CHAPTER 6
Water and Seawater
H2O molecule
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Two hydrogen H and one oxygen O
atoms bonded by sharing electrons
Both H atoms on same side of O atom
Dipolar
Hydrogen bonding
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Fig. 5.3
Polarity means small
negative charge at
O end
Small positive
charge at H end
Attraction between
+ and – ends of
water molecules to
each other or other
ions
Hydrogen bonding

Hydrogen bonds are weaker than
covalent bonds but still strong enough
to result in
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High surface tension
High solubility of chemical compounds in
water
Solid, liquid, gas at Earth’s surface
Unusual thermal properties
Unusual density
Water molecules in different
states of matter
Fig. 5.5
Surface Tension
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A measure of the tendency of surface
molecules of liquid to cling together
Evidence of hydrogen bonding
Cohesion – strong attraction between
water molecules
Adhesion – water clings to many
surfaces

Capillarity (ex. This is how plants transport
water from roots to stems.)
Viscosity
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A measure of the tendency of a
substance to resist flow.
Increased by hydrogen bonding
in H2O
Increases in water with
decreasing temperature,
increasing salinity, and
decreasing pressure
Light Transmission
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Underwater true colors can only be seen
near the surface
As depth increases more of the red end
of the spectrum is absorbed and blue is
reflected
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Top 10 m red wavelengths are absorbed
Within 100 m yellow is absorbed
Blue and green to about 250 m (w/ fewer
green as depth increases)
No light beyond 1000 m
Light Transmission, cont…

Particles suspended in water column
 Mud and sediment
 Plankton and photosynthesis
 More particles the less light is
transmitted
 Secchi disk – measures visible light
transmission

Turbidity is the amount of suspended matter,
is greater at shallow depths.
Sound Transmission
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Travels more efficiently through water
than air
Velocity increases as temperature,
salinity, and pressure increase
SOFAR (Sound Fixing And Ranging)
channel

Marine mammals may use for long-distance
communication
Changes of state due to adding or
subtracting heat
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Heat is energy of moving molecules
Temperature is measurement of
average kinetic energy
Calorie is amount of heat needed to
raise the temperature of 1 gram of
water by 1o C
Unusual thermal properties of H2O
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High boiling point (100°C)
High freezing point (0°C)
Most H2O is in the form of water
(liquid) on Earth’s surface (good for
life)
High latent (hidden) heats of
 Vaporization/condensation
 Melting/freezing
 Evaporation
Fig. 5.6
Unusual thermal properties of H2O

Water high heat capacity
Amount of heat required to raise the
temperature of 1 gram of any
substance 1oC (1 calorie/gram/°C)
 Water can take in/lose lots of heat
without changing temperature
 Rocks low heat capacity

 Rocks
quickly change temperature as
they gain/lose heat
Global thermostatic effects

Moderate temperature on Earth’s
surface
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Marine effect
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Equatorial oceans (hot) don’t boil
Polar oceans (cold) don’t freeze solid
Oceans moderate temperature changes
day/night; different seasons
Continental effect

Land areas have greater range of
temperatures day/night and during different
seasons
Density of water
Density of water increases as
temperature decreases
 Density of ice is less than density
of water
 From 4oC to 0oC density of water
decreases as temperature
decreases

Density of water
Fig. 5.10
The Hydrologic/Water Cycle
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Consists of reservoirs and fluxes
Reservoirs are locations where water is
found
Fluxes are the reactions or pathways
that takes water from one reservoir to
another
Closed cycle
Hydrologic cycle describes recycling
of water near Earth’s surface
Fig. 5.15
Residence time
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Average length of time a substance
remains dissolved in seawater
Ions with long residence time are in
high concentration in seawater
Ions with short residence time are in
low concentration in seawater
Steady state condition
Average reservoir residence times
Reservoir
Oceans
Average residence time
2000 years
Glaciers and land ice
10 to 1000 years
Seasonal snow cover
2 to 6 months
Soil moisture
1 to 2 months
Groundwater: shallow
Groundwater: deep
0.003 to 1000 years
10,000 years
Lakes
1-3 years
Rivers
0.03 years
Atmosphere
0.0307 years
Residence time and steady state
Fig. 5.16
The END!!!!