The ability of water to form hydrogen bonds gives it amazing properties including: ability to dissolve hydrophilic (ionic and polar) but not hydrophobic (nonionic, nonpolar) molecules so as to be the "universal solvent," liquid state over large earthly temperature range, high heats of fusion and vaporization, high specific heat, high surface tension, cohesion and adhesion, lower density as solid, low viscosity, equal ionization into proton donor and acceptor for neutral pH. These properties make life on earth possible

1. Water
Without Water
There Can Be
No Life!
© 2022, Veronica Drantz PhD

2. The Amazing Properties of Water
• Are due to
its ability
to form
hydrogen
bonds

3. Hydrogen Bonding Ability of Water
• Is due to two features
• The polar covalent bonds that bind the
hydrogen atoms to the oxygen atom
• The asymmetric distribution of these polar
covalent bonds

4. Polar
Covalent
Bonds
• The polar covalent bonds
bind the hydrogen atoms to
the oxygen atom
• The oxygen is more
electronegative than the
hydrogens
• Oxygen pulls on the bond
electrons harder
• Oxygen atom acquires two partial
positive charges
• Each hydrogen atom acquires a
partial negative charge
• These polar covalent
bonds are ~1/3 ionic and
2/3 covalent in character

5. Water Is a Polar Covalent
Compound

6. Asymmetric
Distribution
of Polar
Covalent
Bonds
• The asymmetric
distribution of these
polar covalent bonds
creates the V shape of the
water molecule
• Causes the two partial
positive charges to be on
the hydrogen side and the
two partial positive
charges on the oxygen
side of the molecule
• Causes water to be a
dipole

7. Water Molecules
Are V-shaped and Polar

8. Dipole-dipole hydrogen bonds
are the bonds that water
molecules form with each other
or with other polar molecules
Ion-dipole hydrogen bonds
are the bonds that water forms
with ions
Water Forms Two Kinds of Hydrogen Bonds

9. • Hydrophilic
means
“water-
loving”
• Hydrophobic
means
“water-
hating”
Hydrophilic Versus
Hydrophobic Substances

10. Hydrophilic Substances
Are Water-soluble
• Form hydrogen bonds with water
• Ionic compounds and moieties
• Polar organic molecules and moieties
• Hydrophilic substances are lipophobic
(“fat-hating”)

11. Hydrophobic Substances
Are Water-insoluble
• Do not form hydrogen bonds
• Hydrocarbon molecules and moieties
• Alkanes
• Oils
• Fats
• Greasy substances
in general
• Hydrophobic
substances are lipophilic”
(“fat-loving”)*
“Hydrophobic is often used interchangeably with lipophilic, "fat-loving". However, the two terms are not synonymous. While hydrophobic substances are
usually lipophilic, there are exceptions, such as the silicones and fluorocarbons.” https://en.wikipedia.org/wiki/Hydrophobe

12. • Amphipathic
means “both
hydrophilic and
hydrophobic”
• Also called
amphiphilic
• Molecules that
contain both
polar and
hydrocarbon
moieties (e.g.,
phospholipids)
Amphipathic Substances Are
Water-soluble and Lipid-soluble

13. Phospholipids Are Amphiphilic

14. Biological
Membranes
Have Hydrophobic Interior and
Hydrophilic Surfaces

15. Many Functional Groups Of Organic
Molecules Are Hydrophilic
• Are polar and/or ionic
• Form dipole-dipole or ion-dipole
hydrogen bonds with water
HYDROPHILIC FUNCTIONAL GROUPS IN BIOMOLECULES
Hydroxyl (alcohol) group sugars
Carboxyl (acid) group fats, amino acids
Ketone (carbonyl) group some sugars
Aldehyde group some sugars
Amine (amino) group amino acids, proteins
Sulfydryl group some amino acids, proteins
Phosphate group phospholipids, nucleotides, nucleic acids

16. Biomolecule Functional Groups
TABLE 2-2 Common Functional Groups and Linkages in Biomolecules
Common covalent linkages and functional groups confer distinctive chemical properties on the molecules of which they are a part.

17. Dipole-Dipole Hydrogen Bonds
Between Water
& Polar Organic Molecules
FIGURE 2-8 Hydrogen bonding of water with itself and with other compounds.
• When the one covalent bond that a H atom can form is to an electronegative atom such as the O in water (donor atom), the
H can form another weak interaction with an acceptor atom, such as an oxygen or nitrogen atom that has a pair of
nonbonded electrons.
• The length of the donor-H bond becomes longer as the acceptor pulls the H away from the donor. In the strongest hydrogen
bond, the donor-H-acceptor lie in a straight line, but weaker nonlinear hydrogen bonds can form.
• (a) In liquid water, transient hydrogen bonds between waters create a dynamic network.
• (b) Water forms hydrogen bonds with alcohols and amines, which solubilizes compounds.
• (c) The peptide group and the ester group, which are present in many biomolecules, form hydrogen bonds with water or
other polar groups to stabilize molecular structures and interactions.

18. Properties of Water
• Universal solvent
• High melting point and high boiling point with
large temperature range for liquid state
• High heat of fusion
• High heat of vaporization
• High specific heat
• High surface tension
• Cohesion and adhesion
• Lower density as solid
• Low viscosity
• Equal ionization into proton donor and acceptor

19. “Universal solvent”
• Ionic solutes: ion-dipole H bonding
• Polar molecular solutes: dipole-dipole H bonding
(see above table)
TABLE 2-2 Common Functional Groups and Linkages in Biomolecules
Common covalent linkages and functional groups confer distinctive chemical properties on the
molecules of which they are a part.

20. Wide Temperature Range for
Liquid State
• High melting point (0 oC)
• High boiling point (100 oC)
• Wide range of
temperatures in which
water is in liquid state
(0 oC – 100 oC)

21. Water Ought To Be A Gas!
• By molecular weight (MW), water ought to be a
gas:
• CO2 (MW=44), O2 (MW=32), CO (MW=28), N2
(MW=28), CH4 (MW=18), and H2 (MW=2) are all
gasses at room temperature.
• Water (MW=20) is a liquid. Why?
• Because water molecules display cohesion and
thus have a much reduced tendency to fly off into
the overlying atmosphere than these other listed
molecules

22. It Takes A Lot Of
Energy
To Heat Water
• High heat of fusion
• 80 cal/g at 0 oC
• High heat of
vaporization
• 539 cal/g at 100 oC
• 580 cal/g at 20 oC
www.crrel.usace.army.mil/permafrosttunnel/1g4

23. Water Has A High Heat Of
Vaporization (Evaporation)
• 539 cal/g at 100oC
• 580 cal/g at 20oC
• Because it also involves the breaking of
hydrogen bonds, water resists vaporizing
(evaporating)
• Consequently, it takes a lot of heat to
evaporate water
• This high heat of vaporization is also
utilized by organisms as a cooling process,
e.g., sweating or panting

24. High Specific Heat
• High specific heat of liquid water
• 1 cal/g oC
• By definition, a temperature increase is
an increase in the velocity the
molecules and atoms making up a
substance
• Because of cohesion, water molecules resist
increasing their motion. (This is another way of
saying that is water molecules resist the net
breaking of hydrogen bonds). Consequently,
water resists heating; water has a very high
specific heat

25. Bodies of Water Resist
Temperature Change
• This tendency to not want to change
temperature causes resistance to radical
temperature swings
• Causes bodies of water (e.g., a lake) to
strongly resist rapid changes in
temperature
• This temperature buffering capacity of
water is taken advantage of to a great
extent by organisms

26. Surface Tension
•The molecules at the surface do not have other like
molecules on all sides of them and consequently they
cohere more strongly to those directly associated with
them on the surface
• This forms a surface "film" which makes it more difficult
to move an object through the surface than to move it
when it is completely submersed.
hyperphysics.phy-astr.gsu.edu/Hbase/surten.html

27. Surface Tension
• Surface tension is typically measured in
dynes/cm, the force in dynes required to
break a film of length 1 cm
• Equivalently, it can be stated as surface
energy in ergs per square centimeter
• Water at 20°C has a surface tension of
72.8 dynes/cm compared to 22.3 for
ethyl alcohol and 465 for mercury
hyperphysics.phy-astr.gsu.edu/Hbase/surten.html

28. Water Has A
High Surface
Tension
• The surface tension of water
is 72 dynes/cm at 25°C. It
would take a force of 72
dynes to break a surface film
of water 1 cm long
• The surface tension of water
decreases significantly with
temperature as shown in the
graph
• Hot water is a better cleaning
agent because the lower
surface tension makes it a
better "wetting agent" to get
into pores and fissures rather
than bridging them with
surface tension
• Soaps and detergents further
lower the surface tension hyperphysics.phy-astr.gsu.edu/Hbase/surten.html

29. Video – Surface Tension and
Surfactant
http://www.springerpub.com/media/spring
er-downloads/Shubert-3rd-
Edition/7_2_Surfactants-and-Surface-
Tension.mp4

30. Water Molecules Are
Cohesive And Adhesive
• Cohesion
• The attraction of one water molecule to another
resulting from hydrogen bonding
• By placing a drop of water on a surface you can directly
observe cohesion in the resistance that water droplet
shows to wetting, i.e., water clumps up in a pile despite
being a liquid, rather than spreading out over the
surface. (Note that wetting is less likely to occur in the
absence of adhesion to a wet surface)
• Adhesion
• Adhesion is similar to cohesion except adhesion
involves the attraction of a water molecule to a non-
water molecule
• Cohesion is thus a special case of adhesion

31. • Capillary action is the result of adhesion and surface
tension
• Adhesion of water to the walls of a vessel will cause an
upward force on the liquid at the edges and result in a
meniscus which turns upward
• The surface tension acts to hold the surface intact, so
instead of just the edges moving upward, the whole
liquid surface is dragged upward
Capillary Action

32. Water Is
Cohesive
and
Adhesive

33. Water Is Less Dense As Solid
Than As Liquid
• Maximum density at 3.98 oC
• Ice floats above liquid water because is
less dense as solid than as liquid
• The density of water is actually less than it
could otherwise be because hydrogen bonded
water is packed slightly less favorably than
could be achieved without hydrogen bonding
• Ice represents a maximal hydrogen bonding of
water, indeed the crystallization of water into
the structure formed upon hydrogen bonding.
Thus, ice occupies a greater volume per unit
mass and, consequently, floats on water

34. Ice Floats

35. Ice Crystal
•Ice represents a
maximal hydrogen
bonding of water
•High pressures
tend to inhibit the
solidification of
water, so ice forms
at top of liquid
waterr

36. General Phase Diagram Versus
Phase Diagram for Water
In water’s diagram, the slope of the line between the solid and liquid states is negative rather than positive. The reason is that
water is an unusual substance in that its solid state is less dense than the liquid state. Ice floats in liquid water. Therefore, a
pressure change has the opposite effect on those two phases. If ice is relatively near its melting point, it can be changed into
liquid water by the application of pressure. The water molecules are actually closer together in the liquid phase than they are in
the solid phase. https://courses.lumenlearning.com/cheminter/chapter/phase-diagram-for-water/
http://learn.chem.vt.edu/tutorials/Isproperties.html
https://courses.lumenlearning.com/cheminter/chapter/phase-diagram-for-water/

37. Viscosity
• Viscosity of a liquid is a measure of
its inability to flow, and this is
measured in N s m-2 (SI Units) or
poise (P) or centipoise (cP)
• 1 P = 0.1 N s m-2
• 1 cP = 0.001 N s m-2
• Viscometers are used to measure
viscosity

38. Viscosity of Water
Depends on the Temperature
Temperature (°C) Viscosity (cP)
20 1.002
40 0.653
60 0.467
80 0.355
100 0.282
•Viscosity decreases as temperature increases

39. Viscosity and Surface Tension of
Various Liquids at 293 K
Common
liquid
Viscosity
cP
Surface tension
N m-1
Diethyl ether 0.233 0.0728
Chloroform 0.58 0.0271
Benzene 0.652 0.0289
Carbon
tetracholoride
0.969 0.0270
Water 1.002 0.0728
Ethanol 1.200 0.0228
Mercury 1.554 0.436
Olive oil 84 -
Castor oil 986 -
Glycerol 1490 0.0634
Glasses very large -

40. Water Ionizes into an Equal Number
of Positive Hydronium Ions And
Negative Hydroxide Ions
2H2O(l) →H3O+(aq) + OH-(aq)

41. H2O Can Act As Both A Proton
Donor And Acceptor For Itself
• Water undergoes autoionization (dissociation) in
which a proton is transferred from one water
molecule to another
• This dissociation produces one hydronium ion
(H3O+) and one hydroxide ion (OH-)
2H2O(l) H3O+(aq) + OH-(aq)
• This equilibrium can also be expressed as
H2O(l)  H+(aq) + OH-(aq)
• In the above equilibrium, water acts as both an
acid and a base
• The ability of a substance to act as either an acid
or a base is known as amphoterism

42. The Concentrations of H3O+ and OH-
Produced By the Dissociation of Water
Are Equal
• The corresponding equilibrium expression for this
would be:
• KC = {[H+][OH-] / [H2O]}
• In pure water at 25oC, [H2O] = 55.5 M
• This value is relatively constant in relation to the
very low concentration of H+ and OH- (1 x 10-7 M).
• Therefore, KC = [H+][OH-] / 55.5 M
• Rearranging gives: KC (55.5 M) = [H+][OH-] = Kw
• So now we can eliminate [H2O] from the equation
and we are left with: KW = [H+][OH-]
• Where KW designates the product (55.5 M) KC and is
called the ion-product constant for water
• At 25oC, KW is equal to 10-14

43. The Ion-product Constant Always
Remains Constant At Equilibrium
• Consequently, if the
concentration of either H+ or
OH- rises, then the other must
fall to compensate
• In acidic solutions, [H+] > [OH-]
• In basic solutions [H+] < [OH-]
FIGURE 2-25 Some pH values for common solutions.
• H+ and OH- are dissociation products of H2O and present in all aqueous solutions
(pure water, pH 7).
• The pH of an aqueous solution is the negative log of the hydrogen ion concentration.
• pH values for most intracellular (cytoplasm 6.6-7.2) and extracellular biological fluids
are near 7 and are carefully regulated to permit the proper functioning of cells,
organelles, and cellular secretions.
• pH values of intracellular organelles may be 4.5 (lysosome). Stomach pH is 1-2.
• Changes in pH can regulate cellular activities.

44. Video - pH
http://www.springerpub.com/media/spring
er-downloads/Shubert-3rd-
Edition/9_1_pH.mp4

46. Earth