2. The Chemical Basis of Life
Chapter 4
The Chemical Basis of Life

3. 4.1 Life requires about 25 chemical elements…
A. Matter
Anything that occupies space and has mass
3 states: solid, liquid, gas

4. 4.1 Elements & Compounds… a. Elements Pure substance,simplest form
Made up of 1 type of atom
Ex: Hydrogen (H), oxygen (O), nitrogen (N)
(~110 elements on Periodic Table)

5. Open your Agenda….
Page 124

7. 4.1 Elements & Compounds… Compound 2 or more elements
Chemically combined in a fixed ratio
Written as formulas
Ex: water – H2O
carbon dioxide – CO2

8. 4.1 Elemental Composition of the Human Body
Chemical Symbol Mass (70Kg person)
O Kg
C Kg
H Kg
N Kg
Ca Kg
P g
K g
Trace elements make up <0.01% of your body

9. Important Elements in Life….
C HOPKINS CaFe Mg NaCl
(What elements are represented here?)

10. The Most Important Elements in Life….
HONC
(What elements are represented here?)

11. 4.2 What are atoms?
Basic building blocks of matter
(A desk, the air, you are made up of atoms!)

13. 4.2 Atoms are made out of 3 basic particles…
Electrons
negatively charged particles that move around the nucleus in orbitals e-

14. 4.2 The other 2 particles are found within the nucleus…
Nucleus – center of the atom
Proton – positively charged particle
Neutron – neutral particle

15. 4.2 Structure of the atom

16. 4.3 Chemical bonds join atoms
Bonds hold atoms together
2 types of bonds:
Covalent
Ionic

17. 4.3 Covalent Bond
A bond formed when atoms SHARE electrons
2 or more atoms held together by covalent bonds form a molecule

19. 4.3 Ionic Bond A bond formed when atoms TRANSFER electrons.
One atom LOSES electrons; another GAINS electrons.
An ION is formed

21. 4.3 Chemical Formulas…
Molecular (Chemical): shows the kind of atoms and the number of each
Structural: shows the arrangement of atoms in a compound (the bonds)

22. Molecular formula of water
H2O

23. Structural formula of water

24. Molecular formula of glucose
C6H12O6

25. Structural formula of glucose

27. 4.3 Chemical Equations Represent a chemical reaction
Ex. 2 H2 + O H2O

28. 4.3 Reactants & Products
Reactants = the chemicals on the LEFT side of the equation 
Products = the chemicals on the RIGHT side of the equation (are made or produced in the reaction)

29. 4.3 Balanced Equations
Number of each atom on the right equals the number on the left.

30. Balanced equations
2 H O H2O

31. 4.3 Balanced Equation Example
H2 + O H2O
is unbalanced
Why?

32. 4.3 Balanced Equations
To BALANCE equations, numbers called COEFFICIENTS are added in front of the compounds.

33. Chemistry of Life Movie Link
Start at 2:30 End at 8:48

35. 4.4 Unique properties of water
Cohesion – molecules of the same kind “stick” to one another
Adhesion – attraction between unlike molecules
Ex: meniscus

36. 4.4 Unique properties of water
Cohesion & Adhesion:
Trees depend on these forces!! Why?
Water evaporates, pulls another water up (cohesion) from leaves down stems into roots!

37. H2O
Adhesion & Cohesion

38. 4.4 Water dissolves other substances
Solutions are formed from a uniform mixture of 2 or more substances
Ex. Dissolving salt into water

39. 4.4 What makes up a solution?
Solvent – substance that dissolves the other and is in greater quantity
Water = universal solvent

40. 4.4 What makes up a solution??
Solute – substance that is dissolved and is present in lesser amounts
Ex. salt

41. 4.4 What makes up a solution?
When water is the solvent it forms an aqueous solution

42. __________________________________________________________________
Note Packet Page 4:
4.4 The pH Scale
It is a measure of the concentration of hydrogen ions in a solution.
It ranges from 0 to 14.
Neutral
__________________________________________________________________
0 Acids Bases 14

43. 4.4 The pH Scale Hydrogen ions H+ (lost an electron) Hydroxide ions
OH- (gained an electron)

44. 4.4 Acids… pH range – less than 7 Examples: HCl (hydrochloric acid)
Vinegar (acetic acid)
Lemon juice (citric acid)

45. 4.4 Acids…
Have more H+ ions than water does.
Have fewer OH- ions

46. 4.4 Bases… pH range–greater than 7 Examples: NaOH (sodium hydroxide)
Ca(OH)2 (calcium hydroxide)
NH3 (ammonia)

47. 4.4 Bases…
Have fewer H+ ions than water does
Have many OH- ions

48. 4.4 Neutral Substances…
pH – equals 7
Example:
Pure water (H2O)

51. 4.4 Buffers… Helps maintain constant pH Accepts or donates H+ ions
Many biological fluids contain buffers!! Why??

52. 4.4 Indicators…
Chemicals that turn different colors in different pH values
Bromothymol Blue, Phenolphthalein, pH paper
DEMO: take notes on page 8 of your observations!

53. Chemistry of Life Movie Link
Start at 2:30 End at 8:48