Diamond and pencil graphite are the same element: both are pure carbon, element 6. The difference is only how the atoms are joined. In diamond every carbon atom bonds to four others in a rigid three-dimensional network, which makes it the hardest natural material. In graphite each atom bonds to three others in flat sheets that slide over each other, which is why a pencil can write. Carbon can do all this because its atom makes four bonds, and the same four bonds build buckyballs, graphene and the molecules of every living thing, including you.
Element 6. Carbon. The name comes from the Latin carbo, coal. Here is the fact nobody believes: you are carbon too. After oxygen, it is the second most abundant element in your body by mass, about 18 per cent. Almost a fifth of you. One is clear, the other black; one scratches anything, the other leaves a smudge on paper. Same element. Different arrangement.
Why does carbon form four bonds?
A carbon atom has six protons and six electrons. Two electrons sit in an inner shell; the other four sit in the outer shell. An outer shell is most stable with eight, and carbon has only four. Gaining four more, or losing all four, is hard work, so carbon does something more civilised: it shares. Each of its four outer electrons pairs with an electron from a neighbouring atom, and each shared pair is a bond. Four outer electrons, four bonds. Chemists call this tetravalent; it is easier to picture an atom with four hands.
The simplest example is methane, CH4: one carbon holding four hydrogens. The four bonds push apart as far as they can, so they point to the corners of a tetrahedron, about 109.5° apart. In 1874 a young Dutch chemist, Jacobus van ’t Hoff, proposed exactly this, that carbon’s bonds point to the corners of a tetrahedron; in France, Joseph Le Bel came to the same idea independently. In 1901 van ’t Hoff received the very first Nobel Prize in Chemistry, though for other work, on solutions.
Carbon’s real talent is that its hands can hold other carbon atoms, strongly. It builds chains, branches and rings, with single, double and even triple bonds. That is why carbon makes millions of compounds, and why organic chemistry is simply the chemistry of carbon compounds. Join the four hands only to other carbon atoms and you get pure carbon in different forms, which chemists call allotropes.
Diamond and graphite: the same element, arranged differently
For a long time nobody guessed that a diamond and a lump of coal had anything in common. Then, in 1772, the French chemist Antoine Lavoisier focused sunlight through a lens onto a diamond. The diamond burned, and the only product was carbon dioxide. In 1797 the English chemist Smithson Tennant repeated and extended the experiment, and helped prove that diamond is the same substance as charcoal: pure carbon.
So why is diamond so hard? Because every carbon atom uses all four hands. Each grips four other carbon atoms at the corners of a tetrahedron, and the tetrahedra link into a rigid three-dimensional network. Diamond is the hardest natural material and the best natural conductor of heat, yet it conducts electricity poorly.
Graphite uses only three hands. Each atom bonds to three neighbours in flat sheets of hexagons, like a honeycomb. The sheets are stacked with a gap between them and no bonds across it. The fourth electron is free to wander along the sheet, so graphite conducts electricity, and because the sheets are only weakly held together, they slide over one another. That is how a pencil writes: layers of graphite slide off onto the paper.
Centuries ago, unusually pure graphite was found at Borrowdale in northern England, and the locals used it to mark their sheep. People thought it was a kind of lead and called it black lead, or plumbago. Pencil “lead” kept the name, but it has never contained the element lead. In 1789 the German mineralogist Abraham Gottlob Werner named the mineral graphite, from the Greek graphein, to write. Today a pencil core is graphite powder mixed with clay.
Buckyballs and graphene: carbon’s new shapes
For most of history, pure carbon meant graphite or diamond. Then came 1985. The British chemist Harold Kroto was curious about long chains of carbon atoms around carbon-rich stars. In September 1985 he joined Robert Curl and Richard Smalley at Rice University in Houston, and with the graduate students James Heath and Sean O’Brien they vaporised graphite with a laser to see what clusters of carbon would form.
One cluster appeared far more than any other: exactly 60 carbon atoms. Something about 60 was unusually stable. Their answer was a hollow cage with a carbon atom at every corner: 12 pentagons and 20 hexagons, no two pentagons touching, a truncated icosahedron, the pattern of a football. They named it buckminsterfullerene, after the architect Buckminster Fuller, whose geodesic domes share its structure. Their paper, “C60: Buckminsterfullerene”, appeared in Nature on 14 November 1985. Its nickname is the buckyball.
In 1990 Wolfgang Krätschmer and Donald Huffman made it in quantities large enough to study, and the cage was confirmed. In 1996 Curl, Kroto and Smalley shared the Nobel Prize in Chemistry for the discovery of fullerenes. C60 occurs in ordinary soot, and it has been detected in space.
Then a single sheet. One millimetre of graphite is about three million layers stacked together, and one layer on its own, one atom thick, is graphene. In 2004, at the University of Manchester, Andre Geim and Konstantin Novoselov pressed sticky tape onto graphite and peeled it off, ten to twenty times, until the flakes were one atom thick. Many had believed such a thin crystal could not be stable. Graphene is the thinnest material ever made and the strongest; it conducts heat better than any other known material, and not even helium can pass through it. In 2010 Geim and Novoselov won the Nobel Prize in Physics. And every time you write with a pencil, the Nobel committee pointed out, a single layer of graphene may end up on the paper.
Carbon in living things
Take away the water and most of what remains of you is built on carbon. Proteins, fats, sugars and DNA are all built on carbon skeletons, holding hydrogen, oxygen and nitrogen. Glucose, C6H12O6, is built on a chain of six carbon atoms. Life uses carbon for the same reason as the allotropes do: four hands, strong bonds to itself, chains and rings almost without limit.
Where did your carbon come from? Plants pull carbon dioxide out of the air and use sunlight to build sugars; you eat the plants, or animals that ate them. So your carbon was recently in the air. And before that, it was in a star. Almost no carbon was made in the Big Bang. Giant stars make it by the triple-alpha process, in which three helium nuclei fuse into one carbon nucleus. In 1954 the astronomer Fred Hoyle predicted a special state of the carbon nucleus that makes this possible, and experiment later confirmed it.
A porous diamond, made in 2026
The story is not finished. In September 2026 chemists at the University of Gothenburg, with colleagues at Stockholm University and Chalmers University of Technology, reported a new form of carbon called diamondiyne, in the journal Angewandte Chemie. Its carbon atoms form tetrahedra joined corner to corner in all three dimensions, like diamond, but with empty spaces between them, and the researchers compare it to a porous diamond. Theory had described it 35 years earlier.
The structure creates voids between the tetrahedra. The carbon allotrope can therefore be compared to a porous diamond. — Karl Börjesson, University of Gothenburg, 2026
Unlike diamond, it needs no high pressure: it forms as a thin film where two liquids meet. So far it has been confirmed only in patches about 10 nanometres across, and its properties are still to be studied.
Diamond, pencil, buckyball, graphene, a diamond full of holes. And you. One element, four hands, arranged in different ways. For the story of the element that burns all of them, read who discovered oxygen.
Every element has a story. That was carbon’s.
