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Unit 10: Properties of Water Study Guide
U2.2.1: Water molecules are polar and hydrogen bonds form between them (Oxford Biology Course
Companion page 68).
1. Describe the structure of an atom (in terms of protons, neutrons and electrons).
Atoms are composed of protons, neutrons and electrons. Protons have a positive charge,
neutrons have no charge (contain positive and negative that cancel), and electrons have a
negative charge. Protons and neutrons are found in the atomic nucleus. Electrons are
found in a cloud surrounding the nucleus. For example, the hydrogen atom:
2. Contrast ion with atom.
Atoms have no net charge because they have equal numbers of protons and electrons. If an atom gains
or loses an electron it will have a net charge and be called an ion.
 Gain an electron – net negative charge
 Lose and electron – net positive charge
3. Define anion and cation.
Anion: a negatively charged ion (has gained electrons)
Cation: a positively charged ion (has lost electrons) – “Itty bitty metal plussy kitty”
4. Contrast covalent, ionic and hydrogen bonds.
All bonding involves electrons or the charges that result from the transferiing of electrons.
Covalent bond: electrons are shared between two atoms
Ionic bond: attraction between a cation and an anion (no sharing of electrons)
Hydrogen bond: is actually an attraction between polar molecules with
hydrogen (not a true bond)
5. Write the molecular formula for water and draw the atomic structure of the
molecule.
Water is H2O. There are polar covalent bonds between each hydrogen atom and the
oxygen atom.
6. Describe the cause and effect of the polar nature of water.
Polar means a molecule (like water) has regions of slight charge due to the unequal sharing of electrons
in a polar covalent bond.
In water the oxygen has a greater pull on the electrons (higher electronegativity) than the hydrogen
atoms. As a result, there is unequal sharing of the electrons, with the electrons drawn closer to the
oxygen.
Because electrons have a negative charge, the unequal sharing of electrons within the bond leads to a
separation of positive and negative charge, “partial charges” denoted as δ+ and δ-.
7. Describe where and how water is able to form hydrogen bonds.
Water forms hydrogen bonds between the partial positive (δ+) hydrogen of one
water molecule and the partial negative (δ-) oxygen of another water molecule.
The δ+ and δ- attract.
NOS2.2: Use of theories to explain natural phenomena- the theory that hydrogen
bonds form between water molecules explain the properties of water (Oxford Biology
Course Companion page 69).
8. State why scientists cannot prove without a doubt that hydrogen bonds exist between water
molecules.
A scientific theory is a well-supported explanation of some aspect of the natural world that is
supported through repeated observation and experimentation. Because hydrogen bonds have yet to
be directly observed, their presence can not be proven. Hydrogen bonding does mathematically
(through molecular geometry), chemically, and observationally explain the properties of water.
U2.2.2: Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of
water (Oxford Biology Course Companion page 69).
9. Contrast adhesion with cohesion.
Adhesion: water attaching to a non-water structure through
hydrogen bonding or attraction to an ionic charge.
Cohesion: water attaching to another water molecule through
hydrogen bonding.
10. Outline an example of the cohesive property of water being of benefit to life.
 Water cohesion allows for surface tension. Insects such as the water strider are able to stay
on the surface of water.
 Water cohesion creates a chain of water molecules that allows for the transport of water
from the roots to the leaves of plants.
 Water cohesion is responsible for the high heat capacity of water, maintaining a relatively
temperature for stable internal and external environment for living organisms.
11. Outline an example of the adhesive property of water being of benefit to life.
Along with cohesion, adhesion is needed for water to move from the roots to the leaves
of plants. Water sticks to the sides of the xylem wall through adhesion.
12. Explain three thermal properties of water that are useful to living organisms.
Melting point and boiling point: water melts (0ºC) and boils (100°C) at relatively high
temperatures for a compound made of such light elements. This is due to the hydrogen
bonding between water molecules causing them to stick together and to resist being pulled apart
(which is what happens when ice melts and water boils to become a gas). Without this, water would
not be a liquid over much the surface of the Earth and we would not have an ocean.
High Specific heat (heat capacity): it takes a relatively large amount of heat energy to raise the
temperature of water. This is beneficial because the temperature of large bodies of water remains
relatively constant, protecting them from possibly lethal temperature fluctuations.
Density: because of the hydrogen bonding structure, solid water (ice) is less dense than liquid water.
So ice floats on top of lakes like a blanket, insulating the living organisms living in the lake.
13. Outline a benefit to life of water's high specific heat capacity.
14. Outline a benefit to life of water's high latent heat of vaporization.
Is a measure of how much energy needs to be added to vaporize water. It takes an unusually high
amount of heat energy to vaporize water because hydrogen bonds must be broken in order for
water molecules to fly off as a gas. As the water evaporates, the surface left behind becomes cooler.
This is called evaporative cooling. It allows organisms to cool with sweating so a consistent body
temperature is maintained.
15. Outline a benefit to life of water's high boiling point.
16. Explain why is water such a good solvent.
Water is a good solvent because it can form hydrogen bonds with a variety of different substances.
Water is called “the universal solvent” because it dissolves more substances than any other liquid.
17. List the types of molecules that water will dissolve.
Substances that water dissolves must be either polar or charged ionic compounds.
A2.2.1: Comparison of the thermal properties of water with those of methane (Oxford Biology Course
Companion page 71).
18. Compare and contrast the physical properties of methane and water.
Methane
Oxygen
Density
Less
More
Heat Capacity
Less
More (takes more energy to
change temperature)
Melting Point
Boiling Point
-182 ºC
-160 ºC (typically found as gas
on the surface of the Earth)
0 ºC
100 ºC
19. Explain why water and methane have different thermal properties based on their molecular
structures.
The major differences between methane and water that is responsible for their different properties
is the polarity of the covalent bond in water.
Water has a polar covalent bond with unequal sharing of electrons. Leads to
partial charges δ+ and δ- = STICKY
Methane is a nonpolar covalent bond with equal sharing of electrons so
no partial charges result = NOT STICKY
A2.2.2: Use of water as a coolant in sweat (Oxford Biology Course Companion page 72).
20. Explain sweating as a mechanism to cool the body.
Sweat is mostly water. When the water evaporates from the surface of the skin, it takes heat with it.
With the loss of the heat energy, the skin feels cooler.
U2.2.3: Substances can be hydrophilic or hydrophobic (Oxford Biology Course Companion page 70).
21. State that polar and ionic molecules are hydrophilic.
Polar and ionic molecules are hydrophilic because water’s partial charges are attracted.
Glucose is hydrophilic because it has
many polar covalent bonds between O
and H. Water can hydrogen bond to the
resulting δ+ and δ-
Ions are hydrophilic because water is attracted to the negative and positive charges.
22. State that non-polar, non-ionic molecules are hydrophobic.
There are no full or partial charges for the δ_ oxygen of water and/or the δ+ hydrogen of water to be
attracted.
“Nothing
here for me
I’m a
hydrophobic
hydrocarbon.”
23. Given a diagram of a molecular structure, determine if the molecule is hydrophilic or hydrophobic.
First, look for indication of a charge, notd by a + or – symbol. If there is a charge, the molecule will be
hydrophilic.
Then look for the presence of polar covalent bonds. For our purposes, these will primarily be
between an O and an H (sometimes between an N and an H).
Water is attracted to the resulting partial charges, making molecules with many –OH groups
hydrophilic.
If there are no charges (full or partial) then the molecule is hydrophobic. In our class, these will
usually be hydrocarbons.
A2.2.3: Modes of transport of glucose, amino acids, cholesterol, fats, oxygen, and sodium in blood in
relations to their solubility in water (Oxford Biology Course Companion page 72).
24. State if the following molecules are hydrophobic or hydrophilic: glucose, amino acids, cholesterol,
fats, oxygen, and sodium chloride.
Hydrophilic: glucose (many –OH); amino acids (although variable, many amino acids have polar or
ionic side chains), sodium chloride (ions)
Hydrophobic: some amino acids, cholesterol (primarily a non-polar hydrocarbon), fats (primarily a
nonpolar hydrocarbon, oxygen (O2, nonpolar)
25. Outline the mechanism of transport in the blood of the following molecules: glucose, amino acids,
cholesterol, fats, oxygen, and sodium chloride.
Blood is primarily water. Because they are hydrophilic, the following molecules can dissolve and be
directly transported in the blood: glucose, many amino acids, salt ions (Na+ and Cl-)
Because they are hydrophobic, the following molecules must be transported in the blood bound to
transport molecules or packaged into water soluble sacs:
 cholesterol, fats - Packaged into amphipathic sacs (micelles) with hydrophobic interiors and
hydrophilic interiors.

Oxygen – transported bound to hemoglobin molecule.