1. Chemistry and Properties of Water
AP Biology
Chemistry and
Properties of Water

2. Matter consists of chemical elements in pure form and in combinations called compounds
Organisms are composed of matter
Matter is anything that takes up space and has mass
Atoms are the basic units in chemicals
Matter is made up of elements
An element is a substance that cannot be broken down to other substances by chemical reactions
A compound is a substance consisting of two or more elements in a fixed ratio
A compound has characteristics different from those of its elements
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3. Table 2-1
Table 2-1

4. Electrons (– charge) form negative cloud and determine
Fig. 2-UN3
Nucleus
Protons (+ charge)
determine element
Electrons (– charge) form negative cloud
and determine
chemical behavior
Neutrons (no charge)
determine isotope
Atom

5. Ionic bond Electron transfer forms ions Na Sodium atom Cl
Fig. 2-UN6
Ionic bond
Electron
transfer
forms ions Na
Sodium atom Cl
Chlorine atom
Na+
Sodium ion
(a cation)
Cl–
Chloride ion
(an anion)

6. 1H 2He 3Li 4Be 5B 6C 7N 8O 9F 10Ne 11Na 12Mg 13Al 14Si 15P 16S 17Cl
Fig. 2-9
Hydrogen 1H 2
Atomic number
Helium
2He He
Atomic mass
4.00
First
shell
Element symbol
Electron-
distribution
diagram
Lithium
3Li
Beryllium
4Be
Boron 5B
Carbon 6C
Nitrogen 7N
Oxygen 8O
Fluorine 9F
Neon
10Ne
Second
shell
Sodium
11Na
Magnesium
12Mg
Aluminum
13Al
Silicon
14Si
Phosphorus
15P
Sulfur
16S
Chlorine
17Cl
Argon
18Ar
Figure 2.9 Electron-distribution diagrams for the first 18 elements in the periodic table
Third
shell

7. C Atomic Symbols 12 6 Carbon Each element represented by
unique atomic symbol
One or two letters
First letter capitalized
Superscripted number before:
Represents mass number
Count of protons plus count of neutrons
Subscripted number before
Represents to atomic number
Number of protons in nucleus
Mass Number 12 6
Carbon C
Atomic Number
Atomic Symbol

8. Isotopes C C C Carbon 12 Carbon 13 Carbon 14 Isotopes:
Atoms of the same element with a differing numbers of neutrons
Some isotopes spontaneously decay
Radioactive
Give off energy in the form of rays and subatomic particles
Can be used as tracers
Mutagenic – Can cause cancer 12 6
Carbon 12 C 13 6
Carbon 13 C 14 6
Carbon 14 C

11. NaCl

12. NaCl in Solution

13. Covalent Bonds formed when atoms share electrons
sharing can be unequal

15. Neon, with two filled shells (10 electrons) (a) Electron-distribution
Fig
Neon, with two filled shells (10 electrons)
(a)
Electron-distribution
diagram
First shell
Second shell
(b)
Separate electron
orbitals x y z
1s orbital
2s orbital
Three 2p orbitals
Figure 2.10 Electron orbitals
(c)
Superimposed electron
orbitals
1s, 2s, and 2p orbitals

16. Hydrogen Bonds
A hydrogen bond forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom
In living cells, the electronegative partners are usually oxygen or nitrogen atoms
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17.   + Water (H2O) + Hydrogen bond   Ammonia (NH3) + + +
Fig. 2-16
  +
Water (H2O) +
Hydrogen bond
 
Ammonia (NH3)
Figure 2.16 A hydrogen bond + + +

18. Overview: The Molecule That Supports All of Life
Water is the biological medium on Earth
All living organisms require water more than any other substance
Most cells are surrounded by water, and cells themselves are about 70–95% water
The abundance of water is the main reason the Earth is habitable
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19. The polarity of water molecules results in hydrogen bonding
The water molecule is a polar molecule: The opposite ends have opposite charges
Polarity allows water molecules to form hydrogen bonds with each other
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20. H O H  –  +  –  +  –  +  –  + Hydrogen bond —— —— Fig. 3-2
Figure 3.2 Hydrogen bonds between water molecules
 –
 +

21. Four emergent properties of water contribute to Earth’s fitness for life
Four of water’s properties that facilitate an environment for life are:
Cohesive behavior
Ability to moderate temperature
Expansion upon freezing
Versatility as a solvent
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22. Cohesion
Collectively, hydrogen bonds hold water molecules together, a phenomenon called cohesion
Cohesion helps the transport of water against gravity in plants
Adhesion is an attraction between different substances, for example, between water and plant cell walls
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

23. Adhesion Water-conducting cells Direction Cohesion of water movement
Fig. 3-3
Adhesion
Water-conducting
cells
Direction
of water
movement
Cohesion
Figure 3.3 Water transport in plants
150 µm

24. Surface tension is related to cohesion
Surface tension is a measure of how hard it is to break the surface of a liquid
Surface tension is related to cohesion
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

25. Fig. 3-4
Figure 3.4 Walking on water

26. Water’s High Specific Heat
The specific heat of a substance is the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1ºC
The specific heat of water is 1 cal/g/ºC
Water resists changing its temperature because of its high specific heat
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

27. Insulation of Bodies of Water by Floating Ice
Ice floats in liquid water because hydrogen bonds in ice are more “ordered,” making ice less dense
Water reaches its greatest density at 4°C
If ice sank, all bodies of water would eventually freeze solid, making life impossible on Earth
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

28. Heat Capacity Water has a high heat capacity
Temperature = rate of vibration of molecules
Apply heat to liquid
Molecules bounce faster
Increases temperature
But, when heat applied to water
Hydrogen bonds restrain bouncing
Temperature rises more slowly per unit heat
Water at a given temp. has more heat than most liquids
Thermal inertia – resistance to temperature change
More heat required to raise water one degree than most other liquids (1 calorie per gram)
Also, more heat is extracted/released when lowering water one degree than most other liquids

29. Properties of Water: Heat of Vaporization
High heat of vaporization
To raise water from 98 to 99 ºC; ~1 calorie
To raise water from 99 to 100 ºC; ~1 calorie
However, large numbers of hydrogen bonds must be broken to evaporate water
To raise water from 100 to 101 ºC; ~540 calories!
This is why sweating (and panting) cools
Evaporative cooling is best when humidity is low because evaporation occurs rapidly
Evaporative cooling works poorest when humidity is high because evaporation occurs slowly

30. Evaporative Cooling of Animals

31. Heat of Fusion Heat of fusion (melting)
To raise ice from -2 to -1 ºC; ~1 calorie
To raise water from -1 to 0 ºC; ~1 calorie
To raise water from 0 to 1 ºC; ~80 calories!
This is why ice at 0 ºC keeps stuff cold MUCH longer than water at 1 ºC
This is why ice is used for cooling
NOT because ice is cold
But because it absorbs so much heat before it will warm by one degree

32. Heat Content of Water at Various Temperatures

33. Properties of Water: Uniqueness of Ice
Frozen water less dense than liquid water
Otherwise, oceans and deep lakes would fill with ice from the bottom up
Ice acts as an insulator on top of a frozen body of water
Melting ice draws heat from the environment

34. A Pond in Winter

35. Density of Water at Various Temperatures

36. Hydrogen bonds are stable Liquid water
Fig. 3-6a
Hydrogen
bond
Figure 3.6 Ice: crystalline structure and floating barrier
Ice
Hydrogen bonds are stable
Liquid water
Hydrogen bonds break and re-form

37. Hydrophilic and Hydrophobic Substances
A hydrophilic substance is one that has an affinity for water
A hydrophobic substance is one that does not have an affinity for water
Oil molecules are hydrophobic because they have relatively nonpolar bonds
A colloid is a stable suspension of fine particles in a liquid
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

38. Properties of Water: Water as a Solvent
Solutions consist of:
A solvent (the most abundant part) and
A solute (less abundant part) that is dissolved in the solvent
Polar compounds readily dissolve; hydrophilic
Nonpolar compounds dissolve only slightly; hydrophobic
Ionic compounds dissociate in water
Na+
Attracted to negative (O) end of H2O
Each Na+ completely surrounded by H2O
Cl-
Attracted to positive (H2) end of H2O
Each Cl- completely surrounded by H2O

39. pH of Water: Acids Acids
Dissociate in water and release hydrogen ions (H+)
Sour to taste
Hydrochloric acid (stomach acid) is a gas with symbol HCl
In water, it dissociates into H+ and Cl-
Dissociation of HCl is almost total, therefore it is a strong acid

40. pH of Water: Bases Bases:
Either take up hydrogen ions (H+) or release hydroxide ions (OH-)
Bitter to taste
Sodium hydroxide (drain cleaner) is a solid with symbol NaOH
In water, it dissociates into Na+ and OH-
Dissociation of NaOH is almost total, therefore it is a strong base

41. pH Scale
pH scale used to indicate acidity and alkalinity of a solution.
Values range from 0-14
0 to <7 = Acidic
7 = Neutral
>7 to 14 = Basic (or alkaline)
Logarithmic Scale
Each unit change in pH represents a change of 10X
pH of 4 is 10X as acidic as pH of 5
pH of 10 is 100X more basic than pH of 8

42. The pH Scale

43. Buffers and pH
When H+ is added to pure water at pH 7, pH goes down and water becomes acidic
When OH- is added to pure water at pH 7, pH goes up and water becomes alkaline
Buffers are solutes in water that resist change in pH
When H+ is added, buffer may absorb, or counter by adding OH-
When OH- is added, buffer may absorb, or counter by adding H+

44. Biology, 9th ed,Sylvia Mader
Chapter 02
Buffers in Biology
Health of organisms requires maintaining pH of body fluids within narrow limits
Human blood normally 7.4 (slightly alkaline)
Many foods and metabolic processes add or subtract H+ or OH- ions
Reducing blood pH to 7.0 results in acidosis
Increasing blood pH to 7.8 results in alkalosis
Both life threatening situations
Bicarbonate ion (-HCO3) in blood buffers pH to 7.4
Basic Chemistry

45. Review Chemical Elements Atoms Isotopes Molecules and Compounds
Chemical Bonding
Ionic and Covalent
Hydrogen
Properties of Water
Acids and Bases