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For most of the twentieth century, pure carbon meant diamond or graphite. Then, in a Texas laboratory in 1985, a cluster of exactly 60 carbon atoms kept turning up in an experiment that was meant to be about stars. This post covers who the three chemists were, how they reasoned their way to a hollow carbon cage, a worked count you can do with Class 9 geometry, and what their way of working can teach you.
Who were Kroto, Curl and Smalley?
Harold Kroto was born on 7 October 1939 in Wisbech, England, and died on 30 April 2016, according to his Nobel Prize facts page. He worked at the University of Sussex. Richard Smalley was born on 6 June 1943 in Akron, Ohio, and died on 28 October 2005 (facts page). Robert Curl was born on 23 August 1933 in Alice, Texas, and died on 3 July 2022 (facts page). Curl and Smalley were at Rice University in Houston. The three shared the 1996 Nobel Prize in Chemistry "for their discovery of fullerenes".
Why was a scientist who studied stars working in Texas?
The Nobel press release explains the unlikely meeting. Kroto used microwave spectroscopy to study molecules in space. He had found long chains of carbon and nitrogen, called cyanopolyynes, in carbon-rich giant stars and in interstellar gas clouds, and he suspected they formed in the hot atmospheres of stars.
Smalley had built a laser-supersonic cluster beam apparatus that could vaporise almost any material and let him study the clusters of atoms that formed as the vapour cooled. Curl, a spectroscopist who often worked with Smalley, told him about Kroto's interest. On 1 September 1985 Kroto arrived at Smalley's laboratory to vaporise carbon.
What did the experiment actually show?
A pulse of laser light hit a graphite surface. The carbon atoms released were swept along by helium gas, cooled as the gas expanded into a vacuum, and sorted by mass in a mass spectrometer. Working with graduate students J. R. Heath and S. C. O'Brien over eleven days, the team found that one peak could be made to dominate the others: clusters of 60 carbon atoms, with a smaller peak at 70.
Why would 60 be special? The group proposed a closed, hollow cage shaped like a truncated icosahedron. Their paper, C60: Buckminsterfullerene, was sent to Nature on 12 September and published on 14 November 1985. Its abstract describes a shape with 60 corners and 32 faces, 12 of them pentagons and 20 hexagons, "commonly encountered as the football". The name honours the architect Buckminster Fuller, whose geodesic domes have the same kind of structure.
How was a molecule nobody could see confirmed?
The press release says the proposal had a mixed reception, ranging from criticism to enthusiasm. Between 1985 and 1990 the team gathered more evidence. If the cage was hollow, it should be able to hold an atom inside. Graphite soaked in a lanthanum salt gave clusters containing a lanthanum atom that a laser could not knock out, which fits an atom trapped in a cage.
The decisive step came from physicists. In 1990 Wolfgang Krätschmer, Donald Huffman and colleagues reported in Solid C60: a new form of carbon that an arc between graphite rods in helium produces soot from which C60 can be extracted with an organic solvent in isolable quantities. With a real sample in hand, the full set of structure methods could be used, and the football shape was confirmed.
Worked example: counting C60's atoms, bonds and faces
The Nature abstract gives three facts: 60 carbon atoms at the corners, 32 faces (12 pentagons and 20 hexagons), and each carbon joined by two single bonds and one double bond. Check that they fit together.
Bonds. Each carbon has three neighbours. Counting 60 × 3 = 180 counts every bond twice, once from each end, so there are 180 ÷ 2 = 90 carbon-carbon bonds.
Euler's rule. For any convex polyhedron, corners minus edges plus faces equals 2. Here 60 − 90 + 32 = 2. It works.
Corners from faces. The pentagons have 12 × 5 = 60 corners in total, and every carbon sits on exactly one pentagon. The hexagons have 20 × 6 = 120 corners, so every carbon sits on two hexagons.
Double bonds. Each carbon has one double bond, and each double bond joins two carbons, so there are 60 ÷ 2 = 30 double bonds and 90 − 30 = 60 single bonds.
Bigger cages. The press release notes that a closed cage with n carbons (n even and above 22) can be built from 12 pentagons and (n − 20) ÷ 2 hexagons. For C70 that gives (70 − 20) ÷ 2 = 25 hexagons.
Common mistakes:
Forgetting to halve. Multiplying atoms by neighbours counts each bond twice. The same trap appears in counting edges of any solid.
Assuming hexagons alone can close a ball. They cannot. A flat sheet of hexagons is graphite; the 12 pentagons are what curve it shut.
Calling C60 a giant network like diamond. The press release stresses that fullerenes, unlike the other forms of carbon, are well-defined molecules.
What can a student take from how they worked?
They followed an anomaly. The experiment was about long carbon chains, but the result that mattered was a peak nobody expected. They also combined fields: astrochemistry, laser cluster physics and spectroscopy each held part of the answer. Finally, they checked their idea with simple counting and with predictions that could fail. You can do the same with a new structure in your textbook: count atoms, bonds and faces, and see whether the numbers agree.
Fullerenes are one of several unusual forms of carbon. For a flat one, read about Andre Geim and graphene; for a rolled one, see Sumio Iijima and carbon nanotubes. If ideas such as allotropes or aromatic rings still feel shaky, the Fermi Concept Library covers every concept in physics, chemistry, biology, mathematics and computing, so you can look one up when you meet it.
Try it now: count the corners, edges and faces of a cube and a football, and check Euler's rule for both.
