Linus Pauling

Linus Carl Pauling was born in Portland, Oregon, on 28 February 1901. His father, a druggist, died when he was nine, leaving the family poor; Pauling worked through school, was refused a high-school diploma for skipping a civics requirement, and entered Oregon Agricultural College anyway. He took his doctorate at Caltech in 1925 and then spent a transformative year in Europe on a Guggenheim fellowship, visiting Sommerfeld in Munich, Bohr in Copenhagen, and Schrödinger in Zurich, at the precise moment quantum mechanics was being written. He returned to Caltech and set about applying it to chemistry.

That programme made him the most influential chemist of the twentieth century. He explained the chemical bond in quantum-mechanical terms — orbital hybridisation, resonance, electronegativity — and gathered it into The Nature of the Chemical Bond (1939), one of the most cited scientific books ever written. He determined the alpha helix and the beta sheet, the two fundamental structures of proteins, in 1951, reasoning from the planarity of the peptide bond while working in bed with a kidney ailment. He identified sickle-cell anaemia as a molecular disease in 1949, founding molecular medicine. He won the 1954 Nobel Prize in Chemistry. He also, famously, got DNA wrong in 1953 — proposing a triple helix with the phosphates inside — months before Watson and Crick got it right.

The ice calculation is a small piece of this and a perfect miniature of how he worked. Giauque's calorimetry had left a stubborn ~3.4 J/(mol·K) discrepancy in ice's entropy that should have been zero. In 1935 Pauling explained it by counting: the oxygens are perfectly ordered but the protons are not, and the Bernal–Fowler ice rules — two hydrogens near each oxygen, two far, one per bond — leave (3/2)^N arrangements standing all the way to absolute zero. So S₀ = R ln(3/2) = 3.37 J/(mol·K). Giauque and Stout measured 3.4 ± 0.2 the following year. Pauling had used an approximation he cheerfully called crude, and it was exactly right.

His second career was political. Horrified by the bomb, he campaigned against atmospheric nuclear testing, was pursued by McCarthy-era investigators, had his passport confiscated in 1952, and in 1958 presented the United Nations with a petition signed by more than 11,000 scientists. The Partial Test Ban Treaty took effect on 10 October 1963 — the day he was awarded the 1962 Nobel Peace Prize, making him the only person ever to receive two unshared Nobel Prizes. His last decades were spent advocating megadose vitamin C, a position the evidence did not support and which cost him much of his late scientific standing. He died in Big Sur, California, on 19 August 1994.