many ways of arranging the H bonding network, each of the same energy

Question 16

Hydrophobic molecules

Answer 16

Can’t form H-bonds -> reduces entropy

Question 17

The hydrophobic effect

Answer 17

Clustering of non-polar molecules due to entropically unfavourable interaction with water

Question 18

Amphiphile

Answer 18

Both hydrophobic and hydrophilic e.g. lipids

Question 19

Amphiphile self-assembly

Answer 19

Amphiphile’s self assemble in order to minimise the hydrophobic effect