Water and Aqueous Systems
http://www.sumanasinc.com/webcontent/animations/content/
propertiesofwater/water.html
The Water Molecule
¥  Polar
molecule
¥  Covalent Bonds
between H and O
¥  Considered to be the
“universal solvent”
Solutions: contain a
solute and solvent
¥  Solute: gets dissolved
¥  Solvent: does dissolving
¥ 
Polarity
¥  Water
is a solvent because it’s polar
¥  Oxygen atom in the water molecule has a
high electronegativity
Electrons shared by the hydrogen and oxygen
atoms are more attracted to the oxygen
¥  Unequal attraction of electrons generates partial
electric charges within the water molecule
¥  Oxygen atom has partial negative charge, and the
hydrogen atoms have a partial positive charge
¥ 
Polarity: DRAW THIS PICTURE
Hydrogen Bonding
Attractive interaction
between a hydrogen atom
and an electromagnetic
atom (O, N,F)
¥  Hydrogen bonding is
responsible for many of the
unique properties of water
such as:
¥  high surface tension
¥  low vapor pressure
¥  lower density in the
solid form than in the
liquid
¥  high specific heat
¥ 
Surface Tension…
¥ 
Is the result of unbalanced forces which
exist on the surface of a liquid
Submerged molecules are tugged in all directions
¥  But molecules on surface have no pull upward on them
¥ 
Surface tension is an inward force that causes
the surface to behave as a skin
¥  Surface tension causes water to form nearly
spherical droplets
¥ 
Surface Tension
¥  Surface
tension causes water to form nearly
spherical droplets
Surface Tension of Water
http://quest.nasa.gov/space/teachers/microgravity/image/66.gif
Capillarity
¥  Tendency
for a liquid to rise spontaneously in a
small tube
¥  Unbalanced forces experienced by surface
molecules are alleviated by polar water molecules
that are also attracted to tubes (Adhesion)
¥  Combination of forces pulls a film of water
onto waters of tubes and water molecules that
hang together (cohesion) move up into the tube
Water’s Low Vapor Pressure
¥  Because
of hydrogen bonds holding the water
molecules together, molecules have low
tendency to break free from the surface into
the vapor phase
Density of Water
¥  Ice
has a lower
density than liquid
water
¥  Maximum density of
water happens at
4OC (not as ice!)
Density of Water
¥  Most
substances are denser in solid state than in
liquid state
¥  In solid state, each molecule of water is hydrogen
bonded to four other water molecules
¥ 
Forms an open crystal lattice with open space
¥  When
ice melts, hydrogen bonds break
Lattice collapses
¥  Water molecules move closer together and occupy less
space
¥ 
Specific Heat of Water
¥  Water
has an extraordinarily high specific heat,
or capacity to absorb energy
¥  Specific heat is measured as the amount of
energy required to raise the temperature of
one gram of a substance by one degree
Celsius
¥  Water’s specific heat is unusually high because it
contains many hydrogen bonds
¥ 
A large amount of energy is needed to break the
hydrogen bonds between the molecules before heat
is transferred
Review Questions
¥  Write
the chemical equation for water, and
draw a stick model of a water molecule.
¥ 
H2O
¥  What
¥ 
causes surface tension?
Unbalanced forces
Review Questions
¥  What
property is responsible for water
getting to the leave in the tops of the tallest
trees against the force the gravity?
¥ 
Capillary Action (capillarity)
¥  Why
¥ 
does ice float on water?
Water is less dense in the solid state than in liquid
state
Review Questions
¥  What
kind of bond holds hydrogen to the
oxygen in ONE water molecule?
¥ 
COVALENT
¥  What
kind of bonds can hold two separate
water molecules together?
¥ 
HYDROGEN BONDS