Section 1–2

• Insulating materials have very few free electrons and do not conduct current at all under normal circumstances;
• Materials that are conductors have a large number of free electrons and conduct current very well;
• Semiconductive materials fall in between conductors and insulators in their ability to conduct current;
• Semiconductor atoms have four valence electrons. Silicon is the most widely used semiconductive material;
• Semiconductor atoms bond together in a symmetrical pattern to form a solid material called a crystal. The bonds that hold a crystal together are called covalent bonds;