Protecting the Ozone Layer
Isn’t ozone hazardous to human health?
What can we do (if anything) to
help stop the depletion of our ozone layer?
Why do we need to protect the ozone layer?
Why is the ozone layer getting smaller?
What is the Ozone Layer?
The Ozone Layer
• Ozone, O3, is a health hazard in the troposphere, but essential to life on earth in the stratosphere.
The Ozone Layer
• Ozone, O3, is a health hazard in the troposphere, but essential to life on earth in the stratosphere.
Energy + 3 O2 2 O3
Energy must be absorbed (endothermic) for this reaction to occur.
Ozone Formation
Energy + 3 O2 2 O3
Ozone is an allotropic form of oxygen.
Energy must be absorbed (endothermic) for this reaction to occur.
Element Allotropesoxygen O2, O3
carbon graphite, diamond, charcoal
An allotrope is two or more forms of the same element that differ in their chemicalstructure and therefore their properties.
The Regions of the Lower Atmosphere
Atmospheric pressure changes with altitude
The Regions of the Atmosphere
Why does it take longer to cook an egg in Denver than it does in New Orleans?
There is less air pressure at higher altitudes. Water boils when the vapor pressure of the water molecules exceeds that of the localized air pressure. Because there is less air pressure at higher altitudes, more energy must be supplied (longer time) to get the temperature of the water high enough to cook the egg.
Altitude record for plane flight – 31,000 m by an SR-71 on its retirement flight.
The ozone layer is a region in the stratosphere with maximum ozone concentration.
O8
16.00
Atomic number (Z)
Mass number (A)
– The number of protons (nuclear charge)
– The sum of the protons and neutrons
2.2
Isotopes are two or more forms of the same element (same number of protons) whose atoms differ in number of neutrons, and hence in mass.
Isotopes of carbon: C-12, C-13, C-14 also written as: 12C 13C 14C
Isotopes are two or more forms of the same element (same number of protons) whose atoms differ in number of neutrons, and hence in mass.
Hydrogen has exactly three isotopes – 1H – Majority isotope in nature. Hydrogen
2H – Deuterium. Only about 0.0026 - 0.018% in nature. Stable. Sometimes called heavy hydrogen.
3H – Tritium. Half life of only 12 years, so only trace amounts in nature. Radioactive, but only weakly, and not harmful to humans externally. Used in watch dials.
Isotopes are two or more forms of the same element (same number of protons) whose atoms differ in number of neutrons, and hence in mass.
Uranium has three main isotopes – 238U – Majority isotope in nature. Radioactive, but not capable of uncontrolled fission – can’t make a bomb.
235U – Only about 0.7% in nature. Enriching to 4% allows nuclear power. Enriching to >50%, it can explode.
233U – Only about 0.005% in nature. Not as strong a slow neutron source as 235U, but more than 238U
Let’s go back to the Periodic Table
The Bohr Model
• This is a MODEL of the atom that links electron behavior (microscopic) to the periodic law (macroscopic).
Let’s go back to the Periodic Table
Valence Electrons
• Valance Electrons– Electrons in the Outermost Principal
Shell– Which simply means the
electrons that fill the orbitals for the main-group elements
– That means there are always a maximum of either two (first row) or 8 (all the others)
– Electrons Involved in Chemical Bonding
Valence Electrons
Valence Electrons
Li Be
B
C
N
O
F
Ne
The group number (of the representative elements) on the periodic table tells you the number of valence electrons.
1A
2A 3A 4A 5A 6A 7A
8A
Group 1A: 1 valence electron
Group 3A: 3 valence electrons
Representing molecules with Lewis structures:
Consider water, H2O: OH H
Representing molecules with Lewis structures:
Consider water, H2O: OH H
Representing molecules with Lewis structures:
Consider water, H2O:
1. Find sum of valence electrons: 1 O atom x 6 valence electrons per atom = 6
+ 2 H atoms x 1 valence electron per atom = +2 8 valence
electrons
OH H
Representing molecules with Lewis structures:
Consider water, H2O:
1. Find sum of valence electrons: 1 O atom x 6 valence electrons per atom = 6
+ 2 H atoms x 1 valence electron per atom = +2 8 valence
electrons2. Arrange the electrons in pairs; use whatever electron pairs needed to connect the atoms, then distribute the remaining electron pairs so that the octet rule is satisfied:
OH H
lone pair
bonding pair
OH H
Representing molecules with Lewis structures:Typical valence for selected atoms = the # of bonds an atom typically forms
Element Typical valence
Classification
H,
X (X= F, Cl, Br, I)
1 monovalent
O 2 divalent
N 3 trivalent
C 4 tetravalent
Representing molecules with Lewis structures:
Multiple bonds
O O H C C H
Triple bondDouble bond
Occasionally, a single Lewis structure does not adequately represent the true structure of a molecule, so we use resonance forms:
N
O
O ON
O
O ON
O
O O
Light and Matter
• Light has a very important connection to all this.– Light interacts with matter by either being reflected or
absorbed.
The Nature of Light
Low E
High E
Wavelength () = distance traveled between successive peaks (nm).
Frequency () = number of waves passing a fixed point in one second
(waves/s or 1/s or s–1 or Hz).
The Electromagnetic Spectrum
The various types of radiation seem different to our senses, yet they differ only in their respective and
Visible: = 700–400 nm
Infrared (IR): longest of the visible spectrum; heat absorptions cause molecules to bend and stretch.
Microwaves: cause molecules to rotate.
Short range: includes UV (ultraviolet), X-rays, and gamma rays.
R O Y G B I VDecreasing wavelength
Increasing Energy
The energy of a photon of electromagnetic radiation
is calculated by: E = hwhere h = 6.63 x 10–34 J.s (Planck’s constant)
The wavelength and frequency of electromagnetic
radiation are related by: c =
where c = 3 x 108 m/s (the speed of light)
Energy and frequency are directly related –higher frequency means higher energy.
The Chapman Cycle
2 242
242
2
:: : :: :
UV Photonsnm
UV Photonsnm
O O
O O O O
The Chapman Cycle
2 242
242
2
:: : :: :
UV Photonsnm
UV Photonsnm
O O
O O O O
The Chapman Cycle
A steady state condition
≤
≤
+
+
The Chapman Cycle
A steady state condition
≤
≤
+
+
Biological Effects of Ultraviolet Radiation
The consequences depend primarily on:
1. The energy associated with the radiation.
2. The length of time of the exposure.
3. The sensitivity of the organism to that radiation.
An Australian product uses “smart bottle” technology; bottle color changes from white to blue when exposed to UV light.
The most deadly form of skin cancer, melanoma, is linked with the intensity of UV radiation and the latitude at which you live.
First, UV radiation breaks a carbon-halogen bond:
Photon < 220 nm) + CCl2F2 .CClF2 + Cl. (free radicals)
How CFCs Interact with Ozone
CFC-11 CFC-12Freon 11 Freon 12
trichlorofluoromethane dichlorodifluoromethane
C
F
Cl
Cl
Cl C
F
F
Cl
Cl
CCl3F CCl2F2
2 Cl. + 2O3 2 ClO. + 2 O2
2 ClO. ClOOCl
The chlorine radical attacks an O3 molecule:
Then two chlorine monoxide radicals combine:
UV photon + ClOOCl ClOO. + Cl.
ClOO. Cl. + O2
The ClOOCl molecule then decomposes:
The net reaction is: 2 O3 3 O2
The Cl. radicals are free to attack more O3
The Cl. radicals are both consumed and generated; they act as catalysts
Experimental analyses show that as ClO. concentrations increase, ozone concentration decreases.
Change in size of the ozone hole over for last decade
Another look at the ozone hole. The more blue, the worse the problem….
HCFCs are alternatives to CFCs: they decompose more readily in the troposphere so they will not accumulate to the same extent in the stratosphere.
HCFC-22chlorodifluoromethane
CHClF2
HCFC-141bdichlorofluoroethane
C2H3Cl2F
C
F
F
Cl
H C
Cl
F
Cl
C
H
H
H
Refrigerants for Automobile Use
Freon in your car’s air conditioner is a commonly used CFC