6. Hydrogen Bonds and Water

Question 1

State 4 unusual properties of water

Answer 1

• High melting point
• High boiling point
• High surface tension
• Expands upon freezing

Question 2

Highly __________ atoms have a higher affinity for electrons so tend to pull them towards themselves.

Answer 2

Electronegative

Question 3

Give 4 examples of highly electronegative atoms

Answer 3

• Oxygen, O
• Nitrogen, N
• Fluorine, F
• Chlorine, Cl

Question 4

Why do electronegative atoms interact with hydrogen?

Answer 4

The bonds in each molecule have a high polarity (even if the overall molecule is non-polar).

Question 5

What is a hydrogen bond?

Answer 5

A dipolar interaction between bonds involving hydrogen.

Question 6

What type of dipole is a hydrogen bond?

Answer 6

Permanent

Question 7

What is the typical strength (kT) of Van der Waals/dispersion forces?

Answer 7

2 kT

Question 8

What is the typical strength (eV) of Van der Waals/dispersion forces?

Answer 8

0.004 - 0.04 eV

Question 9

What is the typical strength (kT) of hydrogen bonds?

Answer 9

4 - 16 kT

Question 10

What is the typical strength (eV) of hydrogen bonds?

Answer 10

0.1 - 0.4 eV

Question 11

What is the typical strength (kT) of covalent bonds?

Answer 11

100 kT

Question 12

What is the typical strength (eV) of covalent bonds?

Answer 12

2 - 8 eV

Question 13

What structure do water molecules pack into?

Answer 13

An open tetrahedral structure

Question 14

Why do water molecules pack into an open tetrahedral structure?

Answer 14

Because hydrogen bonds have a directional nature.

Question 15

Is water more dense as a solid or liquid?

Answer 15

Liquid

Question 16

A hydrogen bond is a ______-______ interaction between specific ________ ______.

Answer 16

Dipole-dipole
Functional groups

Question 17

Molecules which form many H-bonds with neighbours have _____ dissociation energies so they are ____ sticky.

Answer 17

Higher
More

Question 18

How is hydrogen bonding used in nanoscience?

Answer 18

Molecules can be designed based on the directionality of H-bonds to form supramolecular aggregates that form via molecular self-assembly.

Question 19

Give 3 examples of where hydrogen bonds are found in nature

Answer 19

• Protein: alpha-helix
• Protein: beta-sheet
• DNA: base pair bonding

Question 20

Are hydrogen bonds attractive or repulsive?

Answer 20

Attractive