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Radiation and Radicals
Ways of breaking bonds

All reactions involve the breaking and remaking of bonds.

Breaking bonds is sometimes called bond fission. The way that bonds break has an
important influence on reactions.

In a covalent bond, a pair of electrons is shared between two atoms

E.g. in the…

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Heterolytic Fission
In this type of fission, both of the shared electrons go to just one of the atoms
when the bond breaks.

This atom becomes negatively charged, because it has one more electron than it has

The other atom becomes positively charged.

In the case of HCl


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They key feature of a radical is its unpaired electron, which makes it particularly

The unpaired electron is often shown as a dot.

Showing all Showing the Showing none
the outer unpaired of the
electrons electron only electrons

Sometimes the dot is omitted together and a chlorine radical…

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Radicals are Reactive
Filled outer shell electron shells are more stable than unfilled ones.

Radicals are reactive because they tend to try and fill their outer shells by grabbing an
electron from another atom or molecule.
For example, when a chlorine radical collides with a hydrogen molecule, the chlorine grabs…

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Radical Chain Reactions
Like all radical chain reactions, this reaction has three stages:

Initiation, propagation and termination.

Initiation Chlorine radicals are initially formed by the photodissociation of chlorine

Cl2 + hv Cl · + Cl ·

Only a few chlorine radicals are formed, but they are so reactive that…

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Methane and Chlorine
Apart from their use as fuels, alkanes are generally considered to be unreactive, which they
are with polar or organic solvents. However, alkanes will react with chlorine, and other
halogens, in the presence of light. For example, methane and chlorine do not react at all in


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