In order to talk about electricity, you have to look at the role of electrons in the grand scheme of things. In a bulk material, whether it be composed of atoms of similar or dissimilar elements, valence electrons are the glue that holds the whole mass together. [Bulk materials are everything you see around you. Scientists talk about carbon atoms and molecules, but these things are very rarely sitting around all by themselves. Even a small piece of copper wire would be composed of billions and billions of copper atoms.] The stronger the bonds between those atoms, the more tightly bound the electrons will be to those atoms. In conductive materials, some valence electrons are able to free themselves and leap frog around the bulk material, replacing other electrons along the way. Metals like copper are not only conductive, but also malleable (or "bendable"). This is because the atoms of the metal are weakly held together and can "mush" around to take on a new shape. Ceramic materials are strong insulators and comparatively fragile. What doesn't bend, breaks.

To go into more detail, conductivity is measured by the difference in energy between the valence and the conduction bands of the bulk material. If you are familiar with bonding and anti-bonding orbitals of molecular bonds, you can think of valence and conduction bands as the bonding and anti-bonding orbitals for the bulk material. A simple illustration of this is the hydrogen- hydrogen bond of hydrogen gas (H2). The two electrons are in constant motion in, around, and through the two atoms. The compound is at it's most stable (lowest energy) state when the two electrons are equally shared between the two nuclei. This is the bonding orbital. The compound would be least stable when the two electrons are on opposite sides of each nuclei from one another. The latter example is referred to as an anti-bonding orbital because the protons would be face to face and their mutual positive charges would repel one another, breaking the molecule apart. Just like molecular bonds are a composite of all their constituent atomic bonds, valence and conduction bands are a combination of bonding and antibonding orbitals of all the constituent bonds holding the bulk material together. The weaker those bonds (i.e. the smaller the difference in energy between the valence and conduction bands) the easier it is to displace a valence electron and allow it to migrate through the material. In other words, in highly conductive materials it is easy to displace one of the valence electrons to jump from atom to another in the direction of the current.

Regards,

Marc