Re: What is Carbon exactly ?

That's a new one on me. I've never heard carbon called a metal. Typically it is called either a non-metal or a metalloid.

Let's look at definitions.

Metals

My copy of Encarta^TM says they are a group of chemical elements that exhibit all or most of the following physical qualities: they are solid at ordinary temperatures; opaque, except in extremely thin films; good electrical and thermal conductors; lustrous when polished; and have a crystalline structure when in the solid state. My copy of the Oxford Concise Dictionary of Chemistry adds that metals typically form positive ions.

Non-Metals

The Concise Dictionary of Chemistry says that these are elements which typically form anions or covalent compounds. They are poor conductors of heat and electricity.

Semi-metals or Metalloids

These are typically defined as having properties which are intermediate between those of metals and non-metals. This is really an awfully fuzzy definition, but then the whole concept of a semi-metal is awfully fuzzy. Usually, the operational definition is a bit circular: metalloids have semi-conducting properties, so whatever is a semiconductor is therefore a metalloid.

I've always thought of carbon as a non-metal. However, apparently even diamond is a semiconductor -- which is something we expect of metalloids. Graphite is certainly able to conduct electricity -- though not as well as a metal -- because of its electronic structure. And the newest allotropes of carbon, fullerenes (this page is also good), are definitely semiconductors.

Based on the electrical properties, I would classify carbon as a metalloid; traditionally, though, it has been classed as a non-metal. Anyone telling you carbon is a metal is simply wrong.