The Wonderful WorldThe Wonderful World of Water of Water

The importance of water

• Water covers 71% of Earth’s surface

But not all of that water is usable

• You are mostly made of water

In fact, water is crucial to life as we know it!

• Life on Earth originated in the oceans

This is why astronomers look for planets in the “goldilocks zone” where liquid water could exist

It is thought that Mars once had liquid water

• So life may have once existed there.

This simple molecule is involved in all aspects of our life.

• It shapes land through erosion and weathering

• It influences our climate (long term weather patterns)– Forms different types of air masses over land and sea,

reflects sunlight using clouds and glaciers, forms precipitation, ocean currents and temperature influence local climates

• Ancient civilizations settled near water and worshiped rain gods.

• Wars have been fought over access to water

http://en.wikipedia.org/wiki/Water_conflict

So what makes this simple molecule so amazing?

• Water has some unique properties

• A water molecule (H2O), is made up of three atoms --- one oxygen and two hydrogen. H

H

Water is PolarWater is Polar• In each water molecule, the

oxygen atom attracts more than its "fair share" of electrons

• The oxygen end has a negative charge

• The hydrogen end has a positive charge

• However, water is neutral (equal number of e- and p+) = Zero Net Charge

These charges allow water These charges allow water molecules to “stick” togethermolecules to “stick” together

The negative oxygen end of one water molecule is attracted to the positive hydrogen end of another water molecule to form a HYDROGEN BOND

© 2011 Pearson Education, Inc.

Animation: Water StructureRight-click slide/select “Play”

These hydrogen bonds allow for some interesting behavior by

water• Phases of Matter

• Heat Capacity

• Cohesion

• Adhesion

Phases of Matter

• Water exists in all three phases on Earth

• At sea level, pure water boils at 100 °C and freezes at 0 °C.

• Water vapor is made of water (H20) in gas form. The molecule is still made of three atoms.

Properties of WaterProperties of Water• The boiling The boiling

temperature of water temperature of water decreases at higher decreases at higher elevations (lower elevations (lower atmospheric pressure). atmospheric pressure).

• For this reason, an egg For this reason, an egg will take longer to boil will take longer to boil at higher altitudes (it at higher altitudes (it takes longer to cook takes longer to cook food at a lower food at a lower temperature)temperature)

Water is Less Dense as a SolidWater is Less Dense as a Solid

• Ice is less dense as a solid than as a liquid (ice

floats)

• Liquid water has hydrogen bonds that are

constantly being broken and reformed.

• Frozen water forms a crystal-like lattice

whereby molecules are set at fixed distances.

Water is Less Dense as Water is Less Dense as a Solida Solid

•Which is ice and which is Which is ice and which is

water?water?

Water is Less Dense as a Water is Less Dense as a SolidSolid

WaterWater IceIce

CohesionCohesion• Cohesion: an attraction between molecules of

the same kind.

• Hydrogen bonds allow one water molecule to stick to other water molecules

• This results in surface tension (a measure of the strength of water’s surface)

https://www.youtube.com/watch?v=ciqNNRlS2yA

Surface tension

Surface tension created by Surface tension created by cohesion…cohesion…

Helps animals remain on the surface of the water

http://www.youtube.com/watch?v=45yabrnryXk

AdhesionAdhesion• Adhesion is the attraction between two different

substances.• Water will form hydrogen bonds with other surfaces

such as glass, soil, plant tissues, and cotton.

Cohesion vs. Adhesion

• Cohesion- two alike substances attracted to one another

• Adhesion- two different substances attracted to one another

Adhesion allows plants to pull in water

• Capillary action - water molecules will “tow” each other along when in a thin glass tube or along a paper towel.

• The thinner the tube, the higher the water can “climb”

Capillary Action in a paper towel

• The water is adhering to the paper towel.

This calendar uses capillary action to absorb ink, one day at a time

Adhesion Causes Capillary Adhesion Causes Capillary ActionAction

• Transpiration is the water released from

plant leaves

• Transpiration: water vapor is released by plants.

© 2011 Pearson Education, Inc.

Animation: Water TransportRight-click slide/select “Play”

Adhesion

Two types ofwater-conducting

cells

Cohesion

300 m

Directionof watermovement

Water has high heat capacityWater has high heat capacity

• Water resists temperature change, both for heating and cooling.

• Water can absorb or release large amounts of heat energy with little change in actual temperature.

• Which takes longer to heat up? A pot with water or a pot with no water?

Heat Capacity of water influences the climate of areas near water

Figure 3.5

Santa Barbara 73°

Los Angeles(Airport) 75°

Pacific Ocean 68°

Santa Ana 84°

Burbank90°

San Bernardino100°

Palm Springs106°

Riverside 96°

San Diego 72° 40 miles

70s (°F)

80s

90s

100s

Why does Phoenix AZ have a greater temperature range

than San Diego CA?

Water, like all matter, cannot be created or destroyed

• The same water molecules you drink today have been around for billions of years!

• It originally arrived on earth from comets!

Measurements from the Herschel Space Observatory show that comet Hartley 2, which comes from the distant Kuiper Belt, contains water with the same chemical signature as water in Earth's oceans. The findings may help explain how Earth’s surface ended up covered in water.

Water is constantly recycled• The Water Cycle is the continuous process by

which water moves from Earth’s surface to the atmosphere and back.

• Driven by energy from the SUN.

2

3 3

Processes of the Water Cycle1. The Sun heats up the water in Earth’s oceans

and lakes.

Processes of the Water Cycle2. Evaporation: liquid water changes to a gas called water vapor.

Processes of the Water Cycle• Transpiration: water vapor is released by plants.

Processes of the Water Cycle3. Condensation:3. Condensation:•Warm air carries water Warm air carries water vapor upward.vapor upward.

•The air cools and condenses The air cools and condenses into liquid water.into liquid water.

•Tiny droplets of water Tiny droplets of water clump together around tiny clump together around tiny dust particles in the air, dust particles in the air, forming clouds. forming clouds.

Licancabur Volcano is located on the border between Chile and Bolivia.

Processes of the Water Cycle4. Precipitation:•As more water vapor condenses, the drops of water grow larger and heavier.

•The heavy droplets fall as precipitation (rain, snow, sleet, hail).

Processes of the Water Cycle5. The precipitation that falls on land may:

• soak into the soil and become groundwater

OR

•Run off the land, eventually flowing back into the ocean.

Water that falls on the surface may run off into rivers and streams, eventually flowing back to a lake or ocean.

Water Cycle Video