Asked by CHRIS
Who calculated Avogadro’s number?
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Short answer: No single person “calculated” it at the time Avogadro proposed his idea. The constant is named for Amedeo Avogadro (who in 1811 proposed that equal gas volumes contain equal numbers of molecules), but he did not determine the number.
Key historical steps:
- Johann Josef Loschmidt (1865) made the first rough estimate of the number of particles in a given gas volume (the Loschmidt constant, closely related to number density at STP).
- Jean Baptiste Perrin (around 1908–1913) performed Brownian‑motion and sedimentation experiments that gave the first reliable experimental values for Avogadro’s number; Perrin’s work is often credited with settling its value and earned him the Nobel Prize (1926).
- Robert Millikan’s oil‑drop work on the electron charge, combined with the Faraday constant, also provided another route to N_A.
Modern note: since 2019 Avogadro’s constant has been fixed by definition as exactly 6.02214076 × 10^23 mol^-1.
Key historical steps:
- Johann Josef Loschmidt (1865) made the first rough estimate of the number of particles in a given gas volume (the Loschmidt constant, closely related to number density at STP).
- Jean Baptiste Perrin (around 1908–1913) performed Brownian‑motion and sedimentation experiments that gave the first reliable experimental values for Avogadro’s number; Perrin’s work is often credited with settling its value and earned him the Nobel Prize (1926).
- Robert Millikan’s oil‑drop work on the electron charge, combined with the Faraday constant, also provided another route to N_A.
Modern note: since 2019 Avogadro’s constant has been fixed by definition as exactly 6.02214076 × 10^23 mol^-1.
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