The Chemistry of Life Chapter 2 - PowerPoint PPT Presentation

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Title: The Chemistry of Life Chapter 2


1
The Chemistry of LifeChapter 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.
  • Wouldnt 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 matterthe
  • 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.

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10
Elements
  • Elements are the building blocks of all matter.
  • Elements cannot be decomposed into simpler matter.

Group Number 1 2
3 4 5 6 7 8
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 Table
14
All atoms of an element have the same number of
protons
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
  • 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
21
Example
  • 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
Energy Level (Shell) Maximum Number of Electrons Max number of Valence Electrons
1 2 2
2 8 8
3 18 8
4 32 8
5 50 8
6 72 8
7 98 8
28
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.

29
Compound
  • Two or more elements chemically combined in
    specific proportions
  • Examples
  • Water H2O
  • Salt NaCl
  • Sugar C6H12O6
  • Two types of compounds
  • Ionic
  • Covalent

30
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.

31
How Does This Happen?
Some atoms have a few too many electrons
Some atoms only need a few electrons
32
What do you do if you are a sodium (Na) atom
with one extra electron?
  • Go look for an atom that wants it!

33
Ionic Bonding
  • Negative ions and positive ions are held together
    by ionic bond.

34
  • Ionic compounds form between metals and nonmetals

35
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!

36
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.

37
  • Covalent compounds form between 2 nonmetals

38
Van der Waals Forces
  • There are small attractive forces between all
    atoms
  • Help to hold molecules to each other
  • Ex Gecko

39
Why do compounds form?
Lets summarize what we know!
  • 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 M covalent M NM)

40
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
41
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
42
  • 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

43
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

44
Types of Chemical Substances
  • Compounds and Elements are called pure
    substances.
  • Most matter is neither of these.

45
Mixtures
  • Mixtures are combinations of substances held
    together by physical forces, not chemical bonds.
  • Each substance keeps its own properties

46
Mixtures may be either
  • Solutions
  • Colloids
  • Suspensions

47
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

48
Colloids
  • Have medium size particles
  • Do not separate
  • Examples fog, whipped cream, milk, cheese,
    mayonnaise

49
Suspensions
  • Have very large particles
  • Settle out (separates into layers)
  • Examples blood platelets, muddy water, calamine
    lotion, oil water, Italian salad dressing

50
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

51
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!

52
pH of common substances
53
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

54
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!)

55
Chemical Equations
  • Represent a reaction
  • Give the types and amounts of substances that
    react and form
  • Reactants Products
  • 2H2 O2

yields
yields
2H2O
56
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

57
Organic Compounds
58
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59
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
60
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

61
Organic Compounds
  • Four main types of organic macromolecules
  • Carbohydrates
  • Lipids
  • Proteins
  • Nucleic Acids

62
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

63
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

64
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

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Lipids
  • Store more energy than CHOs because the chains
    are longer
  • Ex Fats, oils, waxes
  • Wont dissolve in water

67
Lipids
  • Important parts of biological membranes and
    waterproof coverings
  • Steroids are lipids that act as chemical
    messengers

68
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)

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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!)

71
Proteins
  • Chains are folded and twisted giving each protein
    a unique shape
  • Van der Waals forces and hydrogen bonds help
    maintain proteins shape
  • Shape of protein is important to its function!

72
Proteins
  • Provide structure
  • 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

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Nucleic Acids
  • Contain C, H, O, N plus phosphorus
  • Formed by bonding of individual units called
    nucleotides

Nucleic Acid
nucleotide
75
Nucleic Acids
  • Store and transmit hereditary information
  • Ex DNA (deoxyribonucleic acid)
  • RNA (ribonucleic acid)

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