Download Water Cycle

Chapter 3
Section 3.1
The Hydrological Cycle
(The Water Cycle)
Properties of Water
• All living things need water to survive.
• Water is the universal solvent which most
reactions take place in.
• Understanding the properties of water can
help in understanding the water cycle.
• Water molecules (H20) are made up of 1 oxygen
atom and 2 hydrogen atoms.
• Water molecules are held together by covalent
bonds.
• A covalent bond refers to the sharing of
electrons between the atoms.
• Although they share the electrons, they do not
share them evenly.
• Oxygen is more electronegative than hydrogen,
so therefore the oxygen will pull more strongly
on the electrons.
• Since electrons are negatively charged,
and the oxygen molecules are pulling the
electrons more strongly toward them, the
oxygen atom will have a partially negative
charge and the hydrogen atoms will have a
partially positive charge.
• This type of molecule, with a difference in
charge from one end to the other, is
referred to as a polar molecule.
Water As A Polar Molecule
Hydrogen Bonds
• When there are many water molecules in close
proximity they have a tendency to stick together.
• This is because the negative end of one water
molecule attracts the positive end of another
water molecule.
• This attraction forms a weak bond known as a
hydrogen bond.
Hydrogen Bonds
Negative oxygen end is attracted
to the positive hydrogen end on the
next molecule = hydrogen bond.
Water is Wierd
• http://ed.ted.com/lessons/how-polaritymakes-water-behave-strangely-christinakleinberg
The Hydrological Cycle
• The movement of water through the biosphere
from the atmosphere to Earth and back is called
the hydrological cycle or the water cycle.
• Water moves from the Earth to the atmosphere
by the following processes:
- Evaporation: water changing from a liquid to
water vapour
- Transpiration: the loss of water through plant
leaves
Transpiration
• Once water is in the atmosphere it
undergoes condensation and forms tiny
droplets of liquid water that remain
suspended in the atmosphere as clouds.
• Condensation is the process of changing
from a gas to a liquid.
• The clouds form precipitation (rain, snow,
sleet, hail) and when the time is right the
liquid drops come together and once they
are too heavy to remain in the cloud they
fall to the Earth.
Got Rain?
Lets draw it again…
Water Beneath the Soil
• The fresh water that we use comes from
two sources: ground water and surface
water.
• Precipitation that collects above the
ground in lakes, pond, rivers and oceans
is called surface water.
• Precipitation increases surface runoff from
the rivers and lakes to the ocean.
• The water on the surface filters downwards
because of gravity, this downward pull is called
percolation.
• As water seeps downwards, it carries dissolved
organic matter and minerals to the bottom layers
of soil, this process is called leaching.
• Eventually, water will saturate the lower levels of
soil, making the water table.
Acid Deposition and The Water
Cycle
• Our technologies such as factories and cars
produce sulphur dioxide and nitric oxide, the
most dangerous of the air pollutants.
• The sulphur dioxide and nitric oxide enter the
atmosphere and combine with water droplets to
form acids.
• The acids return to the surface of Earth in the
form of snow or rain, called “acid rain.”
The Effects of Acid
•
Acid rain can have many effects on our ecosystems,
such as:
- killing fish
- killing soil bacteria
- killing aquatic and terrestrial plants
- leaching nutrients from the soil
•
However, the oxides do not always enter the water
cycle.
Depending on weather conditions the particles can
remain in the air and settle in their dry state.
This is known as dry acid deposition.
These pollutants then form acids when they combine
with surface water.
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