Transcript Properties of Water

Water is a Polar Molecule
• In some molecules atoms do not share electrons equally
What is the
net charge of
a water
molecule?
A: ZERO!
• The oxygen atom pulls on the shared electrons in each
hydrogen causing a partial POSITIVE charge on each
hydrogen and a partial NEGATIVE charge on the oxygen
Hydrogen Bonds
• Weak interactions between H with partial
positive charge and atoms with partial negative
charge
+
+
H
H
+
-O
H
+
••••••••• H
H-bond
O
-
• Form and break easily
• H-bonding allows water molecules to bind to
other polar molecules.
Unique Properties of Water
1. Cohesion and Adhesion
a. Surface tension
b. Capillary action
2. Excellent solvent
3. Temperature-stabilizing effects
Properties of Water
Honors Biology
Bhattacharya / Hammer
Capillary Action
• What will happen when straw is lowered into
water?
Capillary Action in Organisms
• Capillary action
allows roots to
absorb H2O from
soil
H2O
• Transpiration
(evaporation from
leaves) pulls H2O
upwards from roots
H2O
Solubility: Key Definitions
• Hydrophilic substance (water-loving)
– A polar molecule (e.g. glucose) that easily
dissolves in water
• Hydrophobic substance (water-dreading)
– A nonpolar molecule (e.g. oil) that resists
dissolving in water
H2O: Excellent Solvent
• H2O dissolves more substances than any other
known solvent
• H2O dissolves many types of salts and sugars,
many proteins, and a variety of hormones that
dissolve in blood and regulate various life
processes
• Small nonpolar molecules also dissolve
– Enough O2 dissolves to allow fish and other aquatic
life to survive
Temperature Stabilization
Properties of Water
• High specific heat
– H2O acts as a heat reservoir and its temperature remains
relatively stable
– Helps reduce temperature fluctuation in plants and animals
• High heat of vaporization
– It takes a lot of heat to evaporate just a little H2O
– This keeps water in lakes and ponds in the summer
• High heat of fusion
– It takes much longer for lakes and streams to freeze in winter
Temperature Stabilization
• Evaporative cooling
– During evaporation (liquid  gas), surface
temperature of water decreases
– Mammals sweat to stay cool in high temps
• H2O expands upon freezing
– When water freezes, each H2O molecule forms Hbonds with 4 other H2O molecules.
– Ice floats because this crystal structure is less dense
than liquid water.
– Lakes and ponds freeze over in the winter without
freezing all the living things in the water below.
Why is Ice Less Dense?
Why is Ice Less Dense?
Implications
Life goes on
below!