OZ 3: How is Ozone formed in the atmosphere?

bond fission

bond breaking

What does bond fission involve?

redistribution of electrons in the covalent bond

What are two methods of bond fission?

1. heterolytic

2. homolytic

heterolytic fission

both of the shared electrons go to one of the atoms

both of the shared electrons go to one of the atoms

heterolytic fission

Heterolytic bond fission is common in __________ bonds

polar

Homolytic fission

shared electrons go to one atom each

shared electrons go to one atom each

Homolytic fission

unpaired electrons have a ________ _________ to pair up again with an __________ from another substance

strong tendency

electron

Radicals are commonly formed when bonds are ________ but _________ can also break like this especially in ________ state and presence of _________

non-polar

polar

gas

light

amount of energy taken for bond fission depends on the

bond enthalpy

Equation for formation of ozone

O + O₂ —→ O₃

What is one way to make oxygen atoms?

dissociating dioxygen molecules

Where does the high energy for dissociating oxygen molecules come from?

UV radiation or electric charge

Why can you smell sharp odour of ozone near photocopiers, UV lamps or electric motors?

electric dischargers make dioxygen molecules in the air dissociate

In the troposphere oxygen atoms are produced by the action of _________ on the pollutant gas ____________ ____________

sunlight

nitrogen dioxide

In the stratosphere, oxygen atoms are formed by the ___________ of __________ molecules when _______ radiation of the right _____________ is absorbed

photodissociation

dioxygen

UV

frequency

Reaction for breakdown of dioxygen in the stratosphere

O₂ + hv → O + O

Chain reaction after dioxygen molecules have been dissociated in stratosphere

O + O₂ → O₃

O + O → O₂

O + O₃ → 2O₂

Reaction for the break down of ozone when UV radiation is absorbed

O₃ + hv → O₂ + O

What is radical polymerization?

A process where radicals initiate polymer chain growth

What stops radical polymerization?

Termination reactions or depletion of monomers

What type of reaction is combustion?

A radical chain reaction

What is the role of flame-retardant additives?

They reduce radical propagation to prevent auto-ignition

What effect do radicals have on DNA?

They cause DNA cross-linking, which can lead to cancer

How do radicals affect fats and proteins?

They cause cross-linking, leading to wrinkles

How can radicals contribute to heart disease?

They oxidize low-density lipoproteins, leading to arterial plaques

How do antioxidants help prevent radical damage?

They donate electrons to radicals without becoming unstable

Give an example of an antioxidant.

Vitamin C

Why are radicals reactive?

they have unfilled outer shells

Reaction of Cl with H₂

HCl + H

What does a curly electron indicate?

movement of an electron

half-headed curly arrow

one electron

full-headed curly arrow

pair of electrons

tail

where electron starts

head

where electron ends

3 parts of a radical chain reaction

1. Initiation

2. Propagation

3. Termination

Where are radicals found in initiation?

product side

Where are radicals found in propagation?

both sides

Where are radicals found in termination?

reactant side

Alkanes will react with ___________ in the presence of _________

halogens

light