The Fermi energy of aluminium is 11.66 eV; its density is and its molar mass is . From these data, we have to determine the number of free electrons per atom.

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We will calculate first the number of atoms of aluminium per cubic meter. It is given by the relation

We use the following data:

We find

We calculate next the number density of conduction electrons per cubic meter from the Fermi energy .

We recall that

where is the number of conduction electrons per cubic meter. The Fermi energy of aluminium is 11.66 eV. Therefore,

The number of conduction electrons per atom of aluminium will therefore be given by