F332 reaction mechanisms for the atmosphere

In the spec it says that you should be able to: 

  • describe the difference between homolytic and heterolytic bond fission and recognise examples; 
  • recall the formation, nature and reactivity of radicals and explain the mechanism of a radical chain reaction involving initiation, propagation and termination;
  • use a radical mechanism as a model to explain the reaction of alkanes with halogens a radical chain reaction in the presence of UV radiation to form halogenoalkanes);
HideShow resource information

Difference between homolytic and heterolytic fissi

Heterolytic fission

The bond breaks unevenly where the electron bond pair can stick with one fragment and a positive and negative ion form.

(http://www.docbrown.info/page06/ELmcTEST/heterofission.gif)

where as in homolytic fission the bond breaks evenly here the bonding pair of electrons are equally divided between two highly reactive fragments called free radicals.


1 of 6

What is a radical?

Free radicals are characterised by having an unpaired electron not involved in a chemical bond.

It wants to pair up with another electron to form a stable bond - that's why free radicals are so reactive!

2 of 6

Initiation

In Initiation free radicals are formed.

1:

UV light provides enough energy to break the bond-photodissociation

2:

The bond splits equally and each atom gets to keep one electron (homolytic fission)

The atom becomes a highly reactive free radical, because of its unpaired electron

3 of 6

Propogation

Propogation-

  • the free radicals form a new bond
  • as well as producing a new free radical
  • it continues the reaction in a chain reaction.
4 of 6

Termination

  • Highly reactive free radicals
  • 2 unpaired electrons form a new bond
5 of 6

Mechanism

I can't find a decent diagram but when drawing this be sure to:

  • use single headed arrows to show the movement of one electron.
  • draw the arrows starting from the bond to the atom
6 of 6

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all Reactions resources »