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. 

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. 

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Periodic Table of the Elements

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

Common Elements in Organic Molecules

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?

Water Molecule =

Atoms sharing electrons

– 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)

Ice is less dense water• So, ice floats and so fish can

survive winter under lake ice.

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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)

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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

The pH 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)

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The wavelengths of visiblelight drive photosynthesis.

The Electromagnetic Spectrum

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Photosynthesis=

CO2 + H20

C6H12O6 + H2O