Unit 2:
All Biology is Chemistry
Lesson 3: Water & Solutions
Drill
19 October 2009
K-W-L
 With a partner, complete the first two columns of the
chart:
What do I
KNOW about
water
What do I WANT What have I
to know about
LEARNED about
water
water
Objectives
At the conclusion of this lesson students will be able to:
1.
2.
3.
4.
5.
6.
7.
8.
describe the structure of a water molecule
explain what is meant by a molecule’s polarity
explain why hydrogen bonds form between water molecules
identify common properties of water that result from
hydrogen bonding
identify the difference between solutes and solvents in
solutions
differentiate between acids and bases
understand how to read and interpret the pH scale
define a buffer and explain their role in living systems
The Structure of Water
 Composed
of two hydrogen atoms covalently
bonded to an oxygen atom.
Oxygen
Polarity
 However,
oxygen and
hydrogen do not share
electrons equally.

Oxygen
8p
8n
As a result…
• Oxygen atom has a partial
negative charge (δ-)
• Hydrogen atoms have partial
positive charges (δ+)
• Total charge of the water
molecule is still neutral
Obj. 1
δ-
δ+
δ+
Space filling model of a
water molecule
Hydrogen Bonding

Water molecules have an uneven distribution of
charge
 Positively charged region (δ+) of one water
molecule is attracted to the negatively charged
region (δ-) of a nearby water molecule.
 This attraction is called a hydrogen bond.
δ-
δ+
δ+
δ-
δ+
δ+
Hydrogen Bonds
 Weak
forces of attraction
 Form, break, and reform frequently
 Number of hydrogen bonds in water depends
on its state (solid, liquid, or gas)
Significance of Hydrogen Bonds
 Account







Obj. 2
for the unique properties of water
Cohesion
Surface tension
Adhesion
Ability to absorb a relatively large amount of heat
energy
Ability to cool surfaces through evaporation
Solid state is less dense than its liquid state
Ability to dissolve many substances
Cohesion
 Cohesion
- an attractive force that holds
molecules of a single substance together
Surface tension
 Tendency
of water molecules on the edges of a
water droplet to attract inward toward other
water molecules thus producing a “skin”
Adhesion
 Adhesion
– attractive force between two
particles of different substances
Temperature Moderation
 Temperature
is a measure of
heat which is a form of energy


Water can absorb large amounts
of energy as heat for its
molecular size
Water has the highest specific
heat of any common substance.
Specific heat is the heat required to raise the temperature of one gram of a substance one
degree Celsius.
Effects of a High Specific Heat
 Water
can absorb/release a large quantity of
heat without a large change in temperature
•Moderates coastal
climates
•Reduces dramatic
day-night
temperature
fluctuations
Evaporative Cooling
As water evaporates,
the surface of the water
that remains behind
cools.
 Principle behind
sweating to maintain
body temperature in
land animals

Density of Ice





Angle of hydrogen bonds
causes ice crystals to have lots
of open space
Open space leads to low
density
As a result, ice floats!
Ponds & lakes freeze from top
to bottom.
Ice insulates deeper water
from colder air.
Ice crystal
Liquid water
Glossary
adhesion – an attractive force between two particles
of different substances
 cohesion – an attractive force that holds molecules of
a single substance together
 hydrogen bond – force of attraction between a
hydrogen molecule with a partial positive charge and
another atom or molecule with a partial or full
negative charge
 polar compound – a compound with an uneven
distribution of charge within the molecule

Work Cited
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"Graduated cylinders." 10 mL graduated cylinder. 1995-1995. NT Curriculum Project, UWMadison. 19 Oct 2006 <www.uwplatt.edu/.../volume/gradcyl/gradcyl.htm>.
Lower, Stephen. "H2O: a gentle introduction to the structure of water." 16 May 2005. Dept of
Chemistry, Simon Fraser University. 19 Oct
2006<http://www.chem1.com/acad/sci/aboutwater.html>.
Microsoft Corporation, "Hydrogen Bonding in Water." MSN Encarta. 19 Oct 2006
<http://encarta.msn.com/media_461547672_761563983_1_1/Hydrogen_Bonding_in_Water.html>.
Nave, R. "Water." Hyperphysics Chemistry. 19 Oct 2006 <hyperphysics.phyastr.gsu.edu/.../water.html>.
Saloutos, Peter. "Surface Tension in Water Droplets." MSN Encarta. 19 Oct 2006
<http://encarta.msn.com/media_461560536_761563983_1_1/Surface_Tension_in_Water_Droplets.html>.
"Specific Heat." 1999. 19 Oct 2006 <www.chem.uiuc.edu/webFunChem/heat/heat.htm>.
"Sunset Island Wedding." Miami Skyline. 31 Aug 2006. 19 Oct 2006
<www.weddingsbythesea.net/sunset.htm>.

“Surface tension” Molecules. Retrieved on 19 Oct. 2006 from <http://universereview.ca/option2.htm>.