Carbon is an element known from antiquity. It is often classed as a metalloid, having properties of both metals and nonmetals. Carbon can occur in many different forms, so many that several pages here are dedicated to carbon:
A common form of carbon not listed above is graphite. Graphite forms in sheets, like a stack of paper. Within each sheet, the carbon atom link is very strong. The link between sheets is week, so graphite feels slippery.
Carbon is the basis for life on Earth. A carbon atom can form 4 links with other atoms, and one possibility is a long chain of carbon atoms, written thusly: -C-C-C-C-C- . This leaves 2 links off of each carbon to simple hydrogen atoms or almost anything else. Proteins, polymers, and most of the complicated molecules of life have a backbone of carbon atoms.