Download The Hydrosphere - RRMS 8th Grade Science

Unit 4: The Hydrosphere
Part 1: Structure of the
Hydrosphere
Part 2: Oceans
Part 3: Water Quality
Part 1: The Structure of the
Hydrosphere
Objectives:
1.Characteristics of Water
2.The Water Cycle
3.Reservoirs within the Hydrosphere
4.River Basins
Properties of Water
• Water has unique properties that impact
the role it plays on the Earth.
o Polarity
o Cohesion
o Adhesion
o High surface tension
o Density
o High specific heat
o High heat of vaporization
The Water Molecule
• Made of 2 H atoms and 1 O atom
• The atoms share valence electrons to form
covalent bonds.
Water is Polar Covalent
• However, the electrons are not shared equally.
• Oxygen has a much stronger attraction for the
electrons so the shared electrons get pulled closer
to the oxygen.
• This makes the oxygen slightly negative and the
hydrogen atoms slightly positive.
• This unequal sharing of electrons is called
polarity.
Water is Polar Covalent
Partially
negative
Partially
positive
Most of the properties of water are
due to polarity!
Cohesion
• Attraction of water molecules to each
other.
Surface Tension
• Cohesion cause surface tension. Molecules on the
surface have no neighbors above so they pull more
strongly on those beside and below them.
– This forms a surface "film" which makes it more difficult to
move an object through the surface than to move it when it is
underwater.
– This also makes water form drops because the surface
molecules are pulled inward.
Surface Tension
• Water attracts itself and pulls in to form a
drop with a “film” on its surface.
Adhesion
• Attraction of water to an unlike substance
Cohesion and Adhesion
What forms a drop?
• Cohesion causes water to form drops
• surface tension causes them to be nearly
spherical
• adhesion keeps the drops in place.
Interesting Polarity Facts
• Polar substances stick to other polar
substances.
–Polar ↔ Polar = High Adhesion
–Polar ↔ Nonpolar = Low Adhesion
Water Drop Shapes
• Water coheres to itself and
forms a nice, round drop.
• On a nonpolar surface the
drop stays round (low
adhesion)
• On a polar surface the drop
flattens out because polar
water “sticks” to the polar
surface. (higher adhesion)
Capillary Action– water moves through
narrow, porous spaces
• Some of the
molecules adhere to
the surface of the
object.
• The other molecules
that are cohered to
them are pulled
along.
Adhesion to surface of object
Cohesion of water to water
Capillary action of
absorbent paper
Interesting Polarity Facts
• “Like dissolves like”
• Polar solvents dissolve polar substances.
• Nonpolar solvents dissolve nonpolar substances
• BUT Polar and Nonpolar don’t mix.
• Water is called the universal solvent because so
many things will dissolve in it.
“Like Dissolves Like”
• Oil and water do not mix.
Oil is nonpolar
Water is polar
Density of Water
• Cold water is more dense than water up to the
freezing point.
• So cold water sinks and warm water rises.
• This happens in the oceans and regulates our
climate.
Density of Water
• Solids are usually more dense than liquids.
• Solid water (ice) is actually less dense then
liquid water.
• That means ice floats on water.
– Important for lakes/ponds
High Specific Heat of Water
• Specific Heat (or heat capacity) is the amount
of heat (i.e. thermal energy) needed to raise
the temperature of a substance.
• High Specific Heat = lots of heat to raise the
temperature = takes longer
• Low Specific Heat = little heat needed to raise
the temperature = quicker
High Specific Heat of Water
• This means water can absorb a lot of heat
without changing temperatures drastically.
• Large bodies of water maintain a moderate
temperature even when the air temperature
changes drastically.
High Heat of Vaporization
• Heat of Vaporization: amount of heat needed
to vaporize a liquid
• This makes evaporation a cooling process.
• Water has a high heat of vaporization which
means that when water evaporates it takes a
lot of heat with it.
Water, Water Everywhere!
• Water is one of the most common
substances on the surface of the Earth.
• Water covers about 71% of the planet
– Exists as a solid (ice), liquid (water), or gas
(vapor)
• But less than 1% is drinkable
Distribution of Water on Earth
All Water
Fresh Water
Easily Accessible
Fresh Water
The Water Cycle
• The total amount of water on Earth is
constant.
• But the water can move to different reservoirs
and change phases.
– A reservoir is a storage location for water (the
atmosphere, oceans, lakes, glaciers, etc.)
– Residence time is the amount of time that water
stays in a given reservoir.
• Energy from the sun drives the water cycle
The Water Cycle
infiltration
Water Cycle
• Go to
http://www.hippocampus.org/Earth%20Science
• Click on Environmental Science
• Then choose Water Cycle
Hydrosphere Reservoirs: Atmosphere
• Contains water vapor
• Average residence time = 10 days
Hydrosphere Reservoirs: Ice
• Frozen water is found in the polar ice caps,
glaciers, and icebergs.
• The oldest ice sample identified had an
estimated residence time of 900,000 years
Hydrosphere Reservoirs: Groundwater
• Water that moves through the soil through
the process of infiltration.
Infiltration
Water Table
Saturated Zone (Permeable Layer)
Impermeable Layer
Hydrosphere Reservoirs: Groundwater
An aquifer is an underground layer of waterbearing permeable rock or unconsolidated
materials (gravel, sand, or silt) from which
groundwater can be extracted using a well.
Hydrosphere Reservoirs: Groundwater
• Potential Threats to Groundwater
– Overuse and depletion
– Contamination
– Improper wastewater management
– Pharmaceutical and personal care products
– Nitrates
Hydrosphere Reservoirs: Groundwater
Hard vs. Soft Water
• Hard water contains dissolved minerals (like
calcium and magnesium)
– Tastes good, BUT it can be damaging to plumbing and
soaps don’t lather well.
• Soft water contains almost no dissolved minerals
(except sodium).
– If it is too soft, then it doesn’t taste as good, but it is
easier on the plumbing and works better for washing.
Hydrosphere Reservoirs: Lakes
• Large bodies of surface water found on
continents.
Hydrosphere Reservoirs: Rivers & Streams
• Account for a very small % of water, but are
very important!
• Carry water out to the ocean
Hydrosphere Reservoirs: Wetlands
• Areas of land that are covered with a shallow
layer of water for at least part of the year
• Marshes-grassy wetlands
• Swamps-wetlands that have trees and bushes
• Importance:
– Recharge groundwater
– Filter water
– Habitat for many birds and animals
Hydrosphere Reservoirs: Estuaries
• The point where a river meets the ocean.
• Contain a mix of fresh and salt water called
brackish water.
• Aquatic nurseries
Hydrosphere Reservoirs: Oceans
• Salty because water (the universal solvent)
dissolves chemicals from the soil and deposits
them in the oceans.
• Volcanoes release solid and gaseous materials
that contribute.
• And hydrothermal vents on the ocean floor
release superheated ocean water from the
earth.
Hydrosphere Reservoirs: Oceans
• Oceans are critical to maintaining our climate
• Oceans collect, mix, and circulate water, heat
and carbon dioxide.
– High Specific Heat, High Heat of Vaporization, and
the unique density of water are critical in
maintaining moderate temperatures on the Earth.
Average Residence Times
River Basins
• River basins include the entire land surface
drained by the various streams and creeks
that flow downhill into one another, and
eventually into one river.
• The final destination of the water drained by a
river basin is an estuary or an ocean.
– A river basin sends all the water falling on the
surrounding land into a central river and out to
the sea.
River Basins
• Everyone lives in river basin.
• Our actions will affect water quality far from
our homes because the water will travel
across the land, into a river, and out to the
ocean.
• Topography determines the river basin.
– Water flows downhill!