Water

Properties of Water Polar molecule Cohesion and adhesion High specific heat Density – greatest at 4oC

Polarity of Water In a water molecule two hydrogen atoms form single polar covalent bonds with an oxygen atom. (Gives water more structure than other liquids) Oxygen has a partial negative charge. Hydrogen atoms have a partial positive charge. A water molecule is a polar molecule with opposite ends of the molecule with opposite charges.

Interaction Between Water Molecules Negative Oxygen end of one water molecule is attracted to the Positive Hydrogen end of another water molecule to form a HYDROGEN BOND

Hydrogen Bonds Exist Between Water Molecules Formed between a highly Electronegative atom of a polar molecule and a Hydrogen One hydrogen bond is weak , but many hydrogen bonds are strong Each water molecule can form hydrogen bonds with up to four neighbors.

Bonds to 4 molecules directly

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Hydrogen Bonds Hold water molecules together Extraordinary Properties that are a result of hydrogen bonds: Cohesive behavior Resists changes in temperature High heat of vaporization (specific heat) Expands when it freezes

Cohesion Attraction between particles of the same substance ( why water is attracted to itself) Results in Surface tension (a measure of the strength of water’s surface) Produces a surface film on water that allows insects to walk on the surface of water 1

Surface tension, a measure of the force necessary to stretch or break the surface of a liquid, is related to cohesion. Water has a greater surface tension than most other liquids because hydrogen bonds among surface water molecules resist stretching or breaking the surface. Some animals can stand, walk, or run on water without breaking the surface. Fig. 3.3 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Cohesion = Surface Tension Helps insects walk across water

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Adhesion Attraction between two different substances. Water will make hydrogen bonds with other surfaces such as glass, soil, plant tissues, and cotton. Capillary action -water molecules will “tow” each other along when in a thin glass tube. 1

Capillary action occurs when the forces binding a liquid together (cohesion and surface tension) and the forces attracting that bound liquid to another surface (adhesion) are greater than the force of gravity.                                                                                                                                                                                                                                                                                  droplets.

Adhesion Causes Capillary Action Which gives water the ability to “climb” structures

Plants rely on capillary action Cohesion among water molecules plays a key role in the transport of water against gravity in plants Adhesion, clinging of one substance to another, contributes too, as water adheres to the wall of the vessels.

Capillary Action = cohesion + adhesion

Adhesion Also Causes Water to … Attach to a silken spider web Form spheres & hold onto plant leaves

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Homeostasis Ability to maintain a steady state despite changing conditions Water is important to this process because: a. Makes a good insulator b. Resists temperature change c Coolant d. Ice protects against temperature extremes (insulates frozen lakes) 4

Specific Heat is the amount of heat that must be absorbed or lost for one gram of a substance to change its temperature by 1oC. 3/4 of the earth is covered by water. The water serves as a large heat sink responsible for: Prevention of temperature fluctuations that are outside the range suitable for life. Coastal areas having a mild climate A stable marine environment

Insulates the Earth Water vapor forms a kind of global ‘‘blanket” which helps to keep the Earth warm. Heat radiated from the sun warmed surface of the earth is absorbed and held by the vapor. 1

Evaporative Cooling The cooling of a surface occurs when the liquid evaporates This is responsible for: Moderating earth’s climate (as mentioned before) Stabilizes temperature in aquatic ecosystems Preventing organisms from overheating

Density of Water The density of water: Prevents water from freezing from the bottom up. Ice forms on the surface first —the freezing of the water releases heat to the water below creating insulation. Makes transition between seasons less abrupt.

Ice is about 10% less dense than water at 4oC. When water reaches 0oC, water becomes locked into a crystalline lattice with each molecule bonded to the maximum of four partners. As ice starts to melt, some of the hydrogen bonds break and some water molecules can slip closer together than they can while in the ice state. Ice is about 10% less dense than water at 4oC. Fig. 3.5 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Water is Less Dense as a Solid Which is ice and which is water? 1

Water is Less Dense as a Solid Ice 1

30 Second Concept Check!

Let’s recap… Your answer to each of the following will be either: Polarity Cohesion Adhesion Specific Heat Density Hold up either 1, 2, 3, 4 or 5 to show your response

Water molecules creating a hydrogen bond with each other! Polarity Cohesion Adhesion Specific Heat Density Water molecules creating a hydrogen bond with each other!

Temperature of water rises and falls very slowly Polarity Cohesion Adhesion Specific Heat Density Temperature of water rises and falls very slowly

Hydrogen molecule is slightly positive Polarity Cohesion Adhesion Specific Heat Density Hydrogen molecule is slightly positive

Capillary action is brought on by this! Polarity Cohesion Adhesion Specific Heat Density Capillary action is brought on by this!

Leads to surface tension of water Polarity Cohesion Adhesion Specific Heat Density Leads to surface tension of water

Water freezes from the surface on down Polarity Cohesion Adhesion Specific Heat Density Water freezes from the surface on down

Oxygen molecule is slightly negative Polarity Cohesion Adhesion Specific Heat Density Oxygen molecule is slightly negative

Plants rely on these TWO properties of water to transport water within Polarity Cohesion Adhesion Specific Heat Density Plants rely on these TWO properties of water to transport water within

Bugs can walk on water due to this property! Polarity Cohesion Adhesion Specific Heat Density Bugs can walk on water due to this property!

This property allows our bodies to maintain homeostasis Polarity Cohesion Adhesion Specific Heat Density This property allows our bodies to maintain homeostasis

This property was evident when trying to float the needle on water Polarity Cohesion Adhesion Specific Heat Density This property was evident when trying to float the needle on water

This property was evident when dropping water onto a penny Polarity Cohesion Adhesion Specific Heat Density This property was evident when dropping water onto a penny

This property was evident when using the tube to “draw” up water Polarity Cohesion Adhesion Specific Heat Density This property was evident when using the tube to “draw” up water

Polarity Cohesion Adhesion Specific Heat Density This property was evident when freezing the water to see if it froze top/bottom first.

Polarity Cohesion Adhesion Specific Heat Density This property was evident when freezing the water to see if it froze top/bottom first.

These TWO properties were evident when transporting water on a string! Polarity Cohesion Adhesion Specific Heat Density These TWO properties were evident when transporting water on a string!

Polarity Cohesion Adhesion Specific Heat Density This property was evident when dropping substances onto pepper in water

This property was evident when heating water versus oil. Polarity Cohesion Adhesion Specific Heat Density This property was evident when heating water versus oil.

How did you do?? Hold your cards up and rate yourself a 1-5… 1 = I didn’t learn anything … boo!  5 = I can repeat all of this information back to you already! Bam!