Environmental Science Geology 1401410 Instructor: Don Thieme

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Environmental ScienceGeology 1401-410Instructor
Don Thieme

• 5th Lecture Chemical Reactions, Organic
  Compounds, and Biogeochemical Cycles

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An atom is the smallest particle that exhibits
the characteristics of an element. Atoms are
composed of positively charged protons,
negatively charged electrons, and electrically
neutral neutrons.
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Charge

• an atom is electrically neutral when it has the
  same number of protons and electrons
• positive charge occurs when an atom loses one or
  more electron
• negative charge occurs when an atom gains one or
  more electron
• charged atoms are called ions

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Electronegativity

• the ability of an atom to attract valence
  electrons toward its nucleus
• increases toward the upper right of the periodic
  table because
• atomic mass is highest within period
• distance of valence electrons from nucleus is
  lowest within group

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Important Elements
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Chemical Bonds

• hold molecules together
• ionic
• the most stable
• cation charge of metal atoms exactly balanced by
  anion charge of nonmetal atoms (NaCl combines Na
  and Cl-)
• covalent
• join two or more nonmetal ions

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Molecules held together by covalent bonds are
common constituents of the Earth's atmosphere
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Names of Ionic Compounds

• name of metal element comes first
• followed by nometal element's name
• "ide" for ionic bond
• potassium chloride (KCl)
• aluminum oxide (Al2O3)
• calcium fluoride (CaF2)
• charge may be indicated two ways
• ferrous chloride - Fe(II)Cl
• ferric chloride - Fe(III)Cl

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Chemical Reactions

• Chemical bonds are stretched, broken, and
  reformed by reactions between atoms and compounds
• Energy is required for a chemical reaction to
  place. This is referred to as the activation
  energy.
• Energy is released when bonds are broken,
  typically as heat.

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Concentration and Activity

• whether or not a reaction will occur depends on
  the concentration of the two reactants as well as
  their chemical properties
• the effects of concentration for various
  molecules are referred to as their activity (a)
• a the number of moles per cubic centimeter
  (mol cm-3)

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Combustion of Methane

• CH4 2 O2 - - - gt CO2 2 H2O
• (reactants) (products)
• balanced equation - the same number of each
  kind of atom appears on both sides

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Oxidation of Iron
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3
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___ Fe ___ O2 - - - gt ___ Fe2O3
Each iron (Fe) atom gives up three electrons to
form the bond.
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Photosynthesis
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___ H2O __ CO2 light energy - - - gt
__ O2
__ C6H12O6 __ H2O
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(glucose)
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Solar Energy

• Sun reaches 15 million Kelvin
• fusion of H to He
• emits full spectrum of electromagnetic energy
• from 0.01 nm (gamma rays) to 10 cm (radio waves)

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Electromagnetic spectrum

• solar energy in and near the wavelengths of
  visible light drives photosynthesis and many
  other chemical reactions on Earth

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Photosynthesis is actually a series
of light-dependent reactions occurring within
the cells of plants. Chloroplasts are
the organelles responsible. The chlorophyll
molecule acts as catalyst but the reactions
occur in many other molecules. Glucose and
other sugars are "high-energy intermediaries"
that are broken down by plants.
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Cellular Respiration
C6H12O6 6 O2 - - - gt 6 H2O 6 C O2
energy
Energy is released by respiration, whereas in
photosynthesis energy is captured.
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Organic Compounds

• large molecules built around atoms of carbon (C)
• chains, rings, or some combination of both
• H, O, N, P, and K are other elements that
  commonly occur in organic molecules

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Organic Compounds
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Polar and Nonpolar Bonds

• Covalent bonds are nonpolar if shared electrons
  fit midway between the two nuclei - O2, N2, Cl2
• When one nucleus has greater charge, the electron
  will move closer to the more electronegative atom
• some polar molecules - HF, H20, CH3Cl

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Polar Organic Compounds

• many of the properties of organic compounds are
  the result of the polarity of covalent chemical
  bonds within their molecules
• polar molecules have higher melting and boiling
  points
• CH3Cl methyl chloride
• CH3OH methyl alcohol (methanol)

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CH3OH
ball and stick
H
H
C - O
H -
space filling
H
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Hydrocarbons (lipids)

• built upon a chain of carbon atoms

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IUPAC

• International Union of Pure and Applied Chemistry
• rules for naming organic compounds
• for hydrocarbons attach the suffix -ane to a
  prefix denoting the number of carbons (n) in the
  compound
• methane(1), ethane(2), propane(3), butane(4),
  pentane(5), hexane(6), heptane(7), octane(8),
  nonane(9), decane(10)

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Carbohydrates

• rings or chains
• of C atoms

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Proteins

• chains of amino acids.
• Nitrogen (N) is an important component
• of proteins

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Nucleic Acids

• chains of nucleotides linked by
• phosphate-sugar bonds

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Carbon Cycle
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Primary Production

• photosynthesizing organisms, particularly plants,
  are the primary producers in an ecosystem
• organisms that do not photosynthesize are
  consumers
• consumers break down the high-energy
  intermediaries, use up oxygen, and emit carbon
  dioxide to the atmosphere.

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CARBON CYCLE begins with photo- synthetic
organisms taking up CO2 high-energy
intermediates are more rapidly recycled
than hydrocarbon (CH2 and CH3)
molecules carbonate (CO3) and bicarbonate
(HCO3) molecules
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Chloroplasts are specialized organelles for Photos
ynthesis
Mitochondria are specialized organelles for
Aerobic Respiration, regulated by enzymes.
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Nitrogen

• 78 of the lower atmosphere
• NO nitric oxide
• N2O nitrous oxide
• NO2 nitrogen dioxide
• NO3 nitrate
• HNO3 nitric acid
• NH3 ammonia
• NH4 ammonium

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Nitrogen Cycle

• Plants cannot use N2. They use nitrogen "fixed"
  by bacteria
• cyanobacteria (bluegreen algae) and bacteria that
  live on legume (bean) roots combine gaseous N2
  and H2O to make ammonia (NH3)
• "Nitrification" (NH3 to NO3)
• 1. Nitrosomos oxidizes NH4 to NO2
• 2. Nitrobacter oxidizes NO2 to NO3
• rate for 2 is more rapid than 1, so NO2 is found
  only in trace amounts

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Bacteria that cycle Nitrogen

• nitrogen-fixing bacteria combine combine gaseous
  N2 and H2O to make ammonia (NH3)
• nitrifying bacteria oxidize ammonia to make
  nitrates
• denitrifying bacteria break down nitrate (NO3)
  into N2 and nitrous oxide (N2O)

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N in Organic Molecules

• N combines with C (H, O, etc....) to form many
  organic molecules
• amino acids
• peptides
• proteins
• CH3CH2NH2 methyl ethyl amine
• C6H5NH2 aniline

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Liebig's Law

• first stated by the botanist Justus Liebig in
  1840.
• the growth of a plant is dependent on the amount
  of foodstuff which is presented to it in minimum
  quantity.
• Liebig's "law of the minimum"

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Limiting Nutrients

• the nutrient "presented in minimum quantity"
• the "limiting" nutrient for primary production in
  an ecosystem
• typically is P on land and in freshwater aquatic
  system
• may be N, particularly in coastal ecosystems

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Phosphorus Cycle

• P is not available in the atmosphere
• P is stored in mineral form in marine sedimentary
  rocks and some igneous rocks
• P is usually transported in water
• P is readily metabolized by organisms
• P is returned to mineral compounds by soil
  weathering

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Phosphorus

• P is very often the "limiting" nutrient for
  primary production
• abundant P may initiate a "bloom" in algae and
  hydric plants, a form of pollution because it
  uses up all available oxygen

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Phosphate

• PO4 is phosphate ion.
• Some phosphate minerals
• Ca5(PO4)3(F,Cl,OH) Apatite
• Ca5(PO4)3OH Hydroxyapatite
• Ca5(PO4)3Cl Chlorapatite
• Ca5(PO4)3Cl Fluorapatite

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Phosphate

• Phosphate fertilizers are made by treating
  calcium phosphate (CaPO4) with sulfuric acid
  (H2SO4) to make superphosphate Ca(H2PO4)2
• Fertilizer phosphate increases the rate of the
  phosphorous cycle because it is more reactive and
  also simply increases the abundance of P in
  terrestrial systems.

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Sulfur

• reactive nonmetal
• rare (0.06 ) in Earth's crust
• brittle yellow solid precipitated by hot springs
  (hydrothermal)
• two thirds of the sulfur in the atmosphere comes
  from the eruption of volcanoes

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Sulfur Compounds

• H2S hydrogen sulfide
• FeS2 iron disulfide (pyrite)
• CaSO4 calcium sulfate (gypsum)
• SO2 sulfur dioxide
• SO3 sulfite ion
• SO4 sulfate ion

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Dimethyl Sulfide (DMS)

• CH3CH3S2
• produced by ocean plankton, tiny single-celled
  organisms
• oxidized to SO2 and then SO4
• nuclei for clouds (sulfate aerosols)
• may cool the Earth ("feedback" mechanism for
  global climate change)

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London's "killing fog"

• winter of 1952
• warm air descended and trapped cold air near
  ground
• high sulfur content due to buring of high sulfur
  coal
• droplets of sulfuric acid
• SO3 H2O - - - gt H2SO4

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Acid Rain

• northeastern United States (Adirondack mountains)
  are downwind of coal-fired power plants (Ohio
  Valley)
• sulfate aerosols combine with water vapor to form
  sulfuric acid

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Hydrological Cycle

• The hydrologic cycle is a summary of the
  circulation of Earths water supply
• Processes involved in the hydrologic cycle
• Precipitation
• Evaporation
• Infiltration
• Runoff
• Transpiration

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P I ET ?SM ?GWS RO where P
precipitation I infiltration ET
evapotranspiration ?SM change in soil
moisture ?GWS groundwater storage RO
runoff to streams and the oceans
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Reservoirs in the Cycle
The worlds oceans contain over 97 of its
water. Evaporation exceeds precip over
oceans. Precip exceeds evaporation over
land. Balance is allocated to streamflow.