History of atomic theory

The development of ideas about atoms, from ancient philosophical proposals to modern models grounded in experimental evidence.

Leucippus: An ancient Greek philosopher traditionally credited with founding atomism alongside Democritus. He is associated with the earliest Greek proposal that matter consists of indivisible particles.
Dalton's atomic theory: John Dalton's early nineteenth-century theory that chemical elements consist of characteristic atoms combining in fixed ratios. It connected atomic ideas to quantitative laws of chemical combination.
John Dalton: An English chemist and physicist who formulated an influential atomic theory in the early nineteenth century. His chemical laws gave atoms a systematic role in explaining combination and composition.
Plum pudding model: J. J. Thomson's model of an atom as electrons embedded in a diffuse sphere of positive charge. Rutherford's scattering results contradicted its prediction that large deflections were rare.
Periodic table: An arrangement of chemical elements by atomic number and recurring chemical properties. Atomic number revealed the organizing principle behind the periodic pattern of elements.
Democritus: An ancient Greek philosopher who described reality as atoms moving through the void. His account made atomism the most influential ancient alternative to continuous matter.
Avogadro's law: The principle that equal gas volumes at equal temperature and pressure contain equal numbers of molecules. It helped distinguish atoms from molecules and resolve apparent conflicts in chemical formulas.
Amedeo Avogadro: An Italian scientist who distinguished molecules from atoms in a hypothesis about gases. His proposal clarified how gaseous volumes relate to molecular and atomic counts.
Rutherford model: A model of the atom with a tiny, positively charged nucleus surrounded by electrons. Its classical orbiting electrons could not explain atomic stability or line spectra.
Isotopes: Atoms of the same element with equal proton counts but different neutron counts. Their discovery showed that atoms of one element need not all have identical mass.

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