1. CHEMICAL CONTEXT OF LIFE
CHAPTER 2

2. Chemical Benefits and Costs
Understanding of chemistry provides fertilizers, medicines, etc.
Chemical pollutants damage ecosystems

3. Bioremediation
Use of living organisms to withdraw harmful substances from the environment

4. Fundamental forms of matter Can’t be broken apart by normal means
Elements
Fundamental forms of matter
Can’t be broken apart by normal means
92 occur naturally on Earth

5. Most Common Elements in Living Organisms
Oxygen
Hydrogen
Carbon
Nitrogen

6. About 20 of the 92 elements are essential to life
Trace elements are required only in minute quantities
Deficiencies can be harmful

7. Nitrogen Deficiency in
Tomato Plants

8. Iodine Deficiency – Enlarged Thyroid Gland
Thyroid grows to abnormal size
Can be reversed with iodine rich diet
Daily intake of 0.15mg
Iodized salt has reduced incidence
Trace Elements

9. Chemical Terminology
Matter – anything that takes up space and has mass
Element - substances that cannot be broken down to by chemical reactions

10. Atomic Structure
Determines the
Behavior of an
Element

11. Atoms are the smallest unit having properties of an element.
Elements made of Atoms...
Atoms are the smallest unit having properties of an element.
3 Particles of an Atom
Protons (+ charge)
Electrons (- charge)
Neutrons (neutral charge)

12. Smallest particles that retain properties of an element
What are Atoms?
Smallest particles that retain properties of an element
Made up of subatomic particles:
Protons (+)
Electrons (-)
Neutrons (no charge)

13. Protons and Neutrons
packed tightly
in core - Atomic
Nucleus
Electrons move
along outer orbit
(speed of light)

14. Isotopes - differ in # neutrons
Lighter
Heavier
Mass Difference

15. Radioisotopes Have an unstable nucleus that emits energy and particles
Radioactive decay transforms radioisotope into a different element
Decay occurs at a fixed rate

16. Radioisotopes Carbon-12 and Carbon-14 are isotopes
Both types very common
Carbon-12 is very stable
Carbon 14 is unstable
Will disintegrate
5600 yrs
Emit radiation as it decays

17. Radioisotopes as Tracers
Tracer is substance with a radioisotope attached to it
Emissions from the tracer can be detected with special devices
Following movement of tracers is useful in many areas of biology

18. Thyroid Scan
Measures health of thyroid by detecting radioactive iodine taken up by thyroid gland
normal thyroid
enlarged
cancerous

19. Other Uses of Radioisotopes
Drive artificial pacemakers
Radiation therapy
Emissions from some radioisotopes can destroy cells. Some radioisotopes are used to kill small cancers.

20. What Determines Whether Atoms Will Interact?
The number and arrangement of their electrons

21. Electrons Carry a negative charge Repel one another
Are attracted to protons in the nucleus
Move in orbitals - volumes of space that surround the nucleus y Z X
When all p orbitals are full

22. Electron Cloud

23. Electron Orbitals Orbitals can hold up to two electrons
Atoms differ in the number of occupied orbitals
Orbitals closest to nucleus are lower energy and are filled first

24. Electron Vacancies Unfilled shells make atoms likely to react
Hydrogen, carbon, oxygen, and nitrogen all have vacancies in their outer shells
CARBON
6p+ , 6e-
NITROGEN
7p+ , 7e-
HYDROGEN
1p+ , 1e-

25. 2 elements bond
together to form
compounds

26. Sodium + Chlorine = Table Salt
Compound...
Substance consisting of 2 or more elements chemically combined
Sodium Chlorine = Table Salt

27. Chemical Bonds, Molecules,
& Compounds
Bond is union between electron structures of atoms
Atoms bond to form molecules
Molecules may contain atoms of only one element - O2
Molecules of compounds contain more than one element - H2O

28. Chemical Bookkeeping Use symbols for elements when writing formulas
Formula for glucose is C6H12O6
6 carbons
12 hydrogens
6 oxygens

29. Reactants ---> Products
Chemical Bookkeeping
Chemical equation shows reaction
Reactants ---> Products
Equation for photosynthesis:
6CO2 + 6H2O ---> + C6H12O H2O

30. Ionic Bonds Covalent Bonds Hydrogen Bonds
Important Bonds in
Biological Molecules
Ionic Bonds
Covalent Bonds
Hydrogen Bonds

31. Ion Formation
Atom has equal number of electrons and protons - no net charge
Atom loses electron(s), becomes positively charged ion
Atom gains electron(s), becomes negatively charged ion

32. Ionic Bonding One atom loses electrons, becomes positively charged ion
Another atom gains these electrons, becomes negatively charged ion
Charge difference attracts the two ions to each other

33. Formation of NaCl
Sodium atom (Na)
Outer shell has one electron
Chlorine atom (Cl)
Outer shell has seven electrons
Na transfers electron to Cl forming Na+ and Cl-
Ions remain together as NaCl

34. Formation of NaCl electron transfer SODIUM ATOM 11 p+ 11 e- CHLORINE
7mm
electron transfer
SODIUM
ATOM
11 p+
11 e-
CHLORINE
ATOM
17 p+
17 e-
CHLORINE
ION
17 p+
18 e-
SODIUM
ION
11 p+
10 e-
Fig. 2.10a, p. 26

35. Atoms share a pair or pairs of electrons to fill outermost shell
Covalent Bonding
Atoms share a pair or pairs of electrons to fill outermost shell
Single covalent bond
Double covalent bond
Triple covalent bond

36. Nonpolar Covalent Bonds
Atoms share electrons equally
Nuclei of atoms have same number of protons
Example: Hydrogen gas (H-H)

37. Polar Covalent Bonds
Number of protons in nuclei of participating atoms is NOT equal
Electrons spend more time near nucleus with most protons
Water - Electrons more attracted to O nucleus than to H nuclei

38. Hydrogen Bonding
Molecule held together by polar covalent bonds has no NET charge
However, atoms of the molecule carry different charges
Atom in one polar covalent molecule can be attracted to oppositely charged atom in another such molecule

39. Examples of Hydrogen Bonds
one
large
molecule
another
large
molecule
a large
molecule
twisted
back on
itself
Fig. 2.12, p. 27

40. Polarity Solvent Temperature-Stabilizing Cohesive
Properties of Water
Polarity
Solvent
Temperature-Stabilizing
Cohesive

41. 1. Water Structure Water is a polar molecule.
Oxygen has a partial negative charge
Hydrogen has a partial positive charge.

42. Water Is a Polar Covalent Molecule
Oxygen and hydrogen share electrons forming a covalent bond
Two molecules of water are joined by Hydrogen bonds O H H

43. Liquid Water H + + _ H + O H + O _ + H +

44. 2. Water as a Solvent Background information:
Solution: a homogenous mixture of two or more substances
Solvent: the dissolving agent
Solute: the dissolved substance
Aqueous solution: a solution where water is the solvent.

45. Water as a Solvent Water dissolves a lot of things!! Why??
The polarity of water separates and dissolves ions (positive or negatively charged!)
Other polar molecules behave in the same way!

46. Keeping Ions Separate = Dissolving Power
Spheres of Hydration
Na+
Cl– – +
Keeping Ions Separate = Dissolving Power

47. To Dissolve or Not to Dissolve?
Hydrophilic: A substance with an affinity/able to dissolve in water.
What kind of substances?
Hydrophobic: A substance that repels water/don’t dissolve.

48. Hydrophilic & Hydrophobic Substances
Hydrophilic substances
Polar
Hydrogen bond with water
Example: sugar
Hydrophobic substances
Nonpolar
Repelled by water
Example: oil

49. Cell Membrane

50. 3. Temperature-Stabilizing Effects
Liquid water can absorb much heat before its temperature rises
Why?
Much of the added energy disrupts hydrogen bonding rather than increasing the movement of molecules

51. Moderation of Temperature
Water is able to stabilize temperature because it has a HIGH specific heat.
Specific heat: the amount of heat that must be absorbed or lost for 1 g to change its temperature by 1º. (water takes a lot of energy)
Think of specific heat as a measure of how well a substance resists changing its temperature when it absorbs or releases heat.

52. Evaporation of Water
Large energy input can cause individual molecules of water to break free into air
As molecules break free, they carry away some energy (lower temperature)
Evaporative water loss is used by mammals to lower body temperature, cool oceans, etc.

53. Why Ice Floats
In ice, hydrogen bonds lock molecules in a lattice keeping them apart
Water molecules in lattice are spaced farther apart then those in liquid water
Ice is less dense than water

54. 4. Water Cohesion
Hydrogen bonding holds molecules in liquid water together
Creates surface tension
Allows water to move as continuous column upward through stems of plants

55. Hydrogen Ions: H+ Unbound protons Have important biological effects
Form when water ionizes

56. 0---------------------7-------------------14
The pH Scale
Measures H+ concentration of fluid
Change of 1 on scale means 10X change in H+ concentration
Highest H Lowest H+
Acidic Neutral Basic

57. Examples of pH Pure water is neutral with pH of 7.0 Acidic Basic
Stomach acid: pH
Lemon juice: pH 2.3
Basic
Seawater: pH
Baking soda: pH 9.0

58. Acids & Bases Acids Bases Donate H+ when dissolved in water
Acidic solutions have pH < 7
Bases
Accept H+ when dissolved in water
Acidic solutions have pH > 7

59. Weak and Strong Acids Weak acids Strong acids Reluctant H+ donors
Can also accept H after giving it up
Carbonic acid (H2CO3) is example
Strong acids
Completely give up H+ when dissolved
Hydrochloric acid (HCl) is example

60. Buffer Systems Minimize shifts in pH
Partnership between weak acid and base it forms when dissolved
Two work as pair to counter shifts in pH

61. Carbonic Acid-Bicarbonate Buffer System
When blood pH rises, carbonic acid dissociates to form bicarbonate and H+
H2C > HC03- + H+
When blood pH drops, bicarbonate binds H+ to form carbonic acid
HC H > H2C03