Molecular hypothesis

molecular hypothesis
An 1894 synopsis of the molecular hypothesis, by American engineer Allan Risteen, according to which mass of matter is composed of separate particles, which largely tend to be molecules (very few individual unattached atoms are found in nature). [3]
In chemistry, molecular hypothesis, sometimes called "Avogadro's hypothesis", states that equal volumes of all gases at the same temperature and pressure contain the same number of molecules; in a more general sense: that all bodies are composed of individual atoms and or molecules.

History
This molecular hypothesis was stated in 1811 by Italian chemist Amedeo Avogadro who, in his use of the term ‘molecule’, distinguish between atoms and molecules of different kinds, adopted terms including molécule intégrante (the molecule of a compound), molécule constituante (the molecule of an element), and molécule élémentaire (atom). [1]

Avogadro’s hypothesis was quickly opposed by John Dalton and its universal validity was later questioned by Jacob Berzelius. It would not be until the start of the 20th century that it became universally accepted and the “touchstone upon which atomic weights and formula are tested”. [2]

See also
Atomic theory
Human molecular hypothesis

References
1. Amedeo Avogadro – Britannica.
2. McCoy, Herbert N. (1908). “The Experimental Basis of Chemical Formulae and the Teaching of the Atomic-Molecular Hypothesis”, School Science and Mathematics, 8(6):441-., Jun.
3. Risteen, Allan D. (1896). Molecules and the Molecular Theory of Matter. Ginn & Co.

Further reading

● Morselli, Mario. (1984). Amedeo Avogadro: a Scientific Biography (§4: “The Molecular Hypothesis: from 1811 to Canizzaro’s ‘Sunto’ in 1858”, pgs. 131-). Springer.

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