Re: why are metals good conductors of electricity while plastics are excellent insulators?

JR,

The conductivity of a material is determined by the energy needed to excite
electrons in the outer most shells of its atoms or molecules.  Once the
electrons are excited, they can move around the material.  An electric
current is actually a stream of electrons playing "leap frog", jumping from
one atom to the next.  The greater the energy needed to excite the
electrons (or the more strongly bound the electrons are to the nuclei of
their atoms), the more insulating the material.

-Marc