Final answer:
A substance lacking free electrons in its outer shell which does not conduct electricity effectively is called an insulator.
Step-by-step explanation:
A substance that doesn't have a free electron in the outer ring is called an insulator. These materials have bound electrons that are not free to move around and therefore do not conduct electricity effectively. On the other hand, a semiconductor is a substance that conducts electricity better than an insulator but not as well as a conductor. Semiconductors like silicon have unique properties that allow their conductivity to be influenced by the addition of impurities, which is a principle used in making electronic components such as microchips.