WATER
Describe water molecules.
Tell what causes polarity in water
molecules, and tell at least 5
effects of the polarity of water.
(You will turn in notes that show this information.)
Name
Table ____ Period ____
Water Notes
Polarity of water is caused by:
Effects of water’s polarity:
1.
2.
3.
4.
5.
Water is an important
and abundant biological
molecule.
Our bodies are about 70%
water, and plants can be
up to 90% water.
We need more water than
any other nutrient-- we
could only survive a few days
without it.
Water is smallest and most
simple food molecule: just 3
atoms, but the way those
atoms combine gives water
special properties.
When an oxygen atom
combines with 2 hydrogen
atoms, they stabilize into an
H2O molecule,
by sharing
electrons in
covalent bonds.
However, the way the electrons are shared
gives:
the oxygen end a slightly negative charge,
and the hydrogen end a slightly positive
charge.
It is a
polar
molecule.
The polar charges
of the molecules
attract water
molecules to each
other.
These attractions
are called
hydrogen bonds.
1.What makes a water
molecule “polar”?
2.What are hydrogen bonds
in water?
Although the
hydrogen bonds are
not strong, there
are so many of
them in water that
they have a
significant effect.
The polarity/hydrogen bonds of
water cause important effects.
Effects of water’s polarity
Water
molecules stick
to each other
and to other
polar
substances.
COHESION
Sticking together.
Cohesion is the force
between particles of a
substance that makes
them stick together.
From Latin
co=together
haerēre =to stick
ADHESION
• Sticking to.
Adhesion is the
force that makes 2
unlike bodies stick
together.
From Latin
ad = to, towards, near
haerēre =to stick
Because of cohesion and adhesion:
Water-based
liquids will overfill a cup. You will
need to use a
liquid measuring
cup to get an
accurate reading.
Because of cohesion and adhesion:
Water-based liquids will stick to the edge of a
cup and form a
meniscus.
When you see 2 lines at the top of your liquid,
the bottom one is the measuring level,
the top one is the meniscus.
Because of cohesion and adhesion:
Plants pull water with
nutrients in.
People and animals
transport oxygen and
nutrients in blood
through their
capillaries.
BECAUSE WATER IS POLAR
Polar
substances
dissolve in it.
This let’s water:
• combine with carbohydrates to swell
and break down starch molecules
• help form gluten strands that give
breads their structure
• carry minerals and water-soluble
vitamins.
• attach to proteins and carbohydrates
in dough, then turn to steam during
baking, causing doughs to rise and
keeping crusts moister.
• dissolve reactants so chemical
reactions can begin.
BECAUSE WATER IS POLAR:
The hydrogen
bonds in water
hold the
molecules
together,
so water has a
higher boiling and
freezing point
than many other
substances.
It is available
as a liquid in
the climates
inhabited
by humans.
It boils at
temperatures
hot enough
to cook foods.
BECAUSE WATER IS POLAR:
As water freezes, the
hydrogen bonds cause
the molecules to
arrange themselves into
a crystal structure that
actually spreads them
farther apart. This
makes the ice take up
more space than the
water did. Because it is
less dense than the
liquid water, ice floats.
THIS IS IMPORTANT!
Floating ice helps insulate the water below it, protecting
fish and other life from the cold. If ice sunk,
new water would be exposed to the cold at the top.
Then THAT water would freeze and sink,
then new water would exposed to freeze and sink, then …..
But when freezing water expands, it
can also cause problems:
One problem is that ice crystals can
puncture cell walls:
When the food thaws,
fluid leaks out of the
ruptured cell wall, and
the food can become
mushy.
Damage from freezing and thawing is
More likely in foods
with lots of moisture
than in foods
with little moisture.
Discuss 5 effects
of water’s
polarity.
Did you reach
our learning targets?
1.Describe water molecules.
2.Tell what causes polarity in
water molecules
3.Tell at least 5 effects caused
by the polarity of water.
(See next slide to re-check note set-up.)
Turn in your notes.
Be sure you have included: