1. Water and Its Properties Honors Biology Ms. Kim

2. Water One side is more positive One side is more negative
Water is composed of one atom of oxygen and two atoms of hydrogen held together by covalent bonds (H2O)
Water is a Polar Molecule  unequal distribution of charges
One side is more positive
One side is more negative
When water molecules are close, their opposite sides are attracted to each other because of polarity
This attraction between water molecules is responsible for most of the properties of water.

3. Polar and Nonpolar Molecules
Polar Molecule – Unequal distribution of charges
One side is more positive
One side is more negative
Dissolves in water
Ex: Water
Nonpolar Molecule – no separation of charge, so no positive or negative poles are formed.
Do not dissolve in water
Ex: CO2, O2, lipids
Think of the interaction of two magnets and how they either are attracted to each other or repel.

4. How do water molecules interact with each other?
Polar water molecules can be attracted to each other
The hydrogen atom with its’ partial positive charge (+) is attracted to the oxygen atom (partial negative charge) of a different water molecule!
This is known as a hydrogen bond

5. Hydrogen Bonds Bonding between molecules
Very weak, but very important for the various
characteristics of of water…

6. Covalent bonds internally hold a water molecules together
Different water molecules are held together by hydrogen bonds – very weak bonds
Covalent
Hydrogen

7. 5 Characteristics of Water
1. Cohesion 2. Adhesion 3. High Specific Heat 4. Less Dense as a Solid 5. Water is a terrific solvent

8. Water Properties **H-bonding is responsible for these properties
1. Cohesion (“co-” means “together”)
the attraction between molecules of the same substance (water)
Tendency of molecules of the SAME “kind” to stick together
2. Surface Tension:
Measure of how difficult it is to stretch or break the surface of a liquid/ resist an external force.
H2O has high surface tension
Due to H-bonds

9. Water “sticks” to itself

10. Surface tension another type of cohesion
a measure of how difficult it is to stretch or break the surface of a liquid
Water molecules form a “barrier” by H-bonding together
Water does NOT pull apart very easily  acts like elastic

11. 2. Adhesion
Adhesion = The type of attraction that happens between two different molecules
Glass, soil, plant tissue, cotton, etc.
Forms stronger bonds than cohesion
Example:
Meniscus forming on graduated
cylinder!
Capillary action- seen in plants,
trees and with straws too!

13. Cohesion & Adhesion Acting Together
Helps pull water up through the microscopic vessels of plants is Called capillary action

14. Another Example of Cohesion and Adhesion…

15. High Specific Heat
The temperature of water does not increase or decrease easily
Water has to absorb more heat energy to increase overall temperature compared to other compounds
Ex: Lake Michigan is really cold until ~ August…it takes a long time to warm up!!
Helps to regulate cell temperatures in organisms
Due to the fact that the molecules hold each other together, the temperature of water does not rise or fall very easily

16. Water has a high specific heat so its temperature does NOT fluctuate very much  allows life to live in water
moderate Earth's climate by buffering large fluctuations in temperature.

17. How come icebergs float?

18. 4. Low Density in Solid Form
Allows for insulation of bodies of water by floating ice
Solid water (i.e.-ice)
Is less dense than liquid water
Floats in liquid water
Since ice floats in water 
Life can exist under frozen surfaces of lakes/polar seas

19. Ice floats because ice is less dense than liquid water!
This is because the H bonds hold the water molecules farther apart than in liquid water

20. The hydrogen bonds in ice
Are more “ordered” than in liquid water, making ice less dense
Liquid water
Hydrogen bonds constantly break and re-form
Ice
Hydrogen bonds are stable

21. 5. Water as a Solvent What is a solution?
A solution is a mixture of substances looks the same throughout
Made up of a solute and a solvent
Water is a GREAT solvent (Water is the universal solvent)
Solute – gets dissolved (Hot Cocoa mix)
Solvent – does the dissolving (Water)
Solution – uniform mixture of two or more substances

22. Hydrophilic and Hydrophobic Substances
A hydrophilic substance
Has an affinity for water
Water “loving”
Dissolves in water
Example: salt and sugar
A hydrophobic substance
Does not have an affinity for water
Water “fearing”
Does NOT dissolve in water
Example: Oil

23. REVIEW Where is the Polar Covalent Bond in water?
What is the difference btw a “POLAR COVALENT BOND” and a “NONPOLAR COVALENT BOND?

24. Acids and Bases
An acid
compound that releases/donates a proton (H+) when dissolved in water
Increases H+ concentration in solution
Ex: HCl
A base
compound that accepts H+ and removes them from a solution
Is any substance that reduces the hydrogen ion concentration of a solution
The more basic the solution, the higher the OH- concentration
Ex: NaOH pH
Measure of acidity or alkalinity of an aqueous solution

25. What is the pH scale? Identifies acids and bases
Indicates concentration of H+ ions in a solution
pH 7 = Neutral = concentration of H+ and OH- are equal

26. How do you read the pH scale?
pH of 7
Neutral
Concentration of OH- and H+ are equal
Ex – Water
pH 1 – 6.5
Acid
More H+ than OH-
Ex – Lemon juice / HCl
pH 7.5 – 14
Base
More OH- than H+
Ex – Baking soda / ammonia

27. What is a buffer? Buffers prevent drastic changes in pH
Buffers: weak acids or bases that can react with strong acids or bases to prevent sudden changes in pH
Why are buffers important?
Key in regulating our urinary, circulatory, and blood pH
Necessary in maintaining homeostasis
Buffers prevent our blood from becoming too acidic, our lungs/muscles from becoming over saturated in CO2

28. the lower the pH the stronger the acid
the higher the pH the stronger the base
pH 7.0 is neutral

30. Acid precipitation Can damage life in Earth’s ecosystems More acidic1 2 3 4 5 6 7 8 9 10 11 12 13 14
More acidic
Acid rain
Normal rain
More basic

31. Thermal Energy
Thermal energy is the energy that is generated and measured by heat.