Learning Goals
1. You will be able to describe
the structure of water.
2. You will be able to identify
the 6 properties of water.
3. You will be able to describe
how these properties are
essential to sustaining life
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Water
3
Types of Bonds: Hydrogen Bonds

Water (H2O or H–O–H) is a polar molecule

Electrons spend more time with O than H’s

H’s become slightly +, O slightly –
4
Hydrogen Bonding




Hold water molecules together
The hydrogen bonds joining water molecules are
weak, about 1/20th as strong as covalent bonds.
They form, break, and reform with great frequency
Extraordinary Properties that are a result of hydrogen
bonds.
 Cohesive behavior
 Resists changes in temperature
 High heat of vaporization
 Expands when it freezes
 Versatile solvent
5
Think-pair-share

Think about the following…




What are the atoms that make up a water
molecule?
Which type of bonds hold the atoms together?
What does polarity mean?
Turn to your shoulder partner and share
your answers
6
Properties of Water
1.
2.
3.
4.
5.
6.
Polar Molecule
Cohesion
High Specific Heat
Density- greatest at 4C
Universal Solvent of Life
Neutral pH
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1. Polarity

Water has a variety of unusual properties
because of attractions between these
polar molecules.
The slightly negative regions of one molecule
are attracted to the slightly positive regions of
nearby molecules, forming a hydrogen bond.
 Each water molecule
can form hydrogen

This leads to
Hydrogen
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2. Cohesion

When water molecules stick to other water
molecules holding them together
Why is this important?
Organisms Depend on Cohesion
Cohesion among water molecules plays a key
role in the transport of water against gravity in
plants
Adhesion, clinging of one substance to another,
contributes
too, as water adheres to the wall of the vessels.
9
Surface Tension

Surface tension, a measure of the force
necessary to stretch or break the surface of
a liquid, is related to cohesion.

Water has a greater surface tension than most
other liquids because hydrogen bonds among
surface water molecules resist stretching or
breaking the surface.
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Surface Tension

Some animals can stand,
walk, or run on water
without breaking the
surface.
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Water as a Transport Medium
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Water evaporates,
pulling the water
column from the
roots to the leaves.
H2O
Water molecules
cling together and
adhere to sides of
vessels in stems.
Water enters a
plant at root cells.
H2O
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3. High Specific Heat

•
•
•
Moderate Temperatures on Earth
Temperature is the measurement of the
movement of molecules
In order for molecules to move faster (get
warmer) the hydrogen bonds holding the
molecules together have to break.
In order for the molecules to move slower
(get cooler) the hydrogen bonds holding the
molecules together have to form.
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Specific Heat

Specific Heat is the amount of heat that
must be absorbed or lost for one gram of
a substance to change its temperature by
1oC.

Water has a High Specific Heat which
means it takes a lot of energy to break or
form the hydrogen bonds between water
molecules
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Specific Heat

Why is this important?
1. Prevention
of temperature changes
that are outside the range suitable for
life.
2. Coastal
3. A
areas having a mild climate
stable marine environment
15
Evaporative Cooling

The cooling of a surface occurs when the liquid
evaporates
 This is responsible for:
 Moderating earth’s climate
 Stabilizes temperature in aquatic
ecosystems
 Preventing organisms from overheating
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Ms. Laslow’s Random Fact
of the Day!!
Most animals cannot sweat like humans
can. They have developed many ways to
cope with the heat.
 Many of which involve evaporative cooling

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Evaporative Cooling of Animals
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Calories of Heat Energy / g
800
Gas
600
540
calories
400
200
Liquid
80
calories
Solid
0
freezing occurs
0
evaporation occurs
20 40 60 80 100 120
Temperature (°C)
a. Calories lost when 1 g of liquid water freezes and
calories required when 1 g of liquid water evaporates.
b. Bodies of organisms cool when their heat is used
to evaporate water.
© Grant Taylor/Getty Images
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4. Density

More dense at 4C
Contracts until 4C
Expands from 4C to 0C
Why is this important?
1. Prevents
water from freezing from the
bottom up.
2. Ice
forms on the surface first—the freezing
of the water releases heat to the water
below creating insulation.
3. Makes
transition between season less
abrupt.
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Density-Ice

Frozen water less dense than liquid water

Otherwise, oceans and deep lakes would fill
with ice from the bottom up

Ice acts as an insulator on top of a frozen
body of water

Melting ice draws heat from the environment
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Density
21
A Pond in Winter
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
ice layer
Protists provide
food for fish.
River otters visit
ice-covered ponds.
Aquatic insects survive
in air pockets.
Freshwater
fish take
oxygen
from water.
Common frogs and pond turtles hibernate.
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5. Universal Solvent

Solutions consist of:





A solvent (the most abundant part) and
A solute (less abundant part) that is dissolved in the solvent
Polar compounds readily dissolve; hydrophilic
Nonpolar compounds dissolve only slightly;
hydrophobic
Ionic compounds dissociate in water


Na+
 Attracted to negative (O) end of H2O
 Each Na+ completely surrounded by H2O
Cl Attracted to positive (H2) end of H2O
 Each Cl- completely surrounded by H2O
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Universal Solvent
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
H
O
O
H
d
-
An ionic salt
dissolves in water.
Na+
H
d
O
H
d-
d- O H
H
d+
d+
H
O H
H
H
d+
Cl–
d+
H
H O
Science 360
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Universal Solvent
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
H O
H
+
d
A polar molecule
dissolves in water.
-
d
+
N
+
d
H
H
d
H
H
O
H
+
d
-
d
-
d
-
d
O
H
H
O
H
H
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6. Neutral pH

pH scale used to indicate acidity and
alkalinity of a solution.

Values range from 0-14
0 to <7 = Acidic
 7 = Neutral
 >7 to 14 = Basic (or alkaline)

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The pH Scale
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
basic
acidic
H+ Ion
Concentration
10 0
10–1
10–2
10–3
10–4
10–5
10–6
10–7
10–8
10–9
10–10
10–11
10–12
10–13
10–14
pH value
0
1
2
3
4
5
6
7
8
9
10
11
12
13
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Examples
hydrochloric acid
stomach acid, lemon
juice
vinegar, cola, beer
tomatoes
black coffee
urine
pure water
seawater
baking soda
Great Salt Lake
household ammonia
household bleach
sodium hydroxide
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Buffers in Biology

Health of organisms requires maintaining pH of
body fluids within narrow limits

Human blood normally 7.4 (slightly alkaline)

Many foods and metabolic processes add or subtract
H+ or OH- ions


Reducing blood pH to 7.0 results in acidosis

Increasing blood pH to 7.8 results in alkalosis

Both life threatening situations
Bicarbonate ion (-HCO3) in blood buffers pH to 7.4
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