Four emergent properties of water
• ALL ARE A RESULT OF HYDROGEN
BONDING
 H-bonds = Hydrogen atom of a molecule is
covalently bonded to an electronegative atom
of that molecule and bonded to an
electronegative atom of ANOTHER MOLECULE;
individually, are weak.
 Polar covalent bond holds H atom to O
atom WITHIN a water molecule. O shares eunequally ~ highly electronegative.
2 Water Molecules with the Bonds
1.Cohesion
• Collectively, H-bonds hold water
molecules together.
• Cohesion – due to constant breaking
and reforming of H-bonds. Makes
water a very structured liquid.
Related to cohesion:
a) Capillary Action = Helps plants
fight gravity. As water leaves the
top of the plant as vapor, the
water molecules remaining at
the top, pulls on the water
molecules below as new Hbonds reform.
b)Adhesion = two different
substances clinging together.
Example: Water adhering to the
cell of the xylem also helps
counter act gravitational pull of
water downward in a plant.
c)Surface Tension = a property
of the surface of liquid that
allows it to resist “breaking.”
This characteristic allows
animals to “walk on water” even
though they have a greater
density than water.
2.High specific heat and heat of
vaporization
• Specific Heat = the amount of heat that
must be lost or absorbed for 1g of a
substance to change 1C
Specific heat of water = 1cal/g/C
Even though heat is breaking H-bonds, they
reform quickly; makes water temp. difficult to
change.
Relative to planet’s temp.? Body temp.?
• Heat of vaporization = the amount of
heat a liquid must absorb for 1g of it
to turn into vapor.
- As water evaporates, the remaining
liquid cools because heat is
released with the vapor =
evaporative cooling
Helps plants stay cool on warm days
Helps body cool when sweating
- Humidity = high concentration of
water in the air.
Discomfort comes from water
vapor in the air inhibiting
evaporation of sweat.
3.Insulation of Bodies of Water by
Floating Ice
Water expands when frozen; unlike
other substances.
- Since molecules barely move in solid state,
few H-bonds break; forms strong lattice.
- Makes solid form less dense than liquid state
= floating
The floating water insulates the water below
allowing life to exist under ice.
4.Solvent of Life
Background you should know:
Solution = homogenous mixture of
two or more substances.
Aqueous solution = a solution where
water is the solvent.
Solute = substance being dissolved;
Solvent = doing the dissolving.
Water is a good solvent due to its
polarity.
 Weak H-bonds constantly breaking
exposes the + and - ends of water a
molecule.
 The O (-) of water attracts cations of
an ionic compound; H (+) of water
attract the anions. The solute is
ripped apart.
Hydration Shell
Water molecules surround the ion
of the dissolved solute (with their
respective oppositely charged
ends) and shield them from the
other ion of the solute it was
bonded with not allowing the ionic
bond to reform.
Ex:
NaCl with hydration shell
o Both ionic and other polar
molecules have an affinity for
water = Hydrophilic
o Non-polar molecules do not
have an affinity for water =
Hydrophobic