17 - Non-Covalent Bonds

Question 1

Main Non-covalent interactions

Answer 1

electrostatic:
- ionic
- dipole-dipole
- dipole ion interactions

Hydrogen bonds
London Forces (Van der Waals)
Hydrophobic/hydrophilic

Question 2

why weak bonds important in biology
- examples

Answer 2

• non-covalent interactions are:
• individually weak
• collectively strong

e.g.
- membrane must be semi-fluid
- proteins must be flexible
- DNA strands must come apart (weak hydrogen bonds)
- fibre must be strong and rigid, but flexible
- storage molecules must be easily accessible for enzymes - e.g. glycogen

Question 3

polar covalent bonds info

Answer 3

• oxygen holds onto electrons tighter than hydrogen
• electronegativity is the ability of an atom to attract electrons to itself
• electronegativity increases from bottom left of periodic table to top right

Question 4

Hydrogen bonds info

Answer 4

• a dipole-dipole interaction
• polar covalent bond between hydrogen (electron donor) and oxygen and nitrogen (electron acceptors, as they have lone pairs)
• strength of hydrogen bonds depends on the angle of the bond
• hydrogen bonds found in DNA in nitrogenous bases and between complementary bases

Question 5

Ionic bonds

Answer 5

ions can lose or donate electrons in to other ions to become more stable as a molecule
- e.g. NaCl

Question 6

Ionic bonds and salt bridges

Question 7

London Forces/Van Der Waal’s bonds

Answer 7

• weak electrostatic interaction
• induced dipole interactions
• interaction between atoms close in space
• important in macromolecular structures
  e.g. atoms tightly packed in proteins, membranes, etc.

Question 8

properties of water
- applications in biology and real world

Answer 8

• good solvent
• cause of hydrophobic interactions: bio-membranes, proteins
• high specific heat capacity: good heat transport - blood circulation
• high latent heat of vaporisation - good cooling agent - sweating mechanism
• freezes from top downwards - survival in seas and lage water bodies
• strong cohesion and adhesion - hydrogen bonding
• useful for pond skater, contact lenses
• important for capillary action and compressibility

Question 9

hydrogen bond formation in water

Question 10

water structure when frozen - ice