Properties of
Water
What molecule supports all
of life?
Water Cycle
What is a polar molecule?
• Has polar bonds:
• Water has polar covalent bonds
• Oxygen is more electronegative than H
• Electrons of covalent bonds spend
more time closer to Oxygen than to H
• Creates a polar molecule
• O region is partially negative
• H regions are partially positive
• Causes the properties of water
POLAR MOLECULE
–
O
H
+
H
H2O
+
–
HYDROGEN BONDS
+
Water
(H2O)
+
Hydrogen bond
–
Ammonia
(NH3)
+
+
+
States of Water
How does this change when
water is in different states?
• Slightly positive H of 1 molecule is attracted to
slightly negative O of nearby molecule creating a
H bond that holds those molecules together
Water and Polarity
Hydrogen
bonds
What are the Properties of
Water?
•
•
•
•
•
•
Adhesion
Cohesion
Surface Tension
High specific heat
Expands when frozen
Universal solvent
1. Cohesion
• Cohesion – water “sticking” to itself
1. Cohesion
• Cohesion contributes to transport of
water and dissolved nutrients against
gravity in plants
2. Adhesion
Adhesion is water
“sticking” to
something else
• Cohesion is supported by Adhesion
• What is Adhesion?
• clinging of one substance to another
• Adhesion of water to cell walls by
those same hydrogen bonds
Adhesion vs. Cohesion
3. Surface Tension
• How is this related to Surface Tension?
• Surface tension= how difficult it is to
stretch or break the surface of a liquid
Examples of surface
tension
Benefits of properties 1-3:
• Bugs that walk on water
• Bugs that use air bubble to breathe underwater
• Leads to transport of water and its dissolved
nutrients against gravity in plants
• Water molecules leaving plants by evaporation
cause H bonds to tug on water molecules,
creating an upward force of water in the plant
Water and Temperature
Hydrogen
bonds
4. High Heat Capacity
a.k.a. High Specific Heat
•Water’s temperature does not change
easily
•Water can absorb or release a good
deal of heat before its overall
temperature changes.
What is specific heat?
• the amount of heat that must be absorbed or
lost for 1 g of that substance to change its
temperature by 1 °C
Evaporative Cooling
Benefits of having a
high heat capacity:
• Keeps temperatures more constant in bodies of water so
animals can survive better
• Keeps water warm on a cool day and cool on a hot day, and
in turn, cools the air around it on a hot day and heats air
around it on a cool day
• Keeps temperature from fluctuating greatly due to the fact
that oceans cover the earth
• Helps moderate Earth’s climate
• Contributes to stability of temperature in lakes and ponds
• Prevents land organisms for overheating
What happens to the ice?
5. Expansion Upon Freezing
• Water is less dense as a solid than as a liquid
• Ice Floats
• Begins freezing when its molecules are no
longer moving vigorously enough to break
their hydrogen bonds
• Becomes about 10% less dense
Hydrogen Bond angles
Benefits of water
expanding upon freezing:
•Fish get to survive in cold
temperatures
•We get cold drinks
6. Universal Solvent
A few terms regarding
solutions…
• Solution• Liquid that is completely homogeneous mixture of
two or more substances
• Solvent• Dissolving agent of a solution
• Solute• Substance that is dissolved
• Aqueous solution• Solution in which water is the solvent
Solution
Suspension
Colloid
(This is why you should shake milk first!)
Why is water a versatile solvent?
• Due to polarity of the ions
• Ions have mutual affinity through electrical attraction of
the opposite charges
• Compounds don’t have to be ionic to dissolve water
• Dissolve when water molecules surround each of the solute
molecules, forming hydrogen bonds with them
•Hydrophilic – any substance that
“loves” water and dissolves easily
into it
•Hydrophobic – any substance that
“hates” or repels water and will not
mix with it
Benefits of water’s solubility:
•Allows the movement of solvents
through cohesion
•Makes the solvent hydrophilic,
benefitting cellular processes
QUIZ TIME!
• The model illustrates hydrogen bonding found in water. This attraction
between water molecules is the result of water’s
• A ionic bonding.
• B polar covalent bonding.
• C positively charged atoms.
• D negatively charged atoms.
Which property of water
is displayed here?
Which property of water
is displayed here?
Which property of water
is displayed here?
Which property of water
is displayed here?
Which property of water
is displayed here?
Which property of water
is displayed here?