The Role Of Electrons
Electrons do not spin just anywhere around the nucleus, they are found in shells or energy levels which are numbered 1, 2, 3 and 4 and named K, L, M and N. It is easy to picture these shells if we imagine a pea as the nucleus of our atom. The pea sits in the middle of a table tennis ball (the first of K shell). All this sits in inside a tennis ball (second or L shell), which sits inside a basket ball (third or M shell) which sits inside a beach ball (fourth or N shell).
The Electron: Crash Course Chemistry #5
About 80% of the elements in the periodic table are metals. Another smaller set of elements are classified as non-metals. Separating the metals and non-metals is a set of elements that act like a little bit of both (the metalloids).
Tom Lehrer's "The Elements" animated