1. SC.912.L Properties of Water that contribute to Earth’s suitability as an environment for life: 1. Cohesive behavior. 2. Ability to moderate temperature. 3. Expansion upon freezing. 4. Versatility as a solvent

2. How does the structure of water contribute to its unique properties?
Because water is a polar molecule, it is able to form multiple hydrogen bonds, which account for many of water’s special properties.

3. Polarity and Hydrogen Bonding
Water is a polar molecule.
Polar molecules have slightly
charged regions. The molecule
is a bit like a magnet with two poles. O H _ +
Polar molecules—molecules that have regions with slight electrical charges due to uneven
pull on electrons
Nonpolar molecules—molecules without charged regions due to equal pull on electrons
1. hydrogen bonds
2. formed by attraction between slightly positive hydrogen atom and slightly negative
(oxygen) atom
Atom 1—oxygen; slightly negative
Atom 2—hydrogen; slightly positive
Nonpolar molecules do not have charged regions.
Hydrogen bonds is a weak bond formed between
slightly positive hydrogen atoms and slightly negative
atoms. 3

4. Structure of Water Polar Molecule Hydrogen Bonds
(electrons are unevenly distributed)

5. Cohesion
Cohesion is an attraction between molecules of the same substance. Because a single water molecule may be involved in as many as four hydrogen bonds at the same time, water is extremely cohesive

6. The hydrogen bonds that form when the negative end of a water molecule attracts the positive end of another water molecule causes water molecules “stick” to each other.
A water molecule attracts another water molecule, “stick” to each other, cling together.
Cohesion causes water molecules to be drawn together, which is why drops of water form beads on smooth surface.

7. Because of the cohesive properties of water, trees such as the giant sequoia are able to transport water molecules from the soil to their leaves 300 ft. above.
WATER: STRONG COHESIVENESS
300 ft.
Water molecule released into the atmosphere
As each water molecule evaporates, it pulls additional water up through the tree because of the “sticky-ness” of the hydrogen bonds that link the water molecules.
Water molecules pulled upward
6-ft.-tall man
What is Life? A Guide to Biology
2010 W.H. Freeman and Co
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Water molecule pulled into root system

8. Phloem and Xylem
Celery lab demo
Celery image:
Phloem and Xylem image:
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Demo celery
Xylem-System of tubes in a plant that transport water and dissolved minerals. The xylem distributes the water throughout the plant.
Phloem-Transport sugars and molecules created by the plant. Transports food made during photosynthesis.

9. The cohesive forces between liquid molecules are responsible for the phenomenon known as surface tension. The molecules at the surface do not have other like molecules on all sides of them and consequently they cohere more strongly to those directly associated with them on the surface. This forms a surface “film” or elastic “skin” Cohesion produces surface tension, explaining why some insects and spiders can walk on a pond’s surface.
Surface Tension

10. Because of cohesion, water and other liquids form thin films and drops, and flows upward against the force of gravity through the stem of a plant

11. Adhesion
Adhesion is an attraction between molecules of different substances. Water molecules are attracted to many other similarly polar substances. Adhesion powers a process, called capillary action, in which water molecules move upward through a narrow tube, such as the stem of a plant.

12. Ability to Moderate Temperatures
Because of the multiple hydrogen bonds between water molecules, it takes a large amount of heat energy to cause those molecules to move faster and raise the temperature of the water. Water has a high specific heat, which means that is hard for water to change temperature. Specific heat is the amount of energy needed to rise the temperature of 1 gram of a substance by 1 °C . The specific heat of water is 4.18 J/g x °C. Therefore, water takes a long time to heat up or to cool down. Water’s heat capacity, the amount of heat energy required to increase its temperature, is relatively high.

13. This property of water allows lake, stream, and ocean ecosystems to maintain stables temperatures, even if air temperatures change dramatically.
The high specific heat of water also helps your body maintain a constant internal environment.
Large bodies of water, such as oceans and lakes, can absorb large amounts of heat with only small changes in temperature. This protects organisms living within from drastic changes in temperature.
At the cellular level, water absorbs the heat produced by cell processes, regulating the temperature of the cell.

14. Water absorbs heat more slowly and retains this energy longer than many other substances do. This property of water allows organisms to maintain a stable internal environment. Bodies of water remove heat energy from the atmosphere during the day, and release stored heat at night. Water plays an important role regulating temperatures on Earth.

15. Expansion Upon Freezing
CRYSTAL LATTICE Water expands and becomes less dense when it freezes (density of liquid water 1 g/ml, density of ice 0.94 g/ml) The molecules in ice are less densely packed than in liquid water. Water is the most dense at 4°C. At temperatures below 4°C , particles of water begin to move apart slightly. Because water expands further when it freezes, ice is less dense than liquid water.

16. The hydrogen bonds that form in the ice create a lattice
structure, and the resulting extra space enables the ice to act
as insulation.
Many fish and aquatic plants can survive a cold winter
because the layer of ice that forms at the top of a lake
insulates the water below and prevents the lake from
freezing solid.

17. Versatility as a Solvent
A solution is a mixture in which one or more substances are evenly distributed in another substance. The polarity of water enables many substances to dissolve in water.

18. Many compounds dissolve in water
A solution is formed when one substance dissolves in another.
A solution is a homogeneous
mixture.
Solvents dissolve other
substances.
Solutes dissolve in a solvent.
solution
Solutions—a mixture that is the same throughout (homogeneous)
Solvents—substance present in greatest concentration; dissolves other substances
Solutes—substance present in lower concentration; dissolves in solvent
The solvent is the substance that is present in the greatest amount, and is the substance that dissolves solutes.
The solute is the substance being dissolved. 5

19. Example: If a crystal of table salt is placed in water, sodium and chloride ions on the surface of the crystal are attracted to the polar water molecules.

20. Universal Solvent
Like a magnet that pulls on things that are magnetic, water pulls on things that are electrically charged. Magnets have north & south poles, water has positive and negative poles and thus called a polar solvent. Since unlike charges attract, the negative end of water will be attracted to the positive sodium ion. The positive end of water will be attracted to the negative chloride ion. Since water is always in motion, it will pull on the ionic compound and move the ions away from each other. This dissolves the ionic compound.
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Since unlike charges attract, the negative end of water will be attracted to the positive sodium ion. The positive end of water will be attracted to the negative chloride ion. Since water is always in motion, it will pull on the ionic compound and move the ions away from each other. This dissolves the ionic compound.

21. Ionic compounds and polar molecules dissolve best in
water.
Nonpolar molecules, however, do not dissolve well in
Water’s ability to dissolve many substances enables
it to deliver essential nutrients to cells in plants,
animals and other organisms.

22. SC.912.L18.12 Properties of water that contribute to earth's suitability as an environment for life
Property of water
Contribution to earth’s suitability as an environment for life
Cohesive behavior
Water molecules have strong cohesion. Because of cohesion, water molecules remain join together as they move within or between the cells.
Because of cohesion, water and other liquids form thin films and drops, and flows upward against the force of gravity through the stem of a plant.
Ability to moderate
Temperatures
The high specific heat of water helps keep aquatic environments at fairly stable temperatures. The high specific heat of water also helps your body maintain a constant internal environment.
Large bodies of water, such as oceans and lakes, can absorb large amounts of heat with only small changes in temperature. This protects organisms living within from drastic changes in temperature.
Expansion upon
freezing
The lower density of water in the solid state than the liquid state allows ice to form at the surface of aquatic habitats, leaving a liquid environment beneath.
The layer of ice may prevent the deeper water from freezing
Versatility as a solvent
The polar nature of water molecules makes water an excellent solvent. This is important because many substances needed by cells enter the cell while dissolved in water.
Many of the chemical reactions take place in a water-based environment.

23. 1. A florist places a bouquet of white carnations in water containing blue dye. After a time, the flowers turn blue. What process helped the carnations to change color?
A. water’s ability to form crystals
B. ability of H2O to dissolve NaCl
C. cohesion and adhesion of water molecules
D. formation of covalent bonds between hydrogen and oxygen molecules

24. 2. Which of these statements correctly explains why water is a good solvent for many ionic compounds?
F. Water is a polar compound.
G. Water is an ionic compound.
H. Water molecules are nonpolar.
I. Water molecules completely separate into ions in solution.

25. 3. What is the attractive force between two of the same kind of particle?
A. adhesion
B. capillary action
C. cohesion
D. polarity

26. 4. Which of the following is not a unique property of water?
F. Water molecules stick together by cohesion.
G. Frozen water is less dense than liquid water.
H. Water molecules stick to other polar substances.
I. Hydrogen bonds allow water to heat and cool very quickly.

27. 5. Water has the ability to store heat longer than other substances
5. Water has the ability to store heat longer than other substances. What benefit does
this property of water provide to organisms?
A. It provides the ability to dissolve nonpolar compounds.
B. It provides the appropriate catalyst for chemical reactions.
C. It enables organisms to function with a higher cellular pH.
D. It allows organisms to maintain a stable internal temperature.

28. 6. Many fish and aquatic plants can survive a cold winter because the layer of ice that forms at the top of a lake insulates the water below and prevents the lake from freezing solid. What unique property of water contributes to this effect?
F. Water absorbs heat when it evaporates and forms a gas.
G. Water expands and becomes less dense when it freezes.
H. Water molecules completely separate into ions in solution.
I. Water forms hydrogen bonds with ions and other polar substances.

29. 7. Water is essential for life
7. Water is essential for life. Its special properties make water the single most important molecule in plant life.
Which of the following properties of water enables it to move from the roots to the
leaves of plants?
A. Water expands as it freezes.
B. Water is an excellent solvent.
C. Water exhibits cohesive behavior.
D. Water is able to moderate temperatures.