1. The Chemistry of Life Chapter 2

2. Why should we study chemistry in
Biology?
Life depends on chemistry!

3. Life depends on chemistry!
When you eat food or inhale oxygen, your body uses these materials in chemical reactions that keep you alive.
Just as buildings are made from bricks, steel, glass, and wood, living things are made from chemical compounds.
Wouldn’t you want an architect to understand building materials? Same idea applies to geneticists, ecologists, zoologists, botanists, biologists, and etc.

4. Atoms
The study of chemistry begins with the basic unit of matter…the
History
Greeks were first to try to explain chemical reactions
400 BC: thought all matter composed of:
Fire
Earth
Water
Air
Democritus first used word “atomos”, meaning indivisible
Atom

5. Atoms Atoms are composed of 3 main particles: (subatomic particles)
Protons (+)
Neutrons
Electrons (-)

6. Protons and Neutrons
Strong forces bind protons and neutrons together to form the nucleus, which is at the center of the atom.
Both particles have about the same mass.

7. Electrons
Electrons are negatively charged with about 1/1840 the mass of a proton.
They are in constant motion in the space surrounding the nucleus.

8. Atoms Atoms have equal numbers of electrons and protons.
Because these subatomic particles have equal but opposite charges, atoms are neutral.

10. Elements Elements are the building blocks of all matter.
Elements cannot be decomposed into simpler matter.
Group Number:

11. The Elements 110 known elements 88 occur naturally
The 110 elements form a plethora of compounds, just as 26 letters of the alphabet make a seemingly endless number of words.

12. Atomic Number
Counts the number of
protons
in an atom

13. Atomic Number on the Periodic Table11 Na
Atomic Number
Symbol

14. All atoms of an element have the same number of protons11 Na
11 protons
Sodium

15. Atomic Mass Mass of an atom.
Approximately equal to the number of protons and neutrons
Find number of neutrons by subtracting the number of protons from the mass.

16. Review:
An element's atomic number tells how many protons are in its atoms.
An element's mass number tells how many protons and neutrons are in its atoms.

17. Learning Check 1
State the number of protons for atoms of each of the following:
A. Nitrogen
1) 5 protons 2) 7 protons 3) 14 protons
B. Sulfur
1) 32 protons 2) 16 protons 3) 6 protons
C. Barium
1) 137 protons 2) 81 protons 3) 56 protons
2) 7 protons
2) 16 protons
3) 56 protons

18. The Periodic Table

19. Isotopes What does that mean?
Isotopes are atoms that have the same atomic number but different mass number.
Most elements have two or more isotopes.
Same chemical properties because the electron number does not change.
What does that mean?

20. Isotope symbols X A Z
Mass number
Atomic number

21. B Example How many protons does this have?11 5
How many protons does this have?
How many neutrons does this have?
Is the “5” necessary ?

22. More about isotopes:
Some isotopes have unstable nuclei which break down over time.
They are called radioactive isotopes
Some radiation is harmful.

23. Radiation can also be useful
Radioactive Dating
Tracers with X-rays
Cancer Treatment
Kill bacteria

24. More About Atomic Structure
The center of the atom is called the nucleus.
Electrons live in something called shells.
Shells are areas that surround the center of an atom.
A shell is sometimes called an orbital or energy level.

25. More About Electrons Every shell can hold only so many electrons
The further from the nucleus, the more electrons a shell can hold

26. Valence Electrons The electrons on the outside edge of the atom
This is where the action is- where bonding takes place
Atoms have no more than 8 valence electrons

27. The Octet Rule:
Atoms will combine to form compounds in order to reach eight electrons in their outer energy level. This is very stable!
Atoms with less than 4 electrons tend to lose electrons.
Atoms with more than 4 electrons tend to gain electrons.

28. Compound
Two or more elements chemically combined in specific proportions
Examples:
Water H2O
Salt NaCl
Sugar C6H12O6
Chemical Formulas are used to represent compounds
Two types of compounds:
Ionic
Covalent

29. Ionic Compounds
Form when electrons are transferred from one atom to another.
Ions - Atoms with a net charge due to gaining or losing electrons
Gaining electrons gives an ion a negative charge
Losing electrons gives an ion a positive charge
**If they have to choose, atoms would rather be stable (with a full “octet”) than neutral.

30. How Does This Happen? Some atoms have a few too many electrons
Some atoms only need a few electrons

31. What do you do if you are a sodium (Na) atom with one extra electron?
Go look for an atom that wants it!

32. Ionic Bonding
Negative ions and positive ions are held together by ionic bond.

33. Ionic compounds form between metals and nonmetals

34. What If No One Will Give Up An Electron?
Atoms with less than 8 valence electrons can move close to each other and share their electrons
The electrons spend their time around both atoms.
And they lived happily ever after!

35. Covalent Bonds
Formed when a pair of electrons is shared between two atoms.
Sometimes the atoms share two pairs of electrons and form a double bond, or three pairs of electrons to form a triple bond.
Structures formed by
covalent bonds are
molecules.

36. Covalent compounds form between 2 nonmetals

37. Van der Waals Forces
There are small attractive forces between all atoms
Help to hold molecules to each other
Ex: Gecko

38. Let’s summarize what we know!
Why do compounds form?
Atoms are trying to get 8 valence electrons
How do compounds form?
By ionic (e- transfer) or covalent (e- sharing) bonding
How can you tell if a compound is ionic or covalent?
By the types of elements in the compound (ionic = M + NM covalent = NM + NM)

39. Learning Check 2:
Indicate whether a bond between the following would be 1) Ionic 2) covalent
___ A. sodium and oxygen
___ B. nitrogen and oxygen
___ C. phosphorus and chlorine
___ D. calcium and sulfur
___ E. chlorine and bromine

40. 2-2 Water is a Polar Molecule
Polar: Molecule in which electrons are shared unevenly between atoms, causing each end of the molecule to have a slight charge
Negative end
Positive end

41. This causes water to be attracted to other polar or charged particles
Water is attracted to ions
Water is attracted to itself, forming hydrogen bonds

42. Hydrogen Bonds In Water Are Responsible For:
Adhesion
Attraction between molecules of different substances
Graduated cylinder
Cohesion
Attraction between molecules of the same substance
Drops of water on a penny
Ex: Surface Tension
Jesus Lizard

43. Types of Chemical Substances
Compounds and Elements are called pure substances.
Most matter is neither of these.

44. Mixtures
Mixtures are combinations of substances held together by physical forces, not chemical bonds.
Each substance keeps its own properties

45. Mixtures may be either:
Solutions
Colloids
Suspensions

46. Solutions Have small particles
Are transparent (not the same as colorless)
Do not separate
Water solutions are very common in biological systems
Examples: salt water, kool-aid, air, brass, vinegar

47. Colloids Have medium size particles Do not separate
Examples: fog, whipped cream, milk, cheese, mayonnaise

48. Suspensions Have very large particles
Settle out (separates into layers)
Examples: blood platelets, muddy water, calamine lotion, oil & water, Italian salad dressing

49. pH Scale Measures concentration of hydrogen ions in a solution
Ranges from 0 to 14
7 is neutral
0-7 have more hydrogen ions (H+) and are acidic
7-14 have more hydroxide ions (OH-) and are basic

50. Acids, Bases, and pH Water molecules form ions
H2O H OH-
Water hydrogen ion hydroxide ion
Very few ions are formed in pure water, but there are equal numbers of hydrogen and hydroxide ions
Water is neutral!

51. pH of common substances

52. pH and Homeostasis
Maintaining a pH between 6.5 and 7.5 is important in cells
Dissolved compounds called buffers control pH
Proteins
Phosphates
Hydrogen carbonate

53. Chemical Reactions
When one set of chemicals changes into another set of chemicals, a chemical reaction occurs
Bonds are either broken or formed (or both!)

54. Chemical Equations 2H2O Represent a reaction
Give the types and amounts of substances that react and form
Reactants Products
2H2 + O2
“yields”
“yields”
2H2O

55. Evidence of a Chemical Reaction
Formation of a precipitate (a solid substance separated from a liquid)
Gas is evolved (seen by bubbles forming in a liquid)
Change in heat or light energy

56. Organic Compounds

58. Organic Compounds Make up most of living organisms
Contain bonds between two or more carbon atoms
C can easily bond with up to 4 other elements
4 valence electrons = 4 covalent bonds

59. Organic Compounds
Carbon atom is versatile, can be “backbone” of long chains or rings
Organic molecules can be extremely large and complex; these are called macromolecules

60. Organic Compounds Four main types of organic macromolecules:
Carbohydrates
Lipids
Proteins
Nucleic Acids

61. Carbohydrates Made of C, H, & O Main energy source for living things
Breakdown of sugars supplies immediate energy for cell activities
Extra sugar is stored as complex carbs called starches

62. Carbohydrates Single sugar molecules are called monosaccharides
Examples:
glucose – in many plant and animal tissues, most common monosaccharide
fructose – in many fruits
galactose – component of milk

63. Carbohydrates
Large molecules of many monosaccharide are polysaccharides
Examples:
glycogen – animals use to store excess sugar
plant starch – plants use to store excess sugar
cellulose – fibers that give plants their rigidity & strength

65. Lipids Store more energy than CHOs because the chains are longer
Ex: Fats, oils, waxes
Won’t dissolve in water

66. Lipids
Important parts of biological membranes and waterproof coverings
Steroids are lipids that act as chemical messengers

67. Lipids Many lipids are made from a glycerol combined with fatty acids
If all carbons have single bonds, lipid is saturated
Ex: butter, lard, animal fat (usually solid at room temperature)
If any carbons have double or triple bonds, lipid is unsaturated
Ex: vegetable oil, fish oil, peanut oil (usually liquid at room temperature)

69. Proteins Contain C, H, O, plus nitrogen
Formed from amino acids joined together
More than 20 amino acids can be joined in any order or number to make countless proteins (think of how many words can be made from 26 letters!)

70. Proteins
Chains are folded and twisted giving each protein a unique shape
Van der Waals forces and hydrogen bonds help maintain protein’s shape
Shape of protein is important to its function!

71. Proteins Provide structure Aid chemical activities in your body
Ex: Collagen- makes up your skin, muscles & bones
Aid chemical activities in your body
Ex: Enzymes- work to speed up rxns in your body
Transport substances into or out of cells
Help fight diseases

73. Nucleic Acids Contain C, H, O, N plus phosphorus
Formed by bonding of individual units called nucleotides
Nucleic Acid
nucleotide

74. Nucleic Acids Store and transmit hereditary information
Ex: DNA (deoxyribonucleic acid)
RNA (ribonucleic acid)