Introduction to Carbon

The coal that burns in a stove, the soot that collects on the bottom of a cooking pot and the charcoal made by charring wood are all things we see around the house. All three have the same colour, a deep black, and all three leave a black stain on the finger that touches them. This is not a coincidence. Coal, soot and charcoal are all made of carbon, and that is why they are black. Three things found in three different places are pointing us towards one single element.

Burning things tell the same story. Firewood gives off black smoke as it burns. A burning candle sends up a plume of black smoke. Sugar left on heat chars into a black lump. Smoke, soot and char: where does all this black material come from? Every one of these examples raises the same question: what is this black substance, and where is it hiding?

The word carbon comes from Latin, where it means charcoal. The name itself points at the element's most familiar form. Carbon is generally black in colour and it burns easily in air. It is not a metal; it is a non-metal. People today make heavy use of diamond, graphite and other materials that are built of carbon and nothing else. Carbon is also the main element of every organic compound, which is why it is so widely studied and so widely used.

When carbon burns, it gives off a black plume or black smoke along with heat and light. This behaviour hands us a simple way of testing whether a substance contains carbon. If an object gives off a black plume or black smoke while burning, and the solid left behind after burning is black, then we know that the substance contains carbon. The black smoke of firewood, the sooty plume of a candle and the black char of overheated sugar are all examples of this one rule.

In some places carbon is found on its own, as the pure element, not joined to any other element. Coal, soot and charcoal are the most familiar examples. The lead inside a pencil and the black rod inside a dry cell are also made of carbon. Diamond, graphite and graphene are likewise materials built of carbon and nothing else. Although they are all one element, these materials look and behave very differently: charcoal cooks food, graphite writes in a pencil, and diamond sparkles in jewellery.

The body of every kind of living creature contains carbon in the form of many different compounds. That is why carbon is called the basis of the structure of living things. Carbon does not stop at living bodies either. The food we eat, the clothes we wear, and the tables, chairs, pens and pencils we use all contain carbon compounds. From the moment we wake to the moment we sleep, most of the things we touch carry carbon in one form or another.

The sources of carbon can be sorted into two main groups. First come the sources where carbon exists as the pure element. Second come the sources where carbon has combined with other elements to form compounds. The compounds themselves fall into two families: inorganic compounds and organic compounds.

As inorganic compounds, carbon is found in carbonates, bicarbonates and carbides, in minerals and rocks, and in gases such as CO₂ and CO. As organic compounds, carbon sits inside countless things of daily life: the carbohydrates and proteins in food, fatty substances such as oil and ghee, petrol, urea, vitamins, medicines, and even silk, paper and soap. Gases such as methane, ethane and LPG are organic compounds too. The table below gathers these sources in one place:

That wood and sugar contain carbon is something the eyes can confirm. Burning a piece of wood leaves behind black charcoal. Put a little sugar in a spoon and heat it, and the sugar first melts, its colour turning a golden brown. At this point a sweet smell begins to rise. Keep heating, and the sugar chars completely black, leaving only a substance with an unpleasant smell. That black material, born out of white sugar, is the carbon that was hiding inside the sugar all along. In this way it is confirmed that both wood and sugar contain carbon.