the structure of Water

the structure of water , properties of water and biological significance

1. Properties of water and
biological significance
Vimal Priya subramanian

2. Structure of water
•Water is the chemical substance with chemical
formula H2O, one molecule of water has two
hydrogen atoms covalently bonded to a single
oxygen atom.
•Let us learn about the physical and chemical
properties of water.

3. •Closely observe the structure of a water
molecule. You will see one atom of oxygen and
two atoms of hydrogen.
•Each atom of hydrogen bonds covalently with
the atom of oxygen.
•So both atoms of hydrogen share one pair of
electrons with the oxygen atom.

4. Cont..
•Oxygen is a more electronegative element
in comparison to water.
•This results in an uneven distribution of
electron density.
•This gives the water molecule an angular
bent structure. The H-O-H bond has a slight
angle of about 104.5°. So it can be said that
water molecule is polar.
•It has a slight negative polarity near the
oxygen atom and slight positive charge
near both the hydrogen atoms.

5. Cont..
•The structure of the molecules of water in its frozen form i.e. ice is very unique. It forms a Lattice
Structure that does not generally occur naturally in any other substance other than ice.
•When water reaches its freezing point its atoms rearrange themselves in a very specific three-
dimensional pattern. The oxygen atom is surrounded by four hydrogen atoms. Two of these form O-
H bonds normally seen in water molecules.

6. Properties of Water
•The structure of the water molecule
creates weak attractions between the
oxygen end of one molecule and the
hydrogen ends of other water molecules.
•Even though these “polar” bonds are
relatively weak and are constantly
breaking and reforming, their existence
results in many special properties of water
compared to other substances on Earth.
These properties of water are largely
responsible for life on Earth.

7. Physical properties of water
•Water is a colourless and tasteless liquid.
•The molecules of water have extensive hydrogen bonds resulting in unusual
properties in the condensed form.
•This also leads to high melting and boiling points.
•As compared to other liquids, water has a higher specific heat, thermal
conductivity, surface tension, dipole moment, etc.
•These properties form the reason for its significance in the biosphere. Water
is an excellent solvent and therefore it helps in the transportation of ions and
molecules required for metabolism. It has a high latent heat of vaporization
which helps in the regulation of body temperature.

8. Physical properties of water
1.Chemical Formula
Chemical Formula of water as we
are all aware is H2O. The molecule
of water has covalent bonding
between Hydrogen and Oxygen
atoms. Two hydrogen atoms form
a bond with a single atom of
oxygen.
2.Appearance: Water is colorless,
odorless and tasteless liquid in its
natural state.

9. Cont..
•3.Freezing Point: The same
concept applies to the freezing
point of water as well. The
freezing point of water is 0 C.
4.Boiling Point:
•As we know, water has a boiling
point of 100 C.

10. Cont..
•Density: One unique property of
water is that in the sold state, it
is lense dense. Up to 4°C water’s
density does increase on
cooling. But after that point
water becomes less dense. This
is why ice floats in water,
•Viscosity: Water has high
viscosity due to very strong
intermolecular interactions
•Solvency: Water is an excellent
solvent. In fact, it is known as a
Universal Solvent. Due to a
water molecule’s polarity, it can
dissolve almost any substance.

11. Chemical properties of water
•Water reacts with a lot of substances to form different compounds. Some
significant reactions are as follows:
Amphoteric nature:
Water can act as both acid and base, which means that it is amphoteric in
nature.
Example:
Acidic Behaviour:H2O(l)+NH3(aq) ⇌H3O+(aq)+NH+4(aq)
Basic Behavior: H2O(l)+H2S(aq) ⇌H3O+(aq)+HS−(aq)

12. Redox reactions:
Electropositive elements reduce water to hydrogen molecule. Thus,
water is a great source of hydrogen.
Let us see an example in this case:
2H2O(l)+2Na(s)→2NaOH(aq)+H2(g)
During the process of photosynthesis, water is oxidized to O2. As water
can be oxidized and reduced, it is very useful in redox reactions.

13. Hydrolysis reaction
Water has a very strong hydrating tendency due to its dielectric
constant. It dissolves many ionic compounds. Some covalent and ionic
compounds can be hydrolyzed in water.

14. Biological significance of water
•Water possesses many unique qualities that are essential to maintaining
viable living conditions
•
•Approximately 70% of the cell’s internal environment (i.e. cytoplasm) is
water-based
•It is the only substance occurring naturally in all three states (solid, liquid,
gas) on the Earth’s surface
•It is required for the anabolic construction of organic molecules (via
condensation reactions)
•Water is an important medium for metabolic reactions as it is essential to
acid-base neutrality and enzyme function

15. Cont..
•From a Biological point of view, water is important for a number of
reasons:
•
•As a metabolite: Water is involved in many (bio)chemical reactions
inside cells –metabolism.
•
•For example, the chemical reactions of condensation and hydrolysis
involve the removal and addition of water, and water is essential for
the light-dependent reactions of photosynthesis.

16. Cont..
•As a solvent: many biological and inorganic chemicals dissolve in
water, and can be transported and react with other chemicals within
cells (and in laboratory test-tubes).