Diamonds. Charcoal. Plastic. Petrolium. A human.
What do they all have in common? They are all carbon-based. Not counting the water in our bodies, two thirds of our weight comes from carbon atoms. And if you look around... ... you'll find that carbon is the basis for countless substances.
What's so special about carbon? We'll start, as we usually do in chemistry - by looking at the atoms. A carbon atom has six electrons. Four of them are located in the outer electron shell. To an atom, it's always desirable to have eight electrons in the outer shell.
Carbon wants to get four more electrons, from other atoms. It's as if carbon has four arms, that are able to hold on to other atoms. Four possible bonds is more than the other common elements found in nature have. This makes carbon versatile - it can form millions of different compounds. On its own, carbon comes in different forms.
Such as diamond. A diamond is entirely made up of carbon atoms. Each carbon atom is bonded to four other carbon atoms. All the atoms hold on to each other. This makes diamond a very strong and hard material.
The strongest that exists in nature. All the outer electrons are locked in chemical bonds. No electrons are free to move. Diamond doesn't conduct electricity at all. But carbon atoms are not always bonded that hard in all directions.
This is graphite. It is also a form of pure carbon. Here the carbon atoms form layers. Each one with a hexagonal pattern, like in a honeycomb. Each carbon atom is only bonded to three other carbon atoms, leaving one electron from each atom free to move: Graphite conducts electricity.
Each atom layer has strong bonds within itself, but the different layers are held together by weak attractive forces. They slide easily off one another, which makes graphite a soft and malleable material. Graphite mixed with clay is the material used in pencils. When you write with a pencil, the actual writing is formed by layers of graphite that are smeared out on the paper. If you could peel off only one layer of graphite, you would get a sheet of graphene.
It is only one atomic layer in thickness, which means it is very light. But also very strong. Graphene might be used in touch-screens in the future. Or as a building material. There is one more form of pure carbon.
It has molecules with around sixty carbon atoms in a ball-shape. These round molecules are called Fullerenes. They can be found in soot particles, for instance from candles. Diamond, graphite, graphene and fullerene are all pure forms of carbon. What makes carbon so special is the ability to form different compounds - millions of them.
The reason why so many combinations are possible, is the high number of possible bonds for each atom - four of them.