2. water
• Water is the most abundant substance in
living systems, making up 70% or more of the
weight of most organisms. The first living
organisms doubtless arose in an aqueous
environment, and the course of evolution has
been shaped by the properties of the aqueous
medium in which life began.
3. Characteristics of Water
• Water is a liquid at standard temperature and
pressure (25 degrees Celsius and 1 atm, for
liquids).
• Water is tasteless and odorless.
• Water is transparent in the visible part of the
electromagnetic spectrum.
• Water can act as either an acid or a base.
• Water is a universal solvent, dissolving many
substances found in nature.
4. Structure of Water
• Closely observe the structure of a water
molecule
• 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.
5. Conti…
• 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.
6.
7. Physical Properties of Water
• Water has some very important uses in our
world. It is the universal liquid and will find a
use in 99% of life’s functions. This unique
ability of water to be so versatile and due to
some of its very impressive properties. These
properties of water are often overlooked, but
are the main reason for what makes water
such a valuable compound.
8. Physical Properties of Water
• 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.
• Appearance: Water is colorless, odorless and tasteless
liquid in its natural state.
• Boiling Point: The boiling point is defined as the
temperature at which the vapour pressure of the liquid is
equal to the pressure surrounding the liquid, and thus the
liquid changes to vapor. water has a boiling point of 100 C.
This is because the hydrogen bonds in the water molecule
are very strong, They require a huge amount of energy to
break and start boiling.
9. Physical Properties of Water
• Freezing Point: The freezing point is the temperature at
which the substance changes state from liquid to solid. The
freezing point of water is 0 C. The fact that water is very slow
to freeze (or even boil for that matter) is very important for
our ecosystem and our survival.
• 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.
10. Chemical Properties of Water
• Amphoteric Nature:
One of the unique qualities of Water is its amphoteric
nature. An amphoteric substance is one which can act as
an acid or a base. While Water is neither acidic or basic it
acts as both. This is because of its ability to both donate
and accept protons. For acids stronger than water it acts
as a base. And it acts like a acid to bases stronger than
itself. These two following reactions show this
amphoteric nature.
–H2O (l) + HCl (aq) ⇌ H3O++ Cl–
–H2O (l) + NH3 (aq) ⇌ NH4+ + OH–
11. Chemical Properties of Water
• Hydrolysis Reaction:
• Because of its dielectric constant, water has a
very strong hydrating tendency. It dissolves a
wide range of ionic compounds. Water can
hydrolyze some covalent and ionic compounds.
• Redox Reactions:
• Water is a great source to obtain dihydrogen
since it can be reduced by reacting it with highly
electropositive metals such as Sodium.
– H2O + Na → 2NaOH + H2
12. The Phases of Water
• Solid Phase (Ice)
• The solid phase of water is known as ice and
commonly takes the structure of hard,
amalgamated crystals, such as ice cubes, or of
loosely accumulated granular crystals, such as
snow. Unlike most other substances, water’s solid
form (ice) is less dense than its liquid form, as a
result of the nature of its hexagonal packing
within its crystalline structure. This lattice
contains more space than when the molecules
are in the liquid state.
14. Liquid Phase (Water)
• Liquid Phase (Water)
• Water is primarily a liquid under standard conditions
(25 degrees Celsius and 1 atm of pressure). Water
forms a liquid instead of a gas because oxygen is more
electronegative than the surrounding elements, with
the exception of fluorine. Oxygen attracts electrons
much more strongly than does hydrogen, resulting in a
partial positive charge on the hydrogen atoms and a
partial negative charge on the oxygen atom. The
presence of such a charge on each of these atoms gives
a water molecule a net dipole moment.
15. Gas Phase (Water Vapor)
• The gaseous phase of water is known as water
vapor (or steam) and is characterized by a
transparent cloud. Water also exists in a rare
fourth state called supercritical fluid, which
occurs only in extremely uninhabitable
conditions. When water achieves a specific
critical temperature and a specific critical
pressure (647 K and 22.064 MPa), the liquid and
gas phases merge into one homogeneous fluid
phase that shares properties of both gas and
liquid.
16. The Polarity of Water
• The polar nature of water is a particularly important feature
that contributes to the uniqueness of this substance.
• The water molecule forms an angle with an oxygen atom at
the vertex and hydrogen atoms at the tips. Because oxygen
has a higher electronegativity than hydrogen, the side of the
molecule with the oxygen atom has a partial negative charge.
• An object with such a charge difference is called a dipole
(meaning “two poles”). The oxygen end is partially negative,
and the hydrogen end is partially positive; because of this, the
direction of the dipole moment points from the oxygen
toward the center position between the two hydrogen.
