Transcript General Chemistry • Element – composed of atoms • Nucleus – protons and neutrons • electrons.

General Chemistry
• Element
– composed of atoms
• Nucleus
– protons and neutrons
• electrons
General Chemistry
• Molecule
– a group of atoms held together by chemical
bonds
General Chemistry
• Bonds
– covalent bonds form when electrons are shared
General Chemistry
• Bonds
– ionic bonds form by attraction between
particles with opposite charges
Water
• H2O
• covalent bonds hold the 2 hydrogen & 1
oxygen together
Water
• Water molecules have an uneven
distribution of charge = polar
– H positive
– O negative
Water
• Polar nature of water leads to:
– attraction of other water molecules
– attraction of other charged or polar molecules
Water
• Hydrogen Bonds
– form between hydrogen of one water molecule
and the oxygen of another
– cohesion
Water spider
cohesion
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3 “states” of Water
•
•
•
•
Solid
Liquid
Gas
(and it can go back and forth between these
“states” many times!)
So you can have more than 1 state at a time…and why ice floats!
Water
• Universal solvent
• Solution
– solvent
– solute
Seawater
• 96.5% water & 3.5% solutes
• solutes change properties of water
Seawater
• 96.5% water and 3.5% solutes
• The SOLUTES are: 85% Salt (Sodium
Chloride) and 15% “other.”
Seawater
• Salinity
– total concentration of all dissolved inorganic
solids
– average = 3.5% or 35 ppt (35o/oo)
Seawater
• Source of ocean’s salts
– weathering of surface rocks
• sodium, magnesium, calcium
– outgassing
• chlorine, carbon dioxide, sulfur, hydrogen
Water is recycled continually
between the ocean and the land
• The reservoirs of water include:
– Oceans:
• cover 60% of the northern hemisphere
• cover 80% of the southern hemisphere
• contain 97% of Earth’s water
– Rivers, lakes and glaciers
– Groundwater
• contains a larger volume of water than all of the combined water in
lakes and rivers
• The hydrologic cycle describes the exchange of
water between ocean, land and atmosphere.
– On land precipitation exceeds evaporation.
– In the ocean evaporation exceeds precipitation.
Recycling of Water
Heat vs Temperature
• Heat
– energy produced by the random vibration of
atoms or molecules
• Temperature
– an objects response to the input or removal of
heat energy
Heat Capacity
• the heat required to raise the temperature of
1 gram of a substance by 1oC
• Heat capacity of water = 1 calorie
– the highest of all known substances
• water resists changing temperature when
heat is added or removed
Density and Temperature
• density of water increases as water is cooled
until a maximum of 1 g/cm3 is reached at
4 oC
• the density decreases as freezing takes place
• ice is less dense than water
Seawater vs. Pure Water
• Seawater has a
– lower heat capacity
– lower freezing point
• density increases until freezing point is
reached
– ice is pure water & cold, salty water left behind
sinks
Density of Water
• Depends on temperature and salinity
• density increases as temperature decreases
• density increases as salinity increases
Density Zones in the Ocean
• 1. surface zone or mixed layer
– temperature and salinity are constant with depth
• 2. a middle layer where density changes rapidly
with depth (because of extreme env. changes) =
pycnocline
– Thermocline: temp. changes rapidly w/ depth
– Halocline: salinity changes rapidly w/ depth
– NOTE: These 3 zones can ALL coincide together!
3. The DEEP ZONE (80% of all ocean water) is the
layer below the pycnocline (but little change occurs
here).
Fig 6-19, p.136
The Surface Layer
• About 100m thick
• Comprises about 2% of the ocean volume
• Is the most variable part of the ocean because it is
in contact with the atmosphere.
• Is less dense than the layers below because of its
lower salinity or higher temperature.
Sea Surface Temperatures
• Insolation and ocean-surface water temperature vary with the season.
• Ocean temperature is highest in the tropics (25oC) and decreases poleward.
The Pycnocline
• Is transitional between the surface and deep layers.
• Comprises 18% of the ocean basin.
• In the low latitudes, the pycnocline coincides with
the thermocline.
• In the mid-latitudes it coincides with the halocline.
• Tropical and subtropical oceans are permanently
layered with warm, less dense surface water
separated from cold, dense deep water by a
thermocline.
– The thermocline is a layer in which water temperature
and density change rapidly.
• Temperate regions have a seasonal thermocline
and polar regions have none.
The Deep Layer
• Represents 80% of the ocean volume.
• Water in the deep layer originates at the surface
in high latitudes, where it:
–
–
–
–
cools
becomes dense
sinks to the sea floor
flows equatorward across the ocean basin
Density Zones in the Ocean
• 3. the deep zone
– a cold (1 to 3oC), dense layer on the bottom
– most of the ocean (80%)
• The water column in the ocean can be divided into the:
– surface layer
– pycnocline
– deep layer
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Contrasting features of shallow and deep ocean water
Thermocline, Halocline, and
Pycnocline
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Refraction, Light and Sound
• Refraction: The “bending” of waves. Light
and Sound are a direct result/reaction of
these waves.
• Light and Sound waves travel at
DIFFERENT speeds depending upon the
medium that they are in.
Light in the Ocean
• Sunlight does NOT penetrate (always) to
the “bottom.” This is because of many
factors such as turbidity (sediments in the
water), depth and the scattering/absorption
of light through a water medium.
• Scattering determines how light is absorbed.
• Water thus absorbs (and scatters) the light
• PHOTIC vs. APHOTIC zones
Slide 52
“regular” ocean light penetration – blue dominates
Slide 53
strobe light penetration – blue HUES (+ other colors)
dominate
Slide 54
SOUND
• Similar to light – sound “waves” travel
differently through water.
• Speed of sound in average seawater (w/
average salinity) is 1500 m/sec.
sofar layer, in which sound waves travel at minimum speed
A side-scan sonar
image of the SS
Nailsea Meadow
resting on the
seabed at a depth
of 113 meters
(367 feet).
What does this mean to MARINE
LIFE?
• Light effects WHERE plants and animals
can live.
• Temperature effects WHERE plants and
animals can live.
• Salinity effects WHERE plants and animals
can live.
• Dissolved gases are an important factor too.
• In turbid coastal waters
light rarely penetrates
deeper than 20m.
– The water appears
yellow to green because
particles reflect these
wavelengths.
Fnft: Yangtze River