What makes an atom a good conductor?

Very little electric force is required to cause electron flow in conductors. This is due to electrons called "free electrons", which exist in the atoms of conductors. "Free electrons" are electrons that are very weakly bonded to the atom. ... Metals such as copper, silver, and gold are good conductors.

Well, atoms are loosely bound and free to move through the material. Almost all, or just most, atoms will hold on to electrons very tightly and are insulators.