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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
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.
Milkweed contains cardiac glycosides that are poisonous to humans and livestock, as well as alkaloids.
Plants containing cardiac steroids have been used as poisons and heart drugs at least since 1500 B.C.
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 you Change the Element !
• An atom has protons and neutrons located in a central nucleus
Figure 2.4A A. Helium atom
2
2
2
Protons
Neutrons
Electrons
Nucleus
• The nucleus is surrounded by electrons, which orbit so fast they form “clouds” around the nucleus
SODIUM
ATOM11 p+
11 e-
electron transfer
CHLORINEATOM17 p+
17 e-
SODIUMION11 p+
10 e-
CHLORINEION17 p+
18 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?
– 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
• In a water molecule, oxygen’s 8P has a stronger pull on the shared electrons than hydrogen’s 1P
Figure 2.9
(–)
O
(–)
(+)(+)
H H
8 protons
1 proton 1 proton
Electrons drawn to this side
• water molecules are attracted to the oppositely charged regions on nearby molecules– This attraction forms
weak bonds called hydrogen bonds
Water’s polarity leads to hydrogen bonding and unusual properties
\
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?
Adhesion + cohesion
Evaporation “pulls”
water into the roots
molecule by molecule
TRANSPIRATION IN PLANTS
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)
20
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)
21
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
• 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
The chemistry of life is sensitive to acidic and basic conditions
Ocean pH + CO2As 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)