Water

1
Water

• Most important and abundant biological molecule
• Chemical formula H2O
• 2 Hydrogen molecules covalently bonded to 1
  Oxygen Molecule
• Obtains most of it's properties due to it's
  Polarity and shape.
• Electrons are shared unequally
• Oxygen has a high electronegativity, so it
  "possesses" the electrons more than hydrogen.
• Hydrogen Atoms are spaced 104.5O apart.
• Results with the water atom having a () charged
  H side and a (-) charged O side.

2
Hydrogen Bonding

• High polarity results in H2O's ability to form
  Hydrogen Bonds.
• Hydrogen bonds are formed by the attraction of
  the charged portions of the H2O molecule to the
  charged portion of other H2O molecules, Ions, or
  other polar molecules.

3
Cohesion

• This allows for high cohesion properties of water
  (ability to attract to itself). Allows water to
  have high specific heat, and heat of vaporization
  because of the strong attraction of H2O
  molecules.
• This also explains why water actually expands as
  it freezes

(Note There is something SERIOUSLY wrong with
this diagram. What is it?)
4
Adhesion

• Adhesive properties make H2O a powerful solvent.
• Polar portions of H2O molecule can "pluck off"
  Ions from an Ionic crystal lattice.

5
Interactions with Non-polar Molecules

• Water Organizes nonpolar molecules.
• Nonpolar molecules are hydrophobic (repelled by
  H2O)
• Repulsion forces these molecules into particular
  arrangements.
• Example is the lipid bilayer found in cellular
  membranes.

6
Water and pH

• Water disassociates (ionizes) in itself.
• Basis for the pH scale of acid - base
  measurement.
• Water can disassociate from H2O to H (Hydrogen
  Ion, acid) and OH- (Hydroxide Ion, base).
• Usually does this for 1/10,000,000 or 1E-7.
• pH is a measure of this dissociation. According
  to the following formula pH -Log H
• Lower pH indicates high H concentration - high
  acidity.
• Higher pH indicates low H concentration (high
  OH- concentration) - High alkalinity.
• A neutral solution has pH7.