Water has many unique properties due to its polar molecular structure and ability to form hydrogen bonds. These properties include high surface tension, adhesion, capillarity, high heat capacity, high heat of vaporization, and being less dense as a solid than in liquid form. Water's hydrogen bonding enables it to act as a solvent, dissolving many other polar substances and allowing important biochemical processes to occur.

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< 0o
C - ice; 0o
C - 100o
C – liquid; > 100o
C - steam

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Water’s Properties
• Cohesion
• Adhesion
• Capillarity
• High Specific Heat
• High Heat of Vaporization
• Solid water (ice) is less dense than liquid
• Solvent
• Transparent

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Cohesion
• Water clings to polar
molecules through
hydrogen bonding
– Cohesion refers to
attraction to other
water molecules.

responsible for
surface tension

a measure of the
force necessary to
stretch or break
the surface of a
liquid

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– Adhesion refers
to attraction to
other
substances.

Water is
adhesive to
any substance
with which it
can form
hydrogen
bonds.
Adhesion

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Capillary action
water evaporates from
leaves = transpiration
adhesion,
cohesion and
capillary action
All thanks
to hydrogen
bonding!
water taken up by
roots

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•trees have specialized structures to transport water:
xylem and phloem “plumbing”
• water molecules are “dragged” from the roots to the
top of the tree by capillary action and cohesion:
hydrogen bonds help water molecules to each other

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“Universal” Solvent
• A liquid that is a completely homogeneous
mixture of two or more substances is called a
solution.
– A sugar cube in a glass of water will eventually
dissolve to form a uniform mixture of sugar
and water.
• The dissolving agent is the solvent and the
substance that is dissolved is the solute.
– In our example, water is the solvent and sugar
the solute.
• In an aqueous solution, water is the solvent.
• Water is not really a universal solvent, but it is
very versatile because of the polarity of water
molecules.

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• Water is an effective
solvent as it can form
hydrogen bonds.
– Water clings to
polar molecules
causing them to be
soluble in water.

Hydrophilic -
attracted to
water
– Water tends to
exclude nonpolar
molecules.

Hydrophobic -
repelled by water

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• Water transports molecules dissolved in it
– Blood, a water-based solution, transports
molecules of nutrients and wastes
organisms
– Nutrients dissolved in water get
transported through plants
– Unicellular organisms that live in water
absorb needed dissolved substances

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Solid water (ice) is less dense than liquid
same mass
but a larger
volume
• Ice is less dense than water: the molecules are
spread out to their maximum distance
Density = mass/volume

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
water expands as it
solidifies

water reaches
maximum density at
4-degrees C

water freezes from the
top down

organisms can still
live in the water
underneath the ice
during winter
Oceans and lakes don’t freeze solid
because ice floats

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Water is Transparent
• The fact that water is clear allows light to
pass through it
– Aquatic plants can receive sunlight
– Light can pass through the eyeball to
receptor cells in the back