Title: Unique Properties of Water
Introduction: All living things are dependent on water. Your cells are mostly water
and they are surrounded mostly by water. Approximately 70% of the planet is
covered by water though most of it is salty and not drinkable
1- Structure of water and attraction
Structure of water
Water has two hydrogen atoms each joined to an
oxygen atom by a single covalent bond
Water is a polar molecule. This means that it has an
unequal charge. The hydrogen’s get pulled toward the
oxygen
Attraction
Water molecules are attracted to each other. The slight
negative charge at the oxygen end attracts the slightly
positive ends at the hydrogens. The bonds between
these water molecules are called hydrogen bonds
2- Waters life Supporting Properties
Cohesion
Cohesion is the tendency of molecules to stick to other
molecules of the same kind. Cohesion is much stronger
in water than in other liquids
Adhesion
Adhesion is the tendency of water molecules to stick to
other types of molecules
Why is this
important?
This is important for several reasons
-
Adhesion and cohesion help to keep large
molecules organized and operational in the cell
Transpiration – As water molecules are lost in
leaves during photosynthesis a partial vacuum is
formed in the vessels of the plant that carries
water. Adhesion and cohesion allow water to
travel against gravity and go from the roots to the
tips if the highest trees
Temperature
Moderation
Hydrogen bonds help water to resist temperature
changes. Think boiling water. Which heats up faster the
water or the pot?
-
Low density
Thermal energy – The total amount of energy
associated with the random movement of atoms
in matter
Temperature – is the average energy of the
random movement
When two substances differ in temperature heat
is transferred from the warmer object to the
cooler object (when you go into a pool you get
cold because you lose body heat into the cooler
pool)
Density is the amount of matter in a given volume of
space.
Density = mass / volume
As materials become solid the material in them tends to
become more compact – more dense. However this
does not occur in water. As water becomes a solid the
hydrogen bonds keep the molecules from becoming
tightly packed. Hence, ice becomes less dense than
liquid water – This allows ice to float
Universal Solvent
- Why is this so important to life on Earth?
A solution is a uniform mixture of two or more
substances, i.e., salt and water or lemonade and water
-
The substance that does the dissolving is called
the solvent
The substance that is dissolved is called the
solute
When water is the solvent it is called an “aqueous
solution”
Water is the main solvent in our cells
Water is considered the universal solvent because
many things dissolve in it. Including virtually
everything in our cells, allowing reactions to
occur, all ionic and many non-ionic compounds