Advances in the atomic-molecular theory

The constitution of the atom

The dawn of the mole concept

First estimation of the molecular dimensions First determination of the molar gas constant R

First determinations of Planck (h), Boltzmann (KB), and Avogadro (NA) constants

The electron The proton The isotopes The neutron

Giuliano Moretti, CnS La Chimica nella Scuola, N.5, pp. 13-27, 2016

The H atom

Richter (1792) and Wallaston (1814)

Concept of chemical equivalencyEquivalent weights of acids and bases

Dalton (1803 - 1808)

“Atomic” (Equivalent)weights, rule of simplicity

Avogadro (1811)

Equal V equal number ofmolecules (p, T)

Dulong and Petit (1814)

In solid substancesCa ≈ 6 cal gram-atom-1 °C-1

Faraday (1834)

Laws of electrolysis

Cannizzaro (1858)

Avogadro’s principle and law of atoms(corrected atomic weights and formulas)

Mendeleev (1869)

The Periodic Table

Loschmidt (1865)

Kinetic theory of gases

Horstmann (1873)

P(V/n) = RT(V/n = molar volume)

van der Waals (1873)

[P+a/(V/n)2][(V/n)-b]=RT

Planck (1901)Black body radiation:h and KB then NA=KB/R(Idea of the quantum)

Einstein (1905)Brownian movement andother methods tocalculate NA (and ma(H))

Millikan (1909)Electron charge andFaraday’s constant:NA= F/e

Perrin (1909)NA by verification of the Einstein’sequation on the Brownian movementand other methods; book Les Atoms, 1913

Thomson (1896)Determination ofe/m(e) and e/ma(H)(ma(H) = 1700 m(e))

Rutherford (1908) and Moseley (1913)

Radioactivity and the conceptof atomic number

Soddy (1913) and Aston (1919)

Existence of isotopes formost of the elements

Bohr (1913)

The first quantummodel of the atom

Chadwick (1932)

The neutron and itsproperties (m(n) ≈ ma(H))