Transcript water molecules are - Solon City Schools

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Polar Covalent vs. Nonpolar Covalent
• Polar covalent- which means 2 different
nonmetals (ex. water or ammonia) (have
opposite charges on molecule b/c
electrons are slightly more attracted to
oxygen)
– Unequal sharing of electrons
• Nonpolar Covalent- means 2 of the same
nonmetals (ex. Oxygen or nitrogen gas)
and they do not have opposite charges
and share electrons equally.
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< 0o C - ice;
0o C - 100o C – liquid; > 100o C - steam
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• Water consists of an
Water is a Polar Molecule
oxygen atom bound to
-has oppositely charged
two hydrogen atoms by
ends
two single polar
covalent bonds.
– Oxygen has unpaired
& paired electrons
which gives it a
slightly negative
charge while
Hydrogen has no
unpaired electrons
and shares all others
with Oxygen
– Leaves molecule with
positively and
negative charged
ends
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Water molecules form Hydrogen
bonds
slightly positive
charge
hydrogen bond
between (+) and (-)
areas of different
water molecules
slightly negative
charge
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Water’s Properties
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Surface Tension
Cohesion
Adhesion
Hydrophilic
Hydrophobic
Solid water (ice) is less dense than
liquid
• Solvent
• Transparent
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How water molecules cling Cohesion
together by hydrogen bonding
-water molecules stick together
to climb up a stem
– 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
– Hydrogen bonding allows
water to behave like its
coated w/ an invisible film
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– Adhesion –how water
molecules can stick to
different things;
– Water molecules stick
to a plant’s stem &
climb up a plant to
reach the leaves to do
photosynthesis
– refers to attraction to
other substances.
Adhesion
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Capillary action
water evaporates from
leaves = transpiration
adhesion,
cohesion and
capillary action
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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Water is an effective solvent as it
can form hydrogen bonds.
– Water clings to polar
molecules causing them to be
soluble in water.
– “Like dissolves Like”
• Hydrophilic - attracted to
water (likes water); usually
ionic or polar substances
(ex. Salt)
• Hydrophobic - repelled by
water
• Usually non-polar/non-ionic
substances
•
ex. oil
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Solid water (ice) is less dense
than liquid
• Ice is less dense than water: the molecules are
spread out to their maximum distance
Density = mass/volume
same mass
but a larger
volume
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Oceans and lakes don’t freeze
solid because ice floats
 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
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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.
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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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Water is Transparent
• The fact that water is clear allows light
to pass through it
– Aquatic plants can receive sunlight
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