1 jan 1803 ano - John Dalton
Descrição:
Although Democritus proposed the existence of the atoms, John Dalton was the first to truly put the atom on a solid base to evolve off of. In fact, most of Dalton's "Atomic theory" is still inherently true today, making it extremely important. However, the actual atomic model di not really change in the two millennia between Dalton and Democritus.
His Atomic theory provides a precise definition about atoms and their properties. These are summed up as:
- Elements are composed of extremely small particles called atoms
- All atoms of a given element are identical: e.g same size, mass, and chemical properties.
-Atoms of different elements have a different size, mass and chemical properties.
-Atoms are not created or destroyed into different types during a chemical reaction. This later became the Law of Conservation of mass.
-A chemical reaction involves only separation, combination or a rearrangement of atoms.
- Some Compounds are formed when atoms of more than one element combine in a specific ratio, even if they share the same common element or group of elements. E.g Water= 2:1 hydrogen to oxygen ratio, Carbon dioxide= 2:1 Oxygen to carbon ratio.
The atomic theory, especially the parts about compounds and the laws for conservation of mass was based on experiments with gases only just becoming possible in the turn of the 19th century such as pure hydrogen and oxygen. By doing several of these experiments he discovered that every time water was produced from H and O, they would always form in the ratio of 2:1.
(image at top) John Dalton self-portrait
(image at middle) John Dalton's atomic model
(Image down bottom) The experiment results of Dalton's experiments with hydrogen and oxygen gases.
References:
-Williams, M., & Williams, M. (2018). What Is John Dalton's Atomic Model? - Universe Today. Universe Today. Retrieved 12 February 2018, from https://www.universetoday.com/38169/john-daltons-atomic-model/
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Adicionado na linha do tempo:
History of the atom
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