Water has unique properties that support life due to its molecular structure and ability to form hydrogen bonds. The polar nature of the water molecule, with slightly positive and negative ends, allows it to form hydrogen bonds with other water molecules. This gives water high surface tension, adhesion, cohesion, heat capacity, and the ability to dissolve many substances. It also explains why ice floats on liquid water, maintaining the viability of aquatic ecosystems.

1. Water’s Life-Supporting
Properties

2. The structure of Water
The end with
the two
hydrogen atoms
is slightly
positive.
Oxygen end of the molecule has a slight
negative charge
POLAR MOLECULE!!

3. The electromagnetic
attractive interaction
between polar
molecules, in which
hydrogen (H) is
bound to a highly
electronegative
atom, such as
nitrogen (N), oxygen
(O) or fluorine (F).
Hydrogen bond
is not a true bond but a strong dipole-
dipole attraction, and should not be
confused with a covalent bond

4. Q:How can water molecules
be compared to magnets?
A:Both water molecules and magnets have opposite poles that
cause them to be attracted to each other in a specific
orientation.

5. Life-Supporting Properties of WATER
WATER
H2O
Cohesion
&
Adhesion
Related to
high surface
tension
Temperature
Moderation
(High heat capacity)
Dissolve
Substances
(Universal solvent)
Low
density of
ice
(changes in
density)
The polar nature of
water and the
effects of hydrogen
bonding explain
most of water´s
unique properties

6. Life-Supporting Properties of WATER Cohesion &
Adhesion
Related to
high surface
tension
COHESION: property of like molecules (of
the same substance) to stick to each other
due to mutual attraction with HB.
ADHESION: property of different molecules
or surfaces to cling to each other thanks to
HB
Surface tension:Molecules are
pulled equally in all directions by
neighboring molecules
Capillary Action:
When a liquid flows
through a narrow space

7. Life-Supporting Properties of WATER
COHESION
+
ADHESION
Surface tension: Result of cohesive
forces between adjacent molecules
Molecules are pulled equally…
Capillary Action: the result of
cohesive and adhesive forces…
When a liquid flows through a
narrow space

9. Life-Supporting Properties of WATER Temperature
Moderation
(High heat
capacity)
TEMPERATURE measure of the average
energy of random motion of the particles in a
substance.
When two substances differ in
temperature, thermal energy in the
form of heat is transferred from the
warmer substance to the cooler
one
water heats up much more slowly than
metal→ because of hydrogen bonding, water
has a better ability to resist temperature
change than most other substances
THERMAL ENERGY total amount of
energy associated with the random movement
of atoms and molecules in a sample of matter

10. Life-Supporting Properties of WATER
Temperature
Moderation
(High heat
capacity)
THERMAL ENERGY total amount of
energy associated with the random
movement of atoms and molecules in a
sample of matter
TEMPERATURE measure of the average
energy of random motion of the particles in a
substance.
.
HB RELATION:
Some thermal energy breaks hydrogen
bonds → water absorbs the same
amount of thermal energy but undergoes
less temperature change than the metal
As water cools, it forms hydrogen bonds
→ releases thermal energy in the form of
heat, so there is less of a drop in
temperature than in metal

11. Life-Supporting Properties of WATER
Dissolve
Substances
(Universal
solvent)
SOLUTION Uniform mixture of two or
more substances
SOLVENT The substance that dissolves the
other substance and is present in the greater
amount
SOLUTE The substance that is dissolved
and is present in a lesser amount
HB RELATION: areas of slight electric charge
attract the polar ends of water molecules.
Water molecules cling to these charged
regions and separate the sugar molecules
from one another
EXAMPLE
Sodium chloride dissolves as Na+ and
Cl-ions become attracted to water
molecules and break away from the
surface of the solid

12. Life-Supporting Properties of WATER
Low density
of ice
(changes in
density)DENSITY: amount of matter
in a given volume.
In most substances the solid state is
more dense than the liquid. Water is
just the opposite—its solid form (ice) is
less dense than the cold liquid form
Ice floats because its molecules
are less densely packed than
those in liquid water.
HB RELATION: Because the molecules in liquid
water are moving faster than those in
ice, there are fewer and more short-lived
hydrogen bonds between molecules. The
liquid water molecules can fit more closely

13. Video water’s life-supporting
properties
• http://www.youtube.com/watch?v=aVmU3CL
xvgU 4 MIN
• http://www.youtube.com/watch?v=HVT3Y3_g
HGg 11 MIN