1. Properties of Water

2. Chemical Bonds
In a water molecule, each hydrogen atom forms a single covalent bond with the oxygen atom.
The chemical bond in which electrons are shared between atoms is called a covalent bond. In a water molecule, each hydrogen atom shares two electrons with the oxygen atom.

3. Covalent Bonds in the water molecule means electrons are shared between the Oxygen and Hydrogen atoms

4. Non-Polar Molecules
Covalent Bonds that have equal sharing of electrons make Non-Polar Molecules
E.g. Carbon Dioxide (CO2)
covalent bonds
Oxygen atom (O)
Carbon atom (C)
Carbon dioxide (CO2 )

5. Polar Bonds: unequal sharing of electrons
A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms. The oxygen end has a slight negative charge and the hydrogen is slightly positive
(-)
(+)
(+)

6. Because oxygen has 8 protons in its nucleus and hydrogen only has 1, oxygen has a stronger attraction for electrons than hydrogen.
Hydrogen
Oxygen

7. Draw this “froggy faced” water molecule

8. Chemical Bonds
Van der Waals Forces: A slight attraction that develops between the oppositely charged areas of nearby molecules

9. Chemical Bonds
Although van der Waals forces are not as strong as ionic bonds or covalent bonds, they can hold molecules together, especially when there are millions of molecules or the molecules are very large.

10. Chemical Bonds
Weak forces form between the molecules on the surface of a gecko’s foot and the molecules on the surface of the wall.
The combined strength of all these weak forces allows the gecko to grip the wall.
Photo Credit: top: Kellar Autumn & Ed Florance; bottom: © Mark Moffett/Minden Pictures, Inc.

11. Hydrogen Bonds
A type of van der Waals force, Hydrogen Bonds are between Hydrogen and another atom & create weak attractions between oppositely charged areas of a molecule
Hydrogen “Bonding” between water molecules gives water some unique properties

12. Hydrogen Bond
- Because of their partial positive and negative charges, polar molecules like water can attract each other.
hydrogen bonds (1: 17 , great overview of H bonds)

13. Example: Water molecules
Hydrogen bonds are not as strong as covalent or ionic bonds.
Draw this on your notes

14. Example: DNA molecules are held together on their inside by billions of weak Hydrogen Bonds

15. Hydrogen Bonds: weak polar covalent “bonds”

16. A single water molecule may be involved in as many as four hydrogen bonds at a time.
Water’s ability to form multiple hydrogen bonds is responsible for many of its special properties
The solid form of water (ice) floats because of the internal spaces created by hydrogen bonds

18. Water and Energy Storage
Water absorbs heat more slowly & keeps its heat energy longer (cools off more slowly) than many other substances because of it’s Hydrogen bonds. This affects Earth’s weather patterns- water absorbs heat when its hot, then releases heat when its cold so air temperatures are more stable near large bodies of water

19. Fish love water’s unique properties!

20. Water and Energy
Water can absorb a lot of energy in the form of heat because of its Hydrogen bonds
This means it takes a lot of energy and time to heat & boil water because more is needed to break the water to water attractive forces created by hydrogen bonds

21. Water and Energy
Water releases a lot of energy when it cools down & absorbs a lot of energy as it heats up
Organisms use this fact to cool their bodies: Water on the skin carries away heat when the water evaporates into the air

22. Cohesion is an attraction between molecules of the same substance.
Because of hydrogen bonds, water is extremely cohesive; water molecules like other water molecules!
Water’s cohesion causes water molecules on its surface to be drawn inward, towards each other. This is why drops of water form
beads on smooth surfaces.

23. Surface Tension Surface Tension is a type of cohesion
Surface Tension (Cohesion) explains why some insects and spiders can walk on a pond's surface.

24. Cohesion and Surface Tension
-On the surface of a cup of water, there are few water molecules, so each molecule is very strongly attracted to it’s neighbor. This creates Surface Tension
-Deep inside the cup, there
are many more water
molecules. Each molecule
has many neighbors, so its
attraction to each neighbor is
less strong (weaker)
Inside a cup of water

25. Adhesion is an attraction between molecules of different substances.
E.g. water and glass
The surface of water in a glass graduated cylinder dips in the center because adhesion between water molecules and glass molecules is stronger than cohesion between water molecules.

26. Adhesion between water and glass causes water to rise in a narrow tube against the force of gravity.
This effect is called capillary action.

27. Capillary action, caused by water’s attraction to plant surfaces (adhesion) draws water out of the roots of a plant and up into its stems and leaves.
Cohesion (attraction of water to water) holds the column of water together as it rises.

28. Draw this on the back of your notes:
Adhesion: water attracted to other things
Cohesion: water to water attraction
Adhesion: water attracted to other things

29. Properties of Water Videos
The Properties of Water (4:12 H2O in living things biology)
Water Structure and Hydrogen Bonding (3:06, cells need water, covalent bonds, + & - ends of H2O, )
hydrogen bonds (1: 17 , great overview of H bonds)
Amoeba sisters Properties of Water (6:50 H-bonds, transport in trees-ad&cohesion, walking on water, Universal solvent, floating ice, specific heat, evaporative cooling, )

30. Write these on the back of your notes Solutions and Suspensions
A mixture is made of two or more things (elements or compounds) that are physically mixed but not chemically combined
Two types of mixtures can be
made with water:
Solutions and Suspensions

31. Write these on the back of your notes Solutions and Suspensions
1. Solution- a type of mixture of two or more substances in which the particles of the substances are evenly spread out or distributed

32. Water is the Universal Solvent
Because water is a polar molecule, many things dissolve in water
Solvent- dissolving agent of a solution; its present in the larger amount: there’s always more solvent
Example: water
Solute- substance dissolved in the solvent; there’s less amount of solute
Example: Kool-aid

33. Solvent and Solute
Solute = Sugar
Solvent

34. Solutions
When a crystal of table salt is placed in warm water, sodium and chloride ions are attracted to the polar water molecules.
Cl -
Cl -
Na+
When an ionic compound such as sodium chloride is placed in water, water molecules surround and separate the positive and negative ions.
Na+
Water
Water
Ion: + or –
charged atom
or molecule

35. Ions break away from the crystal and are surrounded by water molecules.
Cl -
Cl -
Na+
Na+
Water
Water
The ions gradually become evenly dispersed in the water, forming a solution of salt water

36. Polar water mixes well with other charged substances, like NaCl,
but water does NOT mix well with nonpolar (and therefore non-charged) substances, ex. Oil, CO2 (soda)

37. Water Loving and Fearing
Add these two words to your Vocab list for Ch 2
Hydrophilic means water loving
these substances dissolve in water since they are charged or polar, like water
e.g. NaCl  Na+ + Cl-
(hydro=water, philic=liking, phobic=fearing)
Hydrophobic means water “fearing”
these substances will NOT dissolve in water because they are nonpolar
e.g. oils
Add these two words to your Vocab list for Ch 2

38. How can we clean oils from our hands and clothes by using water?
Soaps have a split personality
They are long molecules with a polar (hydrophilic) end and non-polar (hydrophobic) end. The hydrophobic ends “run” away from water and “hides” inside a hydrophilic cover
Soap has a hydrophilic head that is in
contact with water and a center of
hydrophobic tails, which can be used to
isolate grime, which is mostly oil & dirt

39. How soaps work
The polar end allows soaps to dissolve in water while the non-polar end interacts with oils & move them away from the water
The water loving outside can now be washed away with water, carrying away their contained oil particles with them
Hydrophilic on the outside
Hydrophobic on the inside

40. Suspensions: mixture of water and non-dissolved material
Some materials do not dissolve when placed in water but are separate pieces in the liquid, some are so small that they do not settle out but can stay in suspension as long as it is moving
The movement of water molecules keeps the small particles suspended.

41. Suspensions in Biology
The blood that circulates through your body is mostly water, which contains many dissolved compounds.
-Blood also contains blood cells and other undissolved particles that remain in suspension as the blood moves through the body
When blood is taken out of circulation, blood cells settle to the to the bottom of a test tube

42. Write these on the back of your notes Acids, Bases, and pH
A water molecule can react to form hydrogen (H+) and hydroxide (OH-) ions.
Water’s pH is neutral because # H+ = # OH-
Water is neutral (pH=7) because the number of positive hydrogen ions (H+) made equals the number of negative hydroxide ions (OH-) made

43. pH scale: measurement system used to show the concentration of hydrogen ions (H+) in solution; pH ranges from 0 to 14

44. When H+ does NOT equal OH –
Write these on the back of your notes Acids, Bases, and pH
When H+ does NOT equal OH –
the pH is NOT in balance & we use the pH scale to show how acidic or basic the solution is

45. Write these on the back of your notes Acids, Bases, and pH
Properties of Acids & Bases
Acid Base
- More H More OH-
- pH is less than pH is greater than 7
pH < pH > 7

47. Water & the pH scale
Acid Precipitation is rain, snow, or fog that has a pH lower than 5.6, as low as 1.5.
It is created when water reacts with Sulfur and Nitrogen oxides created from burning fossil fuels to created Sulfuric and Nitric Acids.
These then lower pH in soils, ponds, and lakes which can then endanger natural ecosystems