Why is Al3 a conductor and Aluminum Trioxide is not?
This is almost a hand-waving argument. A complete explanation will be very complex.
In a crystal of Al (not Al3), the 3 valence electrons from each Al atom are not attracted in any specific direction. The surrounding atoms are also Al atoms, each of which has these 3 electrons. So what ends up happening is that a large number of these electrons become free to wander about the crystal any which way they choose. This "sea" of electrons is what makes Al a conductor (the electrons will carry charge and energy from one end of an Al rod to another if the correct potential is provided, because there is little impedance to there movement).
But in the case of Al2O3, each Al atom is surrounded by a bunch of O atoms. O being a strongly electronegative atom, tends to attract the valence electrons towards itself. So, all these electrons get more or less bound by these O atoms, and as a result they are not free to move about the crystal. So, it takes a large activation (whether thermal or electrostatic) to force these electrons to move. This is basically saying that Al2O3 is a poor conductor.
Ummm...this isn't homework, is it ?
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