Understanding Water
STRUCTURE OF WATER MOLECULE
Hydrogen
atom
Hydrogen
atom
Formula:
H2O
Oxygen
atom
POLARITY OF WATER
• Different sides
of molecule
have different
charges.
• Due to unequal
sharing of
electrons.
H+
H+
O-
• Oxygen side is negative
because it has a
stronger attraction of
electrons.
COVALENT BONDING
Sharing electrons
• Sharing of
electrons
between atoms
• Oxygen has 6
valence electrons
• Hydrogen has 1
valence electron
H
H
O
Cohesion
• Water molecules stick
to each other.
– Positive side attracted
to negative side
• Creates surface
tension
• Water is pulled easily
through small vessels
(capillary action)
Adhesion
• Water
molecules
stick to other
substances.
• Water
molecules
can be pulled
through
other
substances.
Water molecules
attracted to
paper towel
Water molecules being
attracted to side of a
small glass tube. A
meniscus is the dip in
the water surface due
to this attraction.
Low density of ice
• Less dense than
water
– Ice = 0.9164 g/ml
– Water = 0.9999 g/ml
• Floats on water
• Lakes and ponds
freeze from top to
bottom
– Insulates ponds from
freezing solid
– Protects organisms in
ponds and lakes
Arrangement of ice provides s pace between
molecules so it is lighter than water.
High Heat of Vaporization
• It takes a lot of
energy for water to
evaporate.
• This prevents
excessive loss of
water from lakes and
ponds in summer.
High heat causing water
to evaporate.
High Specific Heat
• It takes a lot of energy to change
the temperature of water.
– Water has the highest specific heat
of all liquids except ammonia.
– Heat energy used to break
molecules is not available for
increased kinetic energy for
evaporation. It would take more
energy for evaporation.
– Larger numbers of water molecules
per gram allows it to absorb more
heat energy thus buffering against
heat loss
• This helps to maintain constant
temperature of oceans and body
temperature.
Substance
Specific Heat
(cal/g-C)
Water
1.00
Aluminum
0.215
Iron
0.108
Gold
0.031
Specific Heat for water:
It takes 1 calorie of energy to raise 1
gram of water I degree Celsius
Universal Solvent
• Ionic and polar substances dissolve best in water.
– Ionic and polar molecules have charges
– Water is attracted to parts of other molecules causing
them to separate. (see below)
– Minerals and nutrients can be dissolved and
transported more quickly and better throughout
organisms.
– Main solvent in organisms.
Acids and Bases
•
•
•
•
Acids have excess H+ ions.
Bases have excess OH- ions.
Neutral water has equal amounts of H+ and OH- ions.
pH measures the concentration of H+ ions.
pH scale
ACIDS
1
2
(Strongest)
3
NEUTRAL
4
5
6
(Weakest)
7
8
BASES
9
10
(Weakest)
11
12
13
14
(Strongest)