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

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• Water consists of an oxygen atom bound to two hydrogen atoms by two single 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

Water is a Polar Molecule

-has oppositely charged

ends

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slightly positive

charge

slightly negative

charge

hydrogen bond

between (+) and (-)

areas of different

water molecules

Water molecules form Hydrogen

bonds

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Water’s Properties

• Cohesion

• Adhesion

• Capillarity

• High Specific Heat

• High Heat of Vaporization

• Density

• Solvent

• Transparent

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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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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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Capillary actionwater 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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High Specific Heat

– High specific heat

Amount of heat that must be

absorbed or expended to change

the temperature of 1g of a

substance 1o C.

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• A large body of water can absorb a

large amount of heat from the sun in

daytime and during the summer, while

warming only a few degrees.

• At night and during the winter, the

warm water will warm cooler air.

• Therefore, ocean temperatures and

coastal land areas have more stable

temperatures than inland areas.

• The water that dominates the

composition of biological organisms

moderates changes in temperature

better than if composed of a liquid

with a lower specific heat.

Impact of water’s high specific heat ranges from

the level of the whole environment of Earth to that

of individual organisms.

The Earth is over

75% water!

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High Heat of Vaporization

– High heat of vaporization

Amount of energy required to change

1g of liquid water into a gas (586

calories).

large number of hydrogen bonds

broken when heat energy is

applied

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• As a liquid evaporates, the

surface of the liquid that remains

behind cools - Evaporative

cooling.

• Evaporative cooling moderates

temperature in lakes and ponds

and prevents terrestrial

organisms from overheating.

• Evaporation of water from the

leaves of plants or the skin of

animals removes excess heat.

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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.

– 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

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