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.

4. It all begins with… Atoms – the smallest unit of matter 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

5. Atoms are composed of 3 main particles: (subatomic particles)
Protons (+)
Neutrons (0)
Electrons (-)

6. Protons and Neutrons
Nucleus – Center of atom that contains protons and neutrons.
Both particles have about the same mass.

7. Electrons Electrons are about 1/1840 the mass of a proton.
They are in constant motion in the space surrounding the nucleus.
Electron cloud model

8. Atoms have equal numbers of electrons and protons.
This makes an atom neutral

10. The Elements 116 known elements 92 occur naturally
Only 25 are important to living organisms!

11. Elements Atomic number – number of protons
Atomic mass – number of protons and neutrons. (amu)
Atomic symbol – letters naming the element

12. 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

13. The Periodic Table

14. More Electrons Electrons reside in something called shells.
Shells are areas that surround the center of an atom. (aka. orbitals and energy levels)

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

16. Electrons
Valence electrons - the electrons on the outside shell of the atom
This is where bonding takes place
Atoms have no more than 8 valence electrons

17. Maximum Number of Electrons Max number of Valence Electrons
Energy Level (Shell)
Maximum Number of Electrons
Max number of Valence Electrons 1 2 8 3 18 4 32 5 50 6 72 7 98

18. 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.

19. Review How many protons, electrons, and neutrons are in…
Boron
Chlorine
Sodium
How many valence electrons does each of these elements have?
What is the chemical formula for water?

20. 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

21. Ionic Compounds
Form when electrons are transferred from one atom to another. (stealing)
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.

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

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

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

25. Ionic compounds form between metals and nonmetals

26. What If No One Will Give Up An Electron?
Covalent Bonds -
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!

27. Covalent Bonds
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.

28. Covalent compounds form between 2 nonmetals

29. 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 = NM + M covalent = NM + NM)

30. 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

31. Dot structures – Bonding

32. How many bonds are formed?
Carbon
Nitrogen
Oxygen
Hydrogen

33. Make Some Molecules Ammonia – NH3 Methane – CH4 Carbon Dioxide – CO2
Propane – C3H8
Urea – H4N2CO
Glucose – C6H12O6

34. 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!)

35. Our bodies use nutrients through chemical reactions!
Reactants – molecules/elements prior to reaction
Products – molecule/elements produced as a result of the reaction
C6H12O6 + O CO2 + H2O
Energy

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

37. Law of conservation of mass
States that matter is not created or destroyed during a chemical reaction
Even though the matter may change from one form to another, the same number of atoms exists before and after the change takes place!
Mass of
Reactants
Mass of
Products

38. Lets Make water!
2 H2 O2
2 H2O

39. Iron + Oxygen  Ironoxide

40. TAKE A LOOK AT THE NUMBERS
Each made of TWO oxygen atoms Fe Fe O2
Fe2O3
Fe2O3 Fe Fe O2 O2
What about the PRODUCT?
How many Oxygen molecules?
How many Iron molecules?
PRODUCT
REACTANTS

41. How do we write it?
Fe + O2  Fe2O3 N2 + H2  NH3 KClO3  KCl + O2

42. CO2 + H2O  C6H12O6 + O2 C8H18 + O2  CO2 + H2O NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2

43. Organic Compounds

44. Organic Compounds Make up living organisms Contain the element carbon
4 valence electrons = 4 covalent bonds

45. Organic Compounds
The carbon atom is versatile, it can form large, complex compounds called macromolecules
Monomer –
Polymer –

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

47. Carbohydrates Made of C, H, & O H to O ratio is always 2:1
Monomer – monosaccharide
Ex. Glucose, sucrose
Polymer – polysaccharide
Ex. Starch, cellulose, fiber
Main energy source for living things

48. Carbohydrates Monosaccharide Examples:
glucose – in many plant and animal tissues, most common monosaccharide
fructose – in many fruits
galactose – component of milk

49. Carbohydrates 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

50. Carb Sizes

51. Making bigger molecules
Dehydration Synthesis – is a process that connects two large molecules
By removing a water molecule

52. Breaking down big molecules
Hydrolysis – is a process that separates two large molecules
By adding a water molecule

54. Lipids Store a lot of energy Monomers – Glycerol & Fatty acids
Polymers – Fats & Oils

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

56. Lipids 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)

57. Fats vs. Oils

59. Proteins Contain C, H, O, and N Monomers – amino acids
25 different kinds (R groups)
Polymers – proteins

60. Proteins Shape of protein is important to its function!
Chains of AA’s are folded and twisted giving each protein a unique shape
Ionic charges and hydrogen bonds help maintain protein’s shape
Shape of protein is important to its function!

61. 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

62. Dehydration synthesis!

64. Nucleic Acids Contain C, H, O, N plus phosphorus (P)
Monomer – Nucleotide
5 of them (A, T, C, G, U)
Made of sugar, phosphate, and base
Polymer – Nucleic Acid
Ex. DNA, RNA

65. Nucleotide
Nucleic Acids

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