Cat’s Cradle
IMPORTANCE OF WATER
• 1,360,000,000 cubic kilometers of water in
the hydrosphere
• 70% of Earth’s surface
• Comprises 60-90% of all living organisms
• Key reactant in both synthetic and
catabolic (i.e. breakdown) reactions
WHY WATER?
The unique physical and chemical properties
of water derive from its molecular structure
POLAR COVALENT BOND
• Oxygen shares eunevenly with
hydrogen due to its
higher
electronegativity
• As a result, the
oxygen end of the
molecule appears
negatively charged
while the hydrogen
end appears positive
WHY IS THE POLAR COVALENT
BOND SO IMPORTANT?
WATER EXHIBITS BOTH ADHESIVE &
COHESIVE PROPERTIES DUE TO POLAR
COVALENT BONDING
ADHESION
• Water molecules stick
to other charged
particles
• Because water is
adhesive it also has
the properties of
– Universal solvent
– Capillary action
UNIVERSAL SOLVENT
• “Like dissolves like”
• Water dissolves polar
solutes.
• Water cannot easily
dissolve non-polar
solutes (i.e. fats, oils)
Why is the ability of water to serve as a nearly
universal solvent biologically important?
CAPILLARY ACTION
• Water adheres to
sides of tubes and
other charged
surfaces, rising
against force of
gravity
Why is capillary action a
biologically significant property?
COHESION
• Water molecules stick
to themselves
• Because water is
cohesive it exhibits
the properties of
– High Heat of
Vaporization
– High Surface Tension
HEAT OF VAPORIZATION
• Because water
molecules cohere,
more energy is
required to break
them apart
(i.e. evaporation)
• Non-polar substances
have less cohesion
and hence lower
heats of vaporization
VAPORIZATION OF WATER ON
A MOLECULAR LEVEL
Why is heat of vaporization
biologically significant?
STABILITY OF
AQUATIC
ECOSYSTEMS
Prevent Changes In Solubility of
Gases In Blood Plasma
Apocrine & Eccrine Glands
Surface Tension
• As water interfaces
with air at the surface,
water molecules
cohere, creating a
less penetrable
surface
• Surfactants are
substances that break
surface tension
Why is surface tension a
biologically significant property?
RDS – Respiratory Distress Syndrome
Properties of Water
Review of Concepts
What type of bonding is exhibited between oxygen and
hydrogen in water molecules?
A
Van der Waal
B
Polar Covalent
C
Ionic
D
Intermolecular
Which property best explains why the bond is polar?
A
Mass
B
Density
C
Shape
D
Electronegativity
True or False? The tendency of water molecules to stick together is an
adhesive property
A
True
B
False
Which property of water explains why aquatic ecosystems tend
to be more stable in terms of temperature than terrestrial
ecosystems?
A
Heat of Vaporization
B
Conductivity
C
Surface Tension
D
Capillary Action
True or False? Capillary action is a
property of water that is attributed
to the adhesive nature of water.
A
True
B
False
The ability of some insects to live on the
surface of pond (due to the naturally high
surface tension of water) can be
negatively impacted by which
substances? Type your answer!
Due to its polar nature, water has the unique
ability to break apart other polar
substances. This property of water is
called...
A
Heat of Vaporization
B
Capillary Action
C
Ability to exist in three states
D
Universal Solvency
Carbon Dioxide, like water, contains
covalent bonds, yet CO2 does not
exhibit any of the properties of
water. This is because while the
bonds of CO2 are covalent they are
not _______.
Because these properties of water do not
depend upon the amount of matter (unlike
mass or pH), these properties are....
A
Extensive
B
Intensive