Conductors and Insulators

Materials split into two camps based on how easily electrons move through them. Conductors like copper and aluminum let electrons flow freely — their outer electrons are barely attached. Insulators like rubber and glass hold their electrons tight.

Then there are semiconductors — materials like silicon that sit on the fence. Add a tiny impurity called doping and they become controllable conductors. This trick is the foundation of every computer chip, LED, and solar cell on Earth.