Chapter 2 - Protecting the Ozone Layer Protecting Ozone:...

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Unformatted text preview: Protecting the Ozone Layer Protecting Ozone: What and Where? Ozone: Ozone: What and Where? Ozone: Allotrope – two or more forms of the same Allotrope element that have different chemical properties. properties. Ozone is formed by rearranging oxygen (O2) O2 + energy → 2 O3 O2 Odorless Condenses at -183°C Light blue liquid Reactive O3 Sharp Odor Condenses at -112°C Dark blue liquid Very reactive Atomic Structure & the Periodic Table Atomic Particle Proton Neutron Electron Sym bol p n eRelative M ass 1 1 1/2000 Relative Charge + 1 0 -1 Location Nucleus Nucleus Outside Nucleus Rule: In an neutral atom # of p = # of e-, but Rule: but the # of n may vary the Atomic Structure & the Periodic Table Atomic Isotopes = atoms of the same element that have different mass numbers have How do isotopes differ from one another? Some isotopes are radioactive Some Isotopes behave the same in chemical reactions Isotopes same number of protons and electrons same Isotopes have different numbers of neutrons and Isotopes different overall mass different Isotope Nam e Hydrogen – 1 Hydrogen – 2 Hydrogen – 3 #of protons 1 1 1 #of electrons 1 1 1 #of neutrons 0 1 2 M (p +n) ass 1 2 3 Atomic Structure & the Periodic Table Atomic Isotopes exist in different naturally occurring abundances abundances Isotope of silicon Si-28 Si-29 Si-30 Isotope of Carbon C-12 C-13 C-14 Abundance 92.23% 4.67% 3.10% Abundance 98.9% 1.11% 1 x 10-12 % Periodic Table vs. Isotope Symbol Periodic Periodic Table Format 79 Au Gold 196.9665 Periodic Table vs. Isotope Symbol Periodic Periodic Table Format 79 Au Gold 196.9665 ← Atom Num – num of protons (and electrons) ic ber ber Periodic Table vs. Isotope Symbol Periodic Periodic Table Format 79 Au Gold 196.9665 ← Atom Num – num of protons (and electrons) ic ber ber ← Elem ental Sym bol ← Nam e Periodic Table vs. Isotope Symbol Periodic Periodic Table Format 79 Au Gold 196.9665 ← Atom Num – num of protons (and electrons) ic ber ber ← Elem ental Sym bol ← Nam e ← Atom m – average m based on relative ic ass ass abundances of isotopes Periodic Table vs. Isotope Symbol Periodic Isotope Symbol A Z X A = Atomic mass number: # of p + # of n in this Atomic atom NOT an average of all isotopes atom Z = Atomic number: # of p in the atom (same as Atomic in periodic table) in X = Elemental Symbol (same as in periodic table) Periodic Table vs. Isotope Symbol Periodic Isotope symbol Ways to write the chemical or isotope symbol: Alone if we don’t care what isotope it is: Mg 24 With the mass number to indicate the isotope: 24Mg With With atomic and mass numbers to be complete: With 24 24 Mg 12 Can also write Magnesium-24 or Mg-24) Isotope Symbols Isotope Identity 33 mass # of protons # of electrons # of neutrons S 113 19 119 60 17 50 27 19 64 20 Isotope Symbols Isotope Identity 33 mass 33 113 39 119 60 36 # of protons 16 49 19 50 27 17 # of electrons 16 49 19 50 27 17 # of neutrons 17 64 20 69 33 19 S In 113 39 K 119 Sn 60 Co Cl 36 Atomic Structure & the Periodic Table Atomic Electron Shells or Electron Levels Electrons are located in specific shells around the Electrons nucleus nucleus Each shell is associated with a particular energy Each level level Each shell has a maximum number of electrons it Each can hold can Shell 1: 2 eShell 2: 8 eShell 3: 8 e- Atomic Structure & the Periodic Table Atomic Element H He Li N S Atomic # Total # of electrons # o f e - in Shell 1 (2 max) # of e- in Shell 2 (8 max) # o f e- i n Shell 3 (8 max) Atomic Structure & the Periodic Table Atomic Element H He Li N S Atomic # Total # of electrons 1 2 3 7 16 1 2 3 7 16 # o f e - in Shell 1 (2 max) 1 2 2 2 2 # of e- in Shell 2 (8 max) 0 0 1 5 8 # o f e- i n Shell 3 (8 max) 0 0 0 0 6 Valence Shell – the outermost shell containing electrons (called valence shell electrons) Remember the gummy? gummy? 2C6H22O11 + 18KClO2 → 18KCl + 12CO2 + 22H2O + energy Atomic Structure & the Periodic Table Atomic Element H He Li N S Number of the valence shell (Ex. Shell 2) Row of the periodic table in which the element is found. Atomic Structure & the Periodic Table Atomic Element H He Li N S Number of the valence shell (Ex. Shell 2) 1 1 2 2 3 Row of the periodic table in which the element is found. 1 1 2 2 3 Atomic Structure & the Periodic Table Atomic Element H He Li N S Number of valence electrons Column of the periodic table in which the element is found. (Ex. 4A) Atomic Structure & the Periodic Table Atomic Element H He Li N S Number of valence electrons 1 2 1 5 6 Column of the periodic table in which the element is found. (Ex. 4A) 1 8* 1 5 6 Molecules and Models Molecules Octet Rule every atom would like to have its valence shell full that is 8 electrons or 2 for H and He this can be on its own (such as column 8A this elements) or by sharing electrons through sharing bonding with other atoms. bonding two electrons shared between two atoms Covalent Bond Molecules and Models Molecules Lewis Dot Structure: Lewis diagram of a molecule showing bonds (1 bond = 2 diagram shared electrons) and lone (unbonded) electrons, usually written in pairs. usually Single bond: Double bond: Double Triple bond: Triple 2 electrons shared electrons 4 electrons shared electrons 6 electrons shared Molecules and Models Molecules Drawing Lewis Dot Structures (1) Count the total number of valence electrons (1) for all atoms for Example: H2O H: Column 1 so O: Column 6 so Total: 1 electron x 2 = 2 electrons 6 electrons = 6 electrons 8 electrons (2) Decide on a central atom – usually the single (2) atom – and place the others around it. atom H O H (3) Add one single bond to attach all (3) surrounding atoms to the central atom (but NOT to each other). H–O-H Molecules and Models Molecules Each bond counts as 2 valence electrons. Each (4) Place remaining electrons, a pair at a time, (4) around the atoms to give each a full shell (usually 8, 2 for hydrogen). It usually works best to fill the outer atoms first and the central atom last. the 2 bonds - 4 electrons already placed, 4 electrons still bonds available available .. H–O–H → H-O-H .. (5) Check octet rule – do all atoms have a full (5) .. shell? H - O - H .. 2 on H 8 on O 2 on H Molecules and Models Molecules (6) If any atom (usually the central one) is short (6) of a full octet, take a lone pair off a neighboring atom and move it to form another bond with the central atom. central Not needed here .. H-O-H .. Waves of Light Waves Electromagnetic spectrum A continuum of waves ranging from very low energy (long continuum wavelength) radio waves to very high energy (short wavelength) X-rays and gamma rays wavelength) Waves of Light Waves Radiation from the sun Includes most of the electromagnetic spectrum, Includes but not all wavelengths/energies equally but Waves of Light Waves Wavelength (λ) length from the crest of one wave to the crest length of the next of Given in meters (or nm, or mm, etc) Waves of Light Waves Frequency (ν ): the number of waves that pass a given point in the one second one Given in Hertz (Hz) or 1/s = s-1 (really cycles/second) cycles/second) Speed of light (radiation): Speed A constant: 3.00 x 108 m/s All light (radiation) moves at this speed, no matter what the wavelength or frequency. matter Waves of Light Waves Calculating Wavelength and Frequency Every wavelength has a specific frequency. c = ν x λ (speed of light) = (frequency) x (wavelength in meters) Radiation and Matter Radiation Energy (E): Every wavelength/frequency of radiation also has a Every specific energy specific Photon – particle of light, individual bundle of energy Given in Joules (J) Calculating Energy E= h x x ν c) / λ Energy = Energy Planck’s constant x frequency E = (h Energy = (Planck’s constant x speed of light) / wavelength h = 6.63 x 10-34 J s (Joules x seconds) Radiation and Matter Radiation The amount of energy radiation has affects The amount how it interacts with matter. interacts Microwaves: rotate water molecules Microwaves: IR: bending and stretching of bonds, this is heat energy Visible: interacts with retina triggering sight, some triggers Visible: photosynthesis photosynthesis UV: electronic excitation (electrons kicked up to higher UV: energy levels), some ionization (electron removed) and bond breaking breaking X-ray and gamma ray: bond breaking and ionization Oxygen/Ozone Shield Oxygen/Ozone BOTH oxygen and ozone protect us from BOTH high energy radiation, with one difference: high O2 absorbs only radiation with an energy only 19 higher than 8.22 x 10--19 J higher That is about the energy needed to break the That O=O double bond. O=O O2 + photon → 2O photon of E ≥ 8.22 x 10-19 J, λ ≤ 242nm Oxygen/Ozone Shield Oxygen/Ozone O3 absorbs radiation with energy as low as 6.22 x 10-19J as Most radiation missed by O2 that is still harmful can be absorbed by O3 harmful O3 + photon → O2 + O photon of E ≥ 6.22 x 10-19 J, λ ≤ 320nm Oxygen/Ozone Shield Oxygen/Ozone Sun A C B O3 O2 & O3 Earth Oxygen/Ozone Shield Oxygen/Ozone Oxygen/Ozone Shield Oxygen/Ozone Natural Ozone Formation and Depletion: Natural The Chapman Cycle The O2 +UV photon (≤242nm → 2O ) Collisions (fast) O +O2 ⇔ UV photons Collisions (slow) O3 +O → O3 2O2 Oxygen/Ozone Shield Oxygen/Ozone Natural Ozone Formation and Depletion: Natural The Chapman Cycle The O2 +UV photon (≤242nm → 2O ) Collisions (fast) O +O2 ⇔ UV photons Collisions (slow) O3 +O → O2 absorbs UVC, which breaks its bond form O ing O3 2O2 Oxygen/Ozone Shield Oxygen/Ozone Natural Ozone Formation and Depletion: Natural The Chapman Cycle The O2 +UV photon (≤242nm → 2O ) Collisions (fast) O +O2 ⇔ UV photons Collisions (slow) O3 +O → O2 absorbs UVC, which breaks its bond form O ing M of these O collide with another O2 to formO3. ost If the O3 absorbs a UVC or UVB photon the bond breaks again. O3 2O2 Oxygen/Ozone Shield Oxygen/Ozone Natural Ozone Formation and Depletion: Natural The Chapman Cycle The O2 +UV photon (≤242nm → 2O ) Collisions (fast) O +O2 ⇔ UV photons Collisions (slow) O3 +O → O2 absorbs UVC, which breaks its bond form O ing M of these O collide with another O2 to formO3. ost If the O3 absorbs a UVC or UVB photon the bond breaks again. O3 can also be rem oved fromthe cycle by colliding with an O fromthe first reaction to form2 O2. 2O2 O3 3 x 108 tons of O3 both formed and destroyed each day Oxygen/Ozone Shield Oxygen/Ozone The steady state concentration depends The on: on: Intensity of UV concentration of O2 and other reacting species temperature rates and efficiencies of reaction steps these all vary by altitude Seasonal variations Sun cycle Winds Biological Effects of UV Radiation Biological UV radiation (and anything more UV energetic) breaks bonds in biological tissue tissue Low dose – cancer 6% decrease in O3 = 12% rise in skin cancer Higher dose of very high energy radiation Higher death death Biological Effects of UV Radiation Biological Notice more skin cancer/sunscreen ads recently? Retina damage Cataracts (UV-B) – 10% O3 decrease = 2 million new cases new Damage to young marine life Evidence of damage to DNA in Antarctic ice fish Plant growth suppressed UV-B damages phytoplankton – important for UV-B ocean food chain as well as for absorbing manocean made CO2 Stratospheric O3Destruction Stratospheric Natural Ozone Destruction H2O Around 5ppm in upper atmosphere H2O + UV photon →H● + ●OH (free radicals) UV →H● Free radicals attack O3, breaking it down to O2 NO From microorganisms in soil and ocean ●NO – a natural free radical Attacks O3 Stratospheric O3Destruction Stratospheric Expected O3 Levels 320DU in the northern hemisphere 250DU at equator Below 220DU is considered a “hole” Chlorofluorocarbons (CFCs) Chlorofluorocarbons Chief man-made O3 destroyer Compounds made up of C, Cl and F Not naturally occurring Chlorofluorocarbons (CFCs) Chlorofluorocarbons Uses: Refrigerant (refrigerators and air conditioners) Right boiling point Right Not toxic (like NH3 and SO2, old refrigerants) Not Very stable, non-reactive Non-flammable Cheap Propellant for aerosol cans (not anymore) Gases blown into plastic foams Solvents for grease Sterilizers Fire extinguishers (usually with Br) Chlorofluorocarbons (CFCs) Chlorofluorocarbons Production and Release of CFCs By 1985 By international production of CFC-11 and CFC-12 = 850,000 tons; some escaping into atmosphere. 850,000 Ground level CFCs at .6ppb and rising 4% annually Chlorofluorocarbons (CFCs) Chlorofluorocarbons UV Photon (λ≤220nm) CCl2F2 → •CClF2 + •Cl (reactive free radical) Ozone Layer CFCs – stable at low altitude Chlorofluorocarbons (CFCs) Chlorofluorocarbons How does •Cl destroy O3? •Cl is a catalyst Cl catalyst a chemical substance that participates in and speeds up a chemical reaction without undergoing a permanent change undergoing A single catalyst atom/ molecule can catalyze thousands of reactions thousands Chlorofluorocarbons (CFCs) Chlorofluorocarbons Ozone destruction 2 •Cl + 2O3 → 2 •ClO + 2O2 •ClO + •ClO → ClOOCl ClOOCl + UV photon → •ClOO + •Cl •ClOO + UV photon → •Cl + O2 Net Reaction: 2O3 → 3O2 One •Cl can destroy up to 100,000 O3 molecules One before being carried back to the lower atmosphere before Most O3 destruction is @ ~40km, above the densest Most O3 region The Antarctic Ozone Hole The The Antarctic Ozone Hole The C l● ClONO2 HCl (safe molecules) HOCl Cl2 sulfates Nitric acid Polar Stratospheric Clouds (Ice Crystals) Responses to O3 Depletion Responses Bans on use 1978 – banned in spray cans (North America) 1990 – discontinued as foaming agent in 1990 plastics (North America) plastics 1985 – Vienna convention on the Protection of 1985 the Ozone Layer the 1987 – Montreal Protocol on Substances that 1987 Deplete the Ozone Layer agree to reduce CFC production to ½ 1986 level by 1998 1998 1990 - 100 nations agree to ban all production by 1990 2000 2000 later - 140 nations agree to ban all production by 1995 later (now 183 nations have agreed to this) (now Replacements for CFCs Replacements Replacements must be non-toxic (like CFCs) non-flammable (like CFCs) have BP in the correct range to use as have refrigerant refrigerant EITHER extremely stable in the stratosphere, EITHER so they don’t break down and destroy ozone, OR degradable at ground level OR Replacements for CFCs Replacements Fluorocarbons (C and F only) Non-toxic Non-flammable Very stable in upper atmosphere BUT build up and act as greenhouse gases Chlorocarbons (C and Cl only) OK boiling point Too many chlorines – toxic Replacements for CFCs Replacements Hydrochlorofluorocarbons (H, Cl, F, C) Hydrochlorofluorocarbons (HCFCs) (HCFCs) Reduced stability – break down in lower Reduced atmosphere atmosphere Too many Hs and BP is too low, flammability Too too high too Some have been successful Replacements for CFCs Replacements HCFC-22 + 5% ozone depleting potential of CFC-12 + short lifetime (20 years) short - only an interim solution – does have some only adverse effects adverse - production must stop by 2030 (1992 production Copenhagen amendments to MP) Copenhagen Results Results Results Results Looking to the Future Looking Difficulties of phasing out CFCs and phasing in Difficulties replacements: replacements: Replacements aren’t quite as good as CFCs Replacements (boiling points, costs, etc.) (boiling Deciding who should test and regulate new Deciding compounds compounds Economic interests of those using them in their Economic products products Developing nations cannot afford more Developing expensive replacements expensive CFC emissions in developing countries could CFC be 1 million tons by 2010 be Financial assistance is needed from Financial industrialized nations to make this possible industrialized ...
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This note was uploaded on 04/11/2011 for the course CHEM 102 taught by Professor Henshaw during the Winter '11 term at Grand Valley State University.

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