OZ.3 Flashcards
Radical reactions.
what is the bond breaking process in a reaction of covalent molecules also known as and what does it involve?
Bond fission, which involves the redistribution of electrons in the covalent bond.
What are the two types of bond fission?
Heterolytic fission and homolytic fission.
What happens to the pair of bonding electrons in heterolytic fission and what happens to the atoms in the covalent molecule?
In heterolytic fission, both of the shared electrons go on to one of the atoms when the bond breaks, making that atom a negatively charged ion and the other a positively charged ion.
When does heterolytic fission generally happen?
When the bond is already polar.
What happens to the pair of bonding electrons in homolytic fission and what happens to the atoms in the covalent molecule?
In homolytic fission, one of the two shared electrons goes to each atom. The radicals produced is shown by having a dot beside the atoms, representing the electron it has inherited from the bond. However the atoms will have no overall charge because the have the electronic structure of their elemental form.
When does homolytic fission generally happen?
When the bond is non polar.
Can homolytic fission take place with polar molecules?
Yes, particularly when the reaction is taking place in the gas phase and in the presence of light.
What is photochemical dissociation (photodissociation)?
Is the process of breaking molecules apart in the presence of light radiation.
Does every bond require the same amount of energy to break?
No, the amount of energy it takes depends on the bond enthalpy of the bond being broken.
How is ozone formed in the stratosphere?
Photochemical dissociation of dioxygen molecules to form two oxygen radicals and an oxygen radical can then collide and react with dioxygen molecule to form ozone.
What is required for the photochemical dissociation of dioxygen molecules and how can it be provided?
Energy will need to be absorbed for dioxygen molecules to break and this energy can be provided by ultraviolet radiation.
What happens when ozone molecule absorbs ultraviolet radiation?
It will undergo photochemical dissociation and split up and give dioxygen molecule and a oxygen radical.
Why are radicals so reactive?
Because they don’t have a full outer electron shell, therefore they tend to try to fill it by grabbing an electron from another atom or molecule.
What is meant by a radical chain reaction?
It is a chain of reaction where radicals produced in one reaction starts another reaction and that goes on.
What are the three stages of a radical chain reaction?
- Initiation
- Propagation
- Termination
