Free Electrons

Free Electrons:

As we have already seen, electrons move around an atomic sheel in various discrete orbital paths at varying distances from the nucleus. Each of these paths represents a shell where the electron has a specific energy. The higher the energy, the greater the radius of the orbital path. Electrons in the outermost shell thus have the highest amount of energy and are less closely bound to the atom than electrons in the inner shells. Electrons such as these are called valence electrons. The exchange of these electrons is responsible for the formation of an atomic lattice. The way an element's atoms bond together depends on how the valence electrons of each atom can become linked in pairs. This linking of atoms gives rise to characteristic properties of the element that are dependent on the valence electrons of individual atoms in the atomic lattice.

The following graphic depicts a simplified model of a copper atom. It has two atoms in the first and innermost shell, eight electrons in the second shell, eighteen in the third and one valence electron in its outermost shell. 

Since valence electrons are only weakly bound to the atomic nucleus, a sufficient quantity´of energy can cause them to leave their orbit altogether, so that they are no longer part of the atom at all. This leads to the phenomenon of free electrons. These can effectively move more or less freely from one atom to the next within the atomic lattice of a substance. These free electrons play a key role in the conductivity of materials.

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