Water and Life
How the properties of water enable life to exist
Cohesion occurs when water molecules stick to
each other.
Adhesion is when water molecules stick to other
surfaces.
Adhesion allows water to stick to the veins of plants,
and Cohesion allows the water to stay together as it
travels through the veins.
Surface
Tension- Elastic
like force
existing on the
surface of a
liquid, usually
minimizes the
surface area
Insects can walk on the surface
tension of water. Is this an example
of cohesion or adhesion?
Cohesion!
Why?
 Water molecules cohere or stick
together, forming a kind of skin called
surface tension. This “skin” allows for
insects to sit on top of water.
Ice floats allowing organisms to survive in
winter.
This is because Ice is less dense than water
and water molecules cohere to each other
Large bodies of water change temperature
slower than land:
Coastal temperatures are cooler in the summer and
warmer in the winter than inland areas.
Water can form solutions
and dissolve salts and
sugars.
Solute- what is being dissolved
Solvent- What is doing the dissolving
ExampleSugar = solute
Water = Solvent
*Water is the universal solvent*
Water is a polar
molecule
How water molecules form polar covalent bonds
When water forms
a covalent bond,
Oxygen does not
share all of its
electrons with
Hydrogen.
Oxygen has two
pairs of electrons
that are not shared
with the hydrogens
Molecules that do not share its electrons evenly
are called polar molecules. One end of a polar
molecule is slightly negative while the other end
is slightly positive.
Polar molecules are like magnets:
When two or more polar molecules come into
contact, they form a weak attraction called a
Hydrogen bond.
*remember
that opposite
charges
attract!
Hydrogen bonds
make water molecules sticky
Notice how the
opposite charges of
each water molecule
are facing each other--
Hydrogen bonds can form between
any two polar molecules.
Solid water is less dense than liquid
(so it floats!)
 Hydrogen
bonds are
attracted to
each other but
are still able
to move freely
 The cold temperatures freeze
the hydrogen bonds in place
When the solute
dissolves in the
solvent, it forms a
solution.
The charged ends
of water are
attracted to the
charged ions that
make up salt.
www.mhhe.com/physsci/chemistry/essenti
alchemistry/flash/molvie1.swf
In liquids, water can dissociate to form
hydroxide (OH-) and hydrogen (H+) ions.
Solubility- the ability for a
solute to dissolve in a solvent
Insolublewhen a
substance is
unable to
dissolve in a
solvent.
Summary
1. Water is a polar molecule because the
oxygen end is slightly negative and the
hydrogen end is slightly positive
2. Polar Molecules can form hydrogen
bonds
3. Hydrogen bonds make water molecules
sticky—causing cohesion and adhesion
4. These qualities allow life to exist
1.The properties of water are extremely
important to trees!!
Identify and explain each property of
water a tree relies on.
1. Polarity – forms hydrogen bonds, and
allows water to be easily transported
from the soil to the roots. Waters polarity
also allows water and mineral nutrients
to travel from the roots to the different
parts of the plant.
2. Cohesion/Adhesion - the large
negative side of the oxygen promotes
hydrogen bonding as it attracts the
positive hydrogen sides of the other
water molecules. This allows water to
adhere to the veins and roots and allow
the water to travel throughout the plant
2.Like dissolves like: So, polar molecules will
dissolve in other polar molecules.
Explain why nonpolar molecules, like lipids,
not dissolve in water.
Non polar molecules do not contain charged
ends, therefore the water molecule is not
attracted to it and will not break up the nonpolar molecule to dissolve it (think of the salt
water animation)