INTERMOLECULAR FORCES
Dipole-to-dipole forces—Polar molecules.
+
-
+
-
+
- +
-
Polar molecules are also attracted by "
dipole-dipole attractions. The strength of "
attraction is stronger between polar molecules "
than between nonpolar molecules of the same size.
INTERMOLECULAR FORCES
Hydrogen Bonding"
• HF, or molecules that have
OH or NH groups have
particularly strong
intermolecular attractions."
– Unusually high melting and
boiling points."
– Unusually high solubility in
water."
• This kind of attraction is
called a hydrogen bond.
PHASE DIAGRAM "
Evaporation/Condensation
• In an open container, as you heat a
liquid the average kinetic energy of
the molecules increases, giving
more molecules enough energy to
escape the surface."
– So the rate of evaporation increases."
• Eventually, the temperature is high
enough for molecules in the interior
of the liquid to escape. A
phenomenon we call boiling."
Melting/Freezing"
• The amount of heat needed to melt one mole of a solid
is called the heat of fusion (Melting)."
– ∆Hfus"
– Fusion is an old term for heating a substance until it melts, it
is not the same as nuclear fusion."
• Since freezing (crystallization) is the opposite process
of melting, the amount of energy transferred is the
same, but in the opposite direction."
Sublimation"
• Sublimation is a physical
change in which the solid
form changes directly to the
gaseous form."
– Without going through the
liquid form."
• Like melting, sublimation is
endothermic."
Water Chemistry
All living organisms are dependent on water."
"
The structure of water is the basis for its
unique properties."
"
The most important property of water is the
ability to form hydrogen bonds.
COOLING OF EARTH"
HYDROLOGICAL CYCLE"
"WATER EXISTS ON EARTH IN"
SOLID, LIQUID AND SOLID"
Water Chemistry
Within a water molecule, the bonds between oxygen
and hydrogen are highly polar."
Partial electrical charges develop:"
- oxygen is partially negative"
- hydrogen is partially positive"
All living organisms are dependent on water."
The structure of water is the basis for "
its unique properties."
The most important property of water "
is the ability to form hydrogen bonds.
5-3
Water dissolves salts by surrounding the atoms in the
salt molecule and neutralizing the ionic bond holding
the molecule together. Dissolved salts form cations
(positively charged ions) and anions (negatively
charged ions)."
The process of water surrounding an ion is called hydration.
Properties of Water
HYDROGEN BONDING"
–The slightly negative regions of one molecule are "
–attracted to the slightly positive regions of nearby "
–molecules, forming a hydrogen bond."
HYDROGEN BONDING"
–Each water
molecule !
can form hydrogen !
bonds with up to !
four neighbors."
Hydrogen Bonding
• + attracted to –!
• Each H2O is bonded
to its nearest
neighbor"
Association energy of"
Hydrogen bond is"
About 10 kca/mole "
About 1/10 of O-H bond)"
Hydrogen bonding is responsible for many of "
the unique properties of water because more "
energy is required to break the hydrogen "
bonds and separate the water molecules."
These properties are:"
• Boiling and melting points,"
• Density of ice and water"
• Specific heat"
• Solvation"
• Surface tension"
BOILING POINT OF WATER"
Properties of Water
1. Water has a high specific heat."
"- A large amount of energy is required to
change the temperature of water."
2. Water has a high heat of vaporization."
"- The evaporation of water from a surface
causes cooling of that surface.
Properties of Pure Water
• Latent heat of fusion:
water requires a large loss of
energy to pass from liquid to
solid phase. "
• Reverse is true for latent heat
of vaporization."
• Meaning: large bodies of
water resist changes in
temperature, life processes
remain constant."
• Has implications towards
system design (takes long time
to heat water)."
More than 62% of our body i s water. The percentage depends on the age of the
human being- in children this percentage is higher than in an adult s body. Our
daily consumption of water is approximately 2.7 L. This amount of water may come
from a variety of sources: food, metabolism, drinking, and etc.
H2O regulates HOMEOSTASIS (The ability or tendency of an organism or
cell to maintain internal equilibrium by adjusting its physiological
processes) and the body is not able to function properly without it.
BODY TEMPERATURE"
Temperature (C) !Symptoms !!
28 "muscle failure""
30 "loss of body temp. control ""
33 "loss of consciousness ""
37 "normal""
42 "central nervous system breakdown""
44 "death ""
ADH = Anti Diuretic Hormone"
Water content of
the blood HIGH
Water content of
the blood LOW
Too much water drunk
Too much salt
or sweating
Brain
produces
More ADH
Brain
produces
Less ADH
Water content
of the blood normal
High volume of water
reabsorbed by kidney
Urine output
LOW
(small volume of
Concentrated urine)
Low volume of water
reabsorbed by kidney
Urine output
HIGH
(large volume of
dilute urine)
Body will loose 1 liter of water per hour of running "
IMPACT OF WATER
PROPERTIES ON THE
ENVIRONMENT"