Carbon: a multitalent

The sparkling diamond on a ring, the grey lead in your pencil and the black charcoal on the barbecue seem to have nothing in common at first glance. And yet the same element is at work in all three: carbon. How can one and the same element look and behave so differently? That is exactly what we are going to explore.

One element, many faces

Carbon has the symbol C and atomic number 6: every carbon atom has 6 protons in its nucleus. In diamond, the atoms are connected in a rigid lattice where each atom is firmly bonded to four neighbours. That makes diamond the hardest natural material we know. In the graphite of your pencil lead, the very same atoms lie in thin layers stacked on top of each other that slide past one another easily. That is why graphite is soft and leaves a trace when you write. And because electrons can move freely within the graphite layers, graphite even conducts electricity. A pencil lead, by the way, is graphite baked together with a little clay: the more clay it holds, the harder and fainter the line.

Same atoms, different arrangement

So the difference between diamond, graphite and charcoal is not in the atoms themselves but only in how they are arranged. These are called different forms of one element, allotropes in technical language. It is like building bricks: from the same bricks you can build a sturdy castle or a wobbly tower. Charcoal, for example barbecue charcoal or the activated carbon in a water filter, consists of rather irregularly arranged carbon atoms with lots of tiny pores.

The backbone of life

Carbon can do even more: each carbon atom can form four bonds and can link up with other carbon atoms into chains and rings. This creates millions of different compounds: sugars, fats, proteins, your DNA, but also petrol and plastics. All life on Earth is built around carbon skeletons. The chemistry of these compounds is so vast that it forms its own field: organic chemistry. In a chemical formula, the small subscript after a symbol tells you how many atoms of that kind sit in one molecule: H₂O consists of two hydrogen atoms and one oxygen atom. If there is no number after a symbol, exactly one atom is meant.