1. Hydrogen Bonding Hydrogen bonding
Hydrogen bonds + H
 –
Hydrogen Bonding
Hydrogen bonding
A force of attraction between a partially positive hydrogen atom in a molecule and another molecule or atom with a partial negative charge

2. 1) Which of the following is an example of a hydrogen bond? A) CH4
B) H2O
C) NaCl
D) H2
E) a, b, and d can form hydrogen bonds
2) What is the maximum number of hydrogen bonds a water molecule can form with neighboring water molecules?
A) four
B) five
C) one
D) two
E) three E
A (these bonds are constantly changing – and may also depend on the state of water)

3. Water (H2O) Polar molecule Structure of Water two hydrogen atoms
one oxygen atom
Polar molecule
one side partially negative and the other side partially positive

4. Concept check
Why is it highly unlikely that two neighboring water molecules will be arranged like this?
What will be the effect on the properties of the water molecule if oxygen and hydrogen had equal electronegativity?
- the hydrogen ions of one water molecule with their partially positive charge will repel the hydrogen atoms of the adjacent molecule
- the covalent bonds of water molecules would not be polar & water molecules would not form hydrogen bonds with each other

5. Properties of Water: 1) Cohesion & Adhesion
Cohesion – attraction between molecules of the same substance
drop of water on penny
surface tension
Adhesion – attractive force between particles of different substances
capillary action

6. Water Transport in Plants

7. Properties of water 2) Temperature moderation
Water bodies absorb, store and release heat; moderate climate
absorb heat from warmer air
release the stored heat to cooler air

8. Properties of water 2) Temperature moderation Heat ≠ temperature
Water has a high specific heat
Is the amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1ºC
Takes a lot of energy to change temperature of water
Why? H-bonds
Heat is absorbed when hydrogen bonds break
Heat is released when hydrogen bonds form
Minimizes temperature fluctuations to within limits that permit life
Heat s a form of energy that can be transferred from one point to another without the transfer of matter
Temperature is the measure of how hot or cold an object is

9. 2) Temperature moderation
Properties of water
2) Temperature moderation
Evaporation
Is the transformation of a substance from a liquid to a gas
Heat of vaporization
Is the quantity of heat a liquid must absorb for 1 gram of it to be converted from a liquid to a gas
Evaporative cooling
Is due to water’s high heat of vaporization
Allows water to cool a surface
Ex: sweating (explain)

10. H- bonds constantly break and re-form
Hydrogen bond
Ice
H- bonds are stable
Liquid water
H- bonds constantly break and re-form
3) Insulation of water bodies by floating ice
Ice is less dense than water
Why? H-bonds
What would happen if ice sank?

11. Properties of water 4) Universal solvent
Solution – homogeneous mixture of two of more substances
solute – substance being dissolved
solvent – substance the solute is dissolving into
Aqueous solution – water is solvent

12. Negative oxygen regions of polar water molecules are attracted to sodium cations (Na+).
Cl – –
Na+
Positive hydrogen regions of water molecules cling to chloride anions (Cl–).
Cl–

13. Properties of water 4) Universal solvent
dissolves other polar molecules
Hydrophilic, “water loving,” substances are attracted to water
polar molecules
ionic molecules
Hydrophobic, “water fearing,” substances do not have an affinity for water
non-polar molecules

14. Concept Check
Describe how properties of water contribute to the upwards movement of water in a tree
Explain the saying “its not the heat, it’s the humidity.”
How can the freezing of water crack boulders?
A water strider(which can walk on water) has legs that are coated with a Hydrophobic substance.
What is the benefit of this?
What would happen if the substance were hydrophilic?
Hydrogen bonds hold water molecules together. Cohesion forces helps the chain of water molecules move upwards against gravity and adhesion forces between the water molecules and the walls of the Xylem also help water move against gravity
Humidity hampers / deters cooling by suppressing the evaporation of sweat from the body
Water expands as it freezes as the water molecules move farther apart as it forms ice crystals. If there is water in the crevice of a boulder, the expansion of the water as it freezes may cause the boulder to crack.
Hydrophobic substance repels water and prevents the legs from being coated with water and sinking. The hydrophilic substance will allow the striders legs to be coated with water hence breaking the surface tension of water and sinking

15. Solution concentration
A mole
Represents an exact number of molecules of a substance in a given mass
Molarity
Is the number of moles of solute per liter of solution

16. Acids and Bases Water can dissociateH
Hydronium
ion (H3O+)
Hydroxide
ion (OH–) + –
Figure on p. 53
of water dissociating
Water can dissociate
Into hydronium ions and hydroxide ions
Changes in the concentration of these ions
Can have a great affect on living organisms

17. Acids and Bases An acid A base
Is any substance that increases the hydrogen ion concentration of a solution
A base
Is any substance that reduces the hydrogen ion concentration of a solution

18. Acids and Bases
Increasingly Acidic
[H+] > [OH–]
Increasingly Basic
[H+] < [OH–]
Neutral
[H+] = [OH–]
Oven cleaner 1 2 3 4 5 6 7 8 9 10 11 12 13 14
pH Scale
Battery acid
Digestive (stomach)
juice, lemon juice
Vinegar, beer, wine,
cola
Tomato juice
Black coffee Rainwater
Urine
Pure water
Human blood
Seawater
Milk of magnesia
Household ammonia
Household bleach
Figure 3.8
The pH of a solution
Is determined by the relative concentration of hydrogen ions
Is low in an acid
Is high in a base

19. Acids and Bases
Each pH unit represents a tenfold difference in H+ and OH- concentrations.
It is this mathematical feature that makes the pH scale so compact.
A solution of pH 3 is not twice as acidic as a solution of pH 6, but a thousand times (10 x 10 x 10) more acidic.
Compared with a basic solution at pH 9, the same volume of an acidic solution at pH 4 has _____________ times as many hydrogen ions (H+).
100,000 or 105

20. Acids and Bases Organisms are picky about the pH. Buffers
Are substances that minimize changes in the concentrations of hydrogen and hydroxide ions in a solution
Consist of an acid-base pair that reversibly combines with hydrogen ions