2. Water: The Facts
Water is possibly the most important
compound in living organisms.
Water consists of 1 atom of oxygen
combined with 2 atoms of hydrogen.
Water makes up 70 to 95 percent of most
organisms.

3. What are the characteristics of
water?
1. Water is polar.
2. Water molecules attract other water
molecules. This property is cohesion.
3. Water displays adhesion.
4. Water expands when it freezes.

4. Water is Polar
A polar molecule has
an unequal
distribution of
charge-each
molecule has a
positive end and a
negative end.
All polar substances
are attracted to other
polar substances.

5. Why is this polarity important?
Polar water molecules attract other
water molecules as well as ions and other
polar molecules.
Because of this attraction, water can
dissolve many ionic compounds, such as
salt and polar molecules like sugar.

6. How do water molecules
attract?
Water molecules form hydrogen bondshydrogen bonds.
Hydrogen bonds are weak bonds that
form between the positively charged
hydrogen atoms of one water molecule
and the negatively charged oxygen atoms
of another water molecule.
This ability of water molecules to stick
together is called cohesioncohesion.

7. Also due to its polarity…
Water displays the property of adhesionadhesion
which is the ability of one substance to
cling to another.
Examples of adhesion include water’s
ability to creep up thin tubes. Plants
show this property when they send water
from the soil up through their tissues.

8. And finally…water expands when it
freezes.
Because of this
property, ice is less
dense than liquid
water.
This property can be
seen when ice forms
and floats on the
surface of a pond.