Protecting the Ozone layer

E + O2 ---> O3

Ozone - O3 - Allotrope or Allotropic

2 forms of the same element that differ in their molecular or crystal structure & hence their properties


Nucleus - protons (+) ---> atomic #

+neutrons (NC)

Atomic Mass ---> Isotopes

Electrons (-) -> ion

1. responsible for periodicity of properties

2.levels or shells

a)­ d ÿ attraction

b)­ d ÿ energy

outer e- most important for accounting for similarity in chemical. props

"If you understand bonding you’ll understand chemistry" A.D. 1890

Single or covalent bond 2 shared e-

H:H Lewis structure named after Joe Bxsfts

Octet Rule - you want to fill the outer orbit with Eight (8) e- Þ the orbits hold Þ 2, 8, 8

What if you have 6 or 4 electrons?

.. .. .. ..

O:: O or O = O

.. .. .. ..

:N:::N: or :NºN:

Double bonds

1. shorter

2. stronger

3. harder to break

This is modeling Þ ozone (O3)

O - O = O

O = O - O



All this is a General Rule to guide you. Look @ p.41-44 Lewis Structures

Light - separate O.H.

The Oxygen/Ozone Screen


O2 + photon Æ 2O

UV Æ l < 242 nm (10-5 Æ10-6 cm) or 1 x 10 -9m


O3 + photon Æ O2 + O

UV Æ l < 320 nm

**Bonds are E specific!!!**

So O2 can screen the hi E UV ---> plants thrive

What about UV 242 - 320 nm?

Ozone more reactive than O2 what does this suggest about its bonding?

So what happens to UV reaching the Earth’s surface?

UV & You

To tan or not to tan? That is the question.

ÿ l F ­ E ­ DNA Damage­

Geographic location is most important!!!

40 km S. latitude = 1% O3 ÿ

Every day 300,000,000 tons of O3 DESTROYED!!!!!!

Steady State

O3=O3 destruct

Chapman Cycle pg 52 -53

Why are there arguments

1. Concentrations vary

2. intensity, of radiation varies

3. temperature change

4. react rate changes w/altitude

Ozone Distribution (Fig 2.7, p. 54)

NOTE - Log scale with error bars

Paths for O3 destruction

UV photon + H2O Æ H · + ·OH

Note Æ · is an unpaired electron

The ·H and ·OH (hydroxyl) are FREE RADICALS. (the · can go anyplace - H· )

Free radicals are unstable chemical species with unpaired electrons. They are highly reactive.

The following is not in your text

H· + O3 Æ OH· + O2

OH· + O Æ H· + O2

We can combine this into one equation

+ OH· + O3 + O Æ H· + OH· + O2 + O2



O3 + O Æ 2O2

Catalyst - chemical substance that participates in a reaction and influences its speed of reaction without undergoing a permanent change

Why It takes 6 hrs to London.

SST flies @ 15 - 20 km & ?

E + N2 + O2 Æ 2NO· (free rad)

Where Did All The Ozone Go?

320 DU in NH vs 250 DU in Quito - Why?

CFCs are chlorofluorocarbons

CFC -12 is Freon - 12 ->

CF2Cl2 or CCl2F2

The Lewis structure is very easy



Cl - C - Cl



Halogens - Family 7A

Fluorine is the most reactive element

Halogen compounds are very common, esp. Cl

CFCs however are very inert -> 120 yrs. at sea level

But .....

CCL2F2 + E (UV) Æ CClF2 +Cl·

l £ 220 nm

Cl· + O3 Æ ClO· + O2

ClO· + O Æ Cl· + O2 or

Cl· + ClO· + O3 + O Æ 2O2 +Cl· + ClO·

the Cl is catalyzing O3 destruction! ~100,000 O3 molecules before being carried into the lower atmosphere (<30km) to form HCl and ClONO2

Is man the only cause?

Natural (Fig 2.11, p.61)


But what about the Antarctic O3 Hole?

What to do?

1. Go back to iceboxes - yeah right!!!

How your ‘fridge works - (OH, Fig. 2.10, p.59))


1.toxicity ---> rem NH3 & SO2

2. flammability

3. extreme stability

how about? F


F -- C -- F


F This ­ IR absorption!

1. Add an H? BOOM!!!

2. Add a Cl? UGHHHHH....

composition, molecular structure, BP

these all ÿ Eff ­ E

The Big Mac and You