1. The Chemical Basis of Life
Chapter 2
The Chemical Basis of Life

2. Nature’s Chemical Language
Nature’s Chemical Language
Both male and female rattlebox moths produce chemicals important for mating and defense.
The compound produced during mating allows the moths to communicate using chemicals

3. Chemicals play many more roles in life than signaling making up our bodies, those of other organisms, and the physical environment

4. ELEMENTS, ATOMS, AND MOLECULES
2.1 Living organisms are composed of about 25 chemical elements
Matter
is what life is composed of.
occupies space.  
has mass.  
is composed of elements.

5. About 25 different chemical elements are essential to life
Carbon, hydrogen, oxygen, and nitrogen make up the bulk of living matter
Table 2.1

7. Ex. Fluorine, zinc, manganese, & iodine
CONNECTION
2.2: Trace elements are common additives to food and water
Trace elements are essential to life, but occur in minute amounts
Ex. Fluorine, zinc, manganese, & iodine
Dietary deficiencies in trace elements can cause various physiological conditions
Figure 2.2A

8. Trace elements are essential to human health
Trace elements are essential to human health
And may be added to food or water
Figure 2.2B

9. 2.3 Elements can combine to form compounds
2.3 Elements can combine to form compounds
Chemical elements combine in fixed ratios to form compounds.
Compound-contains two or more elements in a fixed ratio.  
Ex. H2O
Sodium
Chlorine
Sodium Chloride
Figure 2.3

10. 2.4 Atoms consist of protons, neutrons, and electrons
2.4 Atoms consist of protons, neutrons, and electrons
The smallest particle of matter that still retains the properties of an element is an atom

11. Subatomic Particles An atom is made up of protons and neutrons
Subatomic Particles
An atom is made up of protons and neutrons
The nucleus contains protons and neutrons and is surrounded by electrons arranged in electron shells that orbit around the nucleus. – –
Electron
cloud
2e– + + + +
Nucleus 2 +
Protons
Mass number = 4 2
Neutrons
Figure 2.4A 2 –
Electrons

12. Differences in Elements
Differences in Elements
Atoms of each element
Are distinguished by a specific number of protons
Electron cloud
6e– + +
Nucleus 6 +
Protons
Mass number = 12 6
Neutrons
Figure 2.4B 6 –
Electrons

13. Atomic Number-the number of protons in an element
Mass Number-the sum of the protons and neutrons in the nucleus
Atomic Mass-the sum of the protons and neutrons in the nucleus
Isotope-have same number of protons and electrons, but have different numbers of neutrons.

14. Isotopes The number of neutrons in an atom may vary
Isotopes
The number of neutrons in an atom may vary
Variant forms of an element are called isotopes
Some isotopes are radioactive and decay.
Table 2.4

15. 2.5 Radioactive isotopes can help or harm us
CONNECTION
2.5 Radioactive isotopes can help or harm us
Radioactive isotopes are useful as tracers for monitoring the fate of atoms in living organisms
The energy emitted by radioactive isotopes can break chemical bonds and cause molecular damage in cells.

16. Basic Research Biologists often use radioactive tracers
Basic Research
Biologists often use radioactive tracers
To follow molecules as they undergo chemical changes in an organism

17. Medical Diagnosis
Radioactive isotopes can be used in conjunction with PET scans to diagnose a patient.
Figure 2.5A
Figure 2.5B

18. Dangers Radioactive isotopes have many beneficial uses
Dangers
Radioactive isotopes have many beneficial uses
But uncontrolled exposure to them can harm living organisms

19. Outermost electron shell (can hold 8 electrons)
2.6 Electron arrangement determines the chemical properties of an atom
Electrons in an atom are arranged in shells, which may contain different numbers of electrons
When full, the innermost electron shell of an atom contains 2 electrons, and the outermost shell contains 8 electrons.
Outermost electron shell (can hold 8 electrons)
First electron shell (can hold 2 electrons)
Electron
Hydrogen (H)
Atomic number = 1
Carbon (C)
Atomic number = 6
Nitrogen (N)
Atomic number = 7
Oxygen (O)
Atomic number = 8
Figure 2.6

20. The farther an electron is from the nucleus, the greater its energy.
Atoms whose shells are not full tend to interact with other atoms and gain, lose, or share electrons
These interactions form chemical bonds

21. Sodium chloride (NaCl)
2.7 Ionic bonds are attractions between ions of opposite charge
When atoms gain or lose electrons charged atoms called ions are created
An electrical attraction between ions with opposite charges results in an ionic bond – –
Transfer of electron + – Na Cl Na Cl
Na Sodium atom
Cl Chlorine atom
Na+ Sodium ion
Cl– Chloride ion
Figure 2.7A
Sodium chloride (NaCl)

22. Table salt is formed when sodium gives an electron to chlorine.
Table salt is formed when sodium gives an electron to chlorine.
Na+
Cl–
Figure 2.7B

23. 2.8 Covalent bonds join atoms into molecules through electron sharing
2.8 Covalent bonds join atoms into molecules through electron sharing
In covalent bonds
Two atoms share one or more pairs of outer shell electrons, forming molecules

24. Molecules can be represented in many ways
Molecules can be represented in many ways
Table 2.8

25. 2.9 Unequal electron sharing creates polar molecules
2.9 Unequal electron sharing creates polar molecules
A molecule is nonpolar
When its covalently bonded atoms share electrons equally

26. In a polar covalent bond electrons are shared unequally between atoms, creating a polar molecule
The oxygen atom of a water molecule  is more electronegative than the hydrogen atoms.
(–)
(–) O H H
(+)
(+)
Figure 2.9

27. Ex. Many fabrics are coated with a "water-repellent" chemical that causes water to bead on the fabric instead of soaking in. This probably occurs because the coating is neutral and repels the positive and negative ends of the water molecules.

28. 2.10 Hydrogen bonds are weak bonds important in the chemistry of life
2.10 Hydrogen bonds are weak bonds important in the chemistry of life
The charged regions on water molecules are attracted to the oppositely charged regions on nearby molecules

29. Hydrogen bonds are weak bonds that are not strong enough to hold atoms together to form molecules but are strong enough to form bridges between molecules.  
(–)
Hydrogen bond
(+) H O
(–)
(+) H
(–)
(+)
(–)
(+)
Figure 2.10

30. The hydrogen atoms of a water molecule are bonded to the oxygen atom by polar covalent bonds, whereas neighboring water molecules are held together by hydrogen bonds.
Water molecules stick to other water molecules because hydrogen bonds form between the hydrogen atoms of one water molecule and the oxygen atoms of other water molecules.

31. WATER’S LIFE-SUPPORTING PROPERTIES
2.11 Hydrogen bonds make liquid water cohesive
Due to hydrogen bonding, water is cohesive and can:
Move from a plant’s roots to its leaves
Cling to your body after turning off the shower.

32. Cohesion-holds molecules of a single substance together.
Ex. Water holding onto water
Surface Tension-the measure of how difficult it is to stretch or break the surface of a liquid.

33. Water and Solutions
Adhesion-force between two particles of different substances
Ex. Water holding onto a straw
Capillary action-causes water to rise of the surface of a liquid when in contact with a solid.

34. 2.12 Water’s hydrogen bonds moderate temperature
2.12 Water’s hydrogen bonds moderate temperature
Water’s ability to store heat
Moderates body temperature and climate
Specific Heat-the amount of heat required to change a substance by one degree in temperature.
High specific heat-requires a high amount of energy to transform between states.
Ex. water

35. It takes a lot of energy to disrupt hydrogen bonds
So water is able to absorb a great deal of heat energy without a large increase in temperature
As water cools
A slight drop in temperature releases a large amount of heat

36. A water molecule takes energy with it when it evaporates
A water molecule takes energy with it when it evaporates
Leading to evaporative cooling
Figure 2.12

37. 2.13 Ice is less dense than liquid water
2.13 Ice is less dense than liquid water
Hydrogen bonds hold molecules in ice farther apart than in liquid water
The hydrogen bonds in ice are more stable than the hydrogen bonds in liquid water.
Figure 2.13
Hydrogen bond
Ice
Hydrogen bonds are stable
Liquid water
Hydrogen bonds constantly break and re-form

38. Ice is therefore less dense than liquid water which causes it to float
Ice is therefore less dense than liquid water which causes it to float
Floating ice protects lakes and oceans from freezing solid
As ice melts, hydrogen bonds are broken.

39. 2.14 Water is the solvent of life
2.14 Water is the solvent of life
Polar or charged solutes dissolve when water molecules surround them, forming aqueous solutions
A solute is  the substance that is dissolved in solution.  
Na+ –
Na+ – +
Cl– + – – + –
Cl– + – + – + – + – –
Ion in solution
Salt crystal
Figure 2.14

40. 2.15 The chemistry of life is sensitive to acidic and basic conditions
Electrolytes-solutions that contain electrically changed particles that conduce an electrical current.

41. A compound that releases H+ ions in solution is an acid
A compound that accepts H+ ions or donates OH- in solution is a base
Acidity is measured on the pH scale
From 0 (most acidic) to 14 (most basic)

42. The pH scale Figure 2.15 pH scale 1 2 3 4 5 6 7 8 9 10 11 12 13 14
The pH scale
pH scale 1 H+ H+ H+
OH– H+ 2
Lemon juice, gastric juice
OH– H+ H+ H+ H+
Increasingly ACIDIC (Higher concentration of H+) 3
Grapefruit juice, soft drink
Acidic solution 4
Tomato juice 5 6
Human urine
OH–
OH–
OH–
NEUTRAL [H+]=[OH–] 7
Pure water Human blood H+ H+
OH–
OH– H+ H+ H+ 8
Neutral solution
Seawater 9 10
Increasingly BASIC (Lower concentration of H+)
Milk of magnesia 11
OH–
Household ammonia
OH– 12
OH– H+
OH–
Household bleach
OH–
OH–
OH– 13 H+
Oven cleaner
Figure 2.15
Basic solution 14

43. The pH of most cells is kept close to 7 (neutral) by buffers
An increase in hydrogen ion concentration means a decrease in pH scale units
Buffers are substances that resist pH change by donating H+ ions when conditions become too basic and accepts H+ ions when conditions become too acidic.  

44. 2.16: Acid precipitation threatens the environment
CONNECTION
2.16: Acid precipitation threatens the environment
Acid precipitation is any precipitation with a pH lower than 5.6.
Acid precipitation is formed when air pollutants from burning fossil fuels
Combine with water vapor in the air to form sulfuric and nitrogen oxide

45. These acids Can kill trees and damage buildings
These acids
Can kill trees and damage buildings
Figure 2.16A
Figure 2.16B

46. How to decrease acid precipitation:
drive more fuel-efficient automobiles.  
decrease our consumption of coal-generated electricity.  
encourage the use of alternative energy resources such as solar, wind, and geothermal energy.  
whenever possible, walk or ride a bicycle instead of driving a car.  

47. CHEMICAL REACTIONS
2.17 Chemical reactions change the composition of matter
In a chemical reaction
Reactants interact, atoms rearrange, and products result
2 H2 O2
2 H2O
Figure 2.17A

48. Characteristics of chemical reactions:
Chemical reactions involve the making and breaking of chemical bonds.  
The atoms of the reactants are exactly the same as the atoms of the products.  
The reactants contain the same number of atoms as the products.  
Although the atoms of a reaction's reactants and products are identical to each other, their molecular formulae differ.  

49. Living cells carry out thousands of chemical reactions
Living cells carry out thousands of chemical reactions
That rearrange matter in significant ways
CH3
CH3
CH3
CH3
CH3 C
CH2
CH3
CH3
CH3 H
H2C H C CH C CH C CH CH CH CH CH C
CH2
H2C C CH C CH C C
CH2 C OH CH CH CH CH CH C CH C CH C
CH2 O2 4H 2
CH2 C CH CH CH CH
H2C C
CH3
CH3
CH3
H2C C
CH3
CH3
Beta-carotene
CH3
CH3
Vitamin A (2 molecules)
Figure 2.17B