Amedeo Avogadro

Physicist and chemist — Amedeo Avogadro, Count of Quaregna (Turin 1776 – Turin 1856), was an Italian physicist and chemist who graduated in law before devoting himself to science. In 1811 he formulated the famous hypothesis that equal volumes of different gases, under the same conditions of temperature and pressure, contain the same number of particles. He also introduced the concept of the molecule, distinguishing it from the atom, clarifying the composition of gases such as hydrogen and oxygen. This insight was fundamental in establishing atomic and molecular weights and for the birth of modern chemistry. In his honour, the constant indicating the number of particles in a mole bears his name.

Trivia

His hypothesis was ignored for almost half a century and was recognised only after his death, when Stanislao Cannizzaro put it forward again at the Karlsruhe Congress of 1860.

Theories and contributions

• Avogadro’s law — Equal volumes of gases under the same conditions contain the same number of molecules: $V \propto n$ at constant $T$ and $p$.
• Avogadro’s number — Number of entities in a mole: $N_A \approx 6{,}022\times10^{23}\ \text{mol}^{-1}$.

Present in chapters

00 00a 09

Linked atoms

5 linked atoms.

00 Grandezze fisiche, stime, equilibrio

• What is a physical quantity

00a Come usare il libro

• Quick reference

09 Teoria cinetica dei gas

• Internal energy of an ideal gas
• Atoms: from philosophical hypothesis to experimental evidence
• The Van der Waals equation