Chemistry Topics for Us
•
•
•
•
•
•
Plant + animal chemical defenses
Atomic structures: Protons, Neutrons, Electrons
Special properties of water
pH: acids + bases
Light + Energy
Organic Chemistry: Carbohydrates, Proteins,
Lipids + Nucleic Acids
Milkweed contains cardiac glycosides
that are poisonous to humans and
livestock, as well as alkaloids.
The glycoside in milkweed is also a chemical defense for monarch
butterflies. Caterpillars eat the milkweed plant and store the poisons
and make the caterpillar's flesh distasteful to most predators.
Captive bluejays fed
monarchs with
cardenolides throw up
after eating the
monarchs.
Plants containing cardiac steroids have been used as poisons and
heart drugs at least since 1500 B.C.
Periodic Table of the Elements
5
ELEMENT = Its all about the Protons!
= a substance that can’t be chemically
changed into another substance
H=hydrogen, C= carbon, O=oxygen, Au=gold
ELEMENT = # of Protons in an atom
H = 1, He = 2, C = 6, O = 8, Au = 79
ELEMENT = Atomic # = # of Protons
So, if you: Change # Protons in an atom
• An atom has protons and neutrons located in a
central nucleus
• The nucleus is surrounded by electrons, which
orbit so fast they form “clouds” around the
nucleus
2
Protons
Nucleus
Figure 2.4A
2
Neutrons
2
Electrons
A. Helium atom
Common Elements in Organic Molecules
electron transfer
SODI
UM
ATOM
11 p+11 e
SODIUM
ION+
11 p 10 e
CHLORINE
ATOM
17 p+17 e
CHLORINE
ION+
17 p18 e
The Amazing Water Molecule
• Life began in water
• All living things
depend on water
• Water is a simple
molecule, but
without it,
Earth may not be
inhabitable …but
why?
Water Molecule =
Atoms sharing electrons
• In a water molecule, oxygen’s 8P has a stronger
pull on the shared electrons than hydrogen’s 1P
– So, the oxygen end of
the molecule slightly
negatively charged
– The hydrogen end of
the molecule is slightly
positively charged
– Water becomes a
“POLAR” molecule
(–)
Electrons
drawn to
this side
(–)
8 protons
O
H
1 proton
(+)
H
1 proton
(+)
Figure 2.9
Water’s polarity leads to hydrogen
bonding and unusual properties
• water molecules are
attracted to the
oppositely charged
regions on nearby
molecules
– This attraction forms
weak bonds called
hydrogen bonds
\
H-bonds =Water is a versatile solvent
• Reason why things
dissolve in water
– Note: only polar
molecules dissolve
in water
– What substances
don’t dissolve in
water?
Evaporation
“pulls”
water into
the roots
molecule by
molecule
TRANSPIRATION IN
PLANTS
Adhesion
+ cohesion
Molecule by molecule water
enters the roots
Water and it’s Hydrogen Bonds
• Xylem cells allow
plants to draw
water from soil
without energy
(adhesion +
cohesion)
Xylem Plant
Vascular Cells
High Specific Heat
• Reason why rivers,
lakes and oceans
stay relatively cool
– it takes a lot of
energy to warm up
water
– energy is absorbed
by hydrogen bonds
• This, in turn, keeps
our planet from
overheating quickly.
Evaporative Cooling
• Reason why sweating
cools you off so
effectively –
• High heat of
vaporization (takes
lots of energy to
evaporate water)
Ice is less dense water
• So, ice floats and so fish can
survive winter under lake ice.
Water: A Unique Compound
•
•
•
•
60 - 70 % of the weight of living organisms
liquid where all of life's chemical reactions occur
Good electrical conductor
Highest surface tension of any common, natural
liquid = adhesion + cohesion properties
• Expands when it crystallizes, unlike most
substances (ice has greater volume than water)
• High specific heat (water holds a lot of heat
energy)
• High heat of vaporization (takes lots of energy to
evaporate water)
20
Acids and Bases
• Acids are compounds that readily release
hydrogen ions (H+) in water.
• Bases are substances that readily take up
hydrogen ions (H+) and release
hydroxide ions (OH-) in solution.
• pH scale = Strength measured by
concentration of H+ (protons) in water
• 0-14 scale
21
The pH
Scale
The chemistry of life is sensitive to
acidic and basic conditions
• A compound that releases H+ ions in solution is
an acid, and one that accepts H+ ions in solution
is a base
• Acidity is measured on the pH scale:
– 0-7 is acidic
– 8-14 is basic
– Pure water and solutions that are neither basic nor
acidic are neutral, with a pH of 7
Ocean pH + CO2
As carbon dioxide
levels go up, pH
levels go down.
Acidity depends on
the presence of
hydrogen ions (the
H in pH) and more
hydrogen ions
mean, a lower pH.
Expose oceans to
more CO2 it will
produce carbonic
acid, lowering pH
on a planetary
scale.
Acid Rain
• When water vapor in the
atmosphere mixes with
acidic air borne particles
(NO2 or SO2) it can kill
leaves, trees, fish, etc.
H2O + SO2  H2SO4
(sulfuric acid)
H2O + NOx  H2NOx
(nitric acid)
The Electromagnetic
Spectrum
The wavelengths of visible
light drive photosynthesis.
26
Photosynthesis
=
CO2 + H20
C6H12O6 + H2O
27