Water  Most important and abundant biological molecule

 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.
Hydrogen Bonding
 High polarity results in H2O's ability to form Hydrogen
 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
 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
 This also explains why water actually expands as it freezes
(Note: There is something SERIOUSLY wrong with this diagram. What is it?)
 Adhesive properties make H2O a powerful solvent.
 Polar portions of H2O molecule can "pluck off" Ions
from an Ionic crystal lattice.
Interactions with Non-polar Molecules
 Water Organizes nonpolar molecules.
 Nonpolar molecules are hydrophobic (repelled
by H2O)
 Repulsion forces these molecules into particular
 Example is the lipid bilayer found in cellular
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 OHconcentration) - High alkalinity.
 A neutral solution has pH=7.