Reactivity 3.3

Both electrons are retained by one of the bonding atoms to form ions when a covalent bond is broken

One electron is retained by each atom when a covalent bond is broken to form free radicals

Any chemical entity that has an unpaired electron.

Highly reactive, electrically neutral (due to same number of protons/electrons), have an unpaired electrons

When exposed to UV light

Energy is supplied to a hydrocarbon by UV light, photochemical free-radical substitution reactions with halogens can be performed.

Initiation, propagation and termination

UV light supplies energy required to break Cl-Cl bonds homolytically to form chlorine free radicals

Chlorine free radicals react with an alkane to remove a hydrogen atom, forming HCl and propagating a free radical. Free radical is methyl radical and can continue to react and continue the propagation process

In theory the propogation process can continue forever. However it can also be terminated by the radical escaping the system, colliding with the walls of the vessel or by reacting with other radicals.

The H radical is never formed

Shows movement of an electron in propagation and termination steps

Shows movement of a pair of electrons

The higher energy (UV) is required to break

Oxygen molecules absorb high energy radiation, form oxygen radicals which combine with oxygen molecules to form ozone

3O2 –> 2 O 3