Properties of Water
Water and Ocean Structure
The Water Molecule
• H2O = 1 oxygen atom
and 2 hydrogen atoms
• Atoms are linked by
covalent bonds
• Polar molecule with
hydrogen atom positively
charged; oxygen atom
negatively charged.
• This polarity causes an attraction between neighboring
molecules
Dissolving Property of Water
• Water’s dissolving ability related to molecular structure
• Water separates compounds held together by opposite
electrical charges, i.e. salt (Na+ + Cl-)
• Positive hydrogen ion attracts negative chlorine ions; negative
oxygen ion attracts positive sodium ion
States of Water
• Water is only substance that naturally occurs in all 3 states
• Heat is a measure of how many molecules are vibrating and how fast
• Temperature is a measure of how rapidly the molecules are vibrating
• Thus, addition or loss of heat changes water’s physical property
Latent Heat
• Latent Heat of Fusion
– Amount of heat needed to
change from a solid to a liquid
• Latent Heat of Vaporization
– Amount of heat needed to
change from a liquid to a vapor
Latent Heat
• Water - freezes 0°C; boils 100°C
• Latent heat of vaporization (evaporation) is far greater than
latent heat of fusion (melting).
• All of the H bonds between H20 molecules must be broken to form
vapor
Heat Capacity of Water
• Ability of a substance to
change temperature with a
given amount of heat
• Water has a very high heat
capacity compared to land
• High heat capacity causes
slow temperature changes in
world’s ocean
• Helps keep the Earth’s surface
temperature stable
Heat Capacity for Common Substances
Heat Capacity of Water
Viscosity of Water
• The resistance of fluid to
flow
• Water has low viscosity
Exxon Valdez 1989
• Affected by temperature
• Surface water at equator is
warmer and less viscous
than Arctic
Surface Tension of Water
• Lateral and downward attraction between
individual molecules
• Creates a strong boundary at surface
• ↑ salt = ↑ surface tension
• ↓ H2O temp = ↑ surface tension
Water strider
Unique Property of Water
Why does ice float on water?
• When liquid H20 loses heat and
temperature lowers to freezing
point, ice forms
• Water expands as it freezes
– Angle between H and O atoms
in H20 molecule increases from
105° to 109°
• Ice less dense than water
– ice floats
Density of Water
Density of water is affected by:
• Temperature
– As water first cools, density
increases and volume decreases
– Below 4°C, density decreases
– At 0°C, ice forms, density
decreases rapidly
• Salinity
– Adding salts increases density
– Fresh H20 floats on salt H20
Density of Water
Compressibility of Water
• Substance’s ability to
undergo volume
changes
• Water has slight
compressibility
• # of molecules/unit
volume does not
change much
Transmission of Light
Why is the ocean blue?
• Photic zone – maximum
light penetration
• Intensity of light decreases
with depth
• 65% of light absorbed in 1st m
– Only 1% reaches 100 m
• No visible light below 1,000 m
– Water absorbs red, orange,
yellow and ultraviolet
wavelengths
– Only blue light remains where it
is reflected and scattered
Transmission of Light
• Refraction
– As light passes from less dense air
to more dense water, it changes
speed and bends
– Light travels faster through water
than air
Transmission of Sound
• Sound travels faster in water
• Sound velocity in water =
1,500 m/sec (5x greater than
in air)
• Sound speed increases with
pressure, temperature and
salinity
• Use sound with sonar
Sound and Locating Objects
• When sound speed decreases with depth, waves are bent downward
• When sound speed increases with depth, waves are bent upward
• An area exists where no sound waves travel – shadow zone