The 9 postulates of Dalton's atomic theory

Today we all know that matter is made up of small particles called molecules which in turn are configured by atoms of different elements (which are currently known which are made up of different subatomic particles such as protons, neutrons and electrons).

But although there were already precursors even in ancient Greece, it would not be until 1803 that it would be elaborated at the scientific the theory that matter is made up of basic and indivisible units that come together to form different compounds, considering atoms said indivisible units and compound atoms, or what Avogadro would later call molecules, the compounds formed through them.

That's the Dalton's Atomic Theory, which elaborated different postulates or principles that tried to give an explanation to the configuration of matter.

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John Dalton: Brief Introduction to the Creator of Atomic Theory

The figure of John Dalton is widely known to be the founder of atomic theory

and also for investigating and publicizing the vision alteration known as color blindness, which he also suffered. This scientist was born in Great Britain in 1766, the son of a working family with few resources. Despite the difficulties, Dalton would learn science and mathematics in school and even go so far as to teach at the age of twelve. In time he would open and run a school, along with his brothers.

Later he he expanded his interest to various sciences such as astronomy and geography, coming to give lectures on the matter. He considered studying medicine, but would be put off by his surroundings. He conducted various research and publications in various areas, including meteorology or even grammar. One of the most well known today is the one that has to do with the lack of color perception that he himself suffered and which is currently known as color blindness.

He would also investigate other phenomena such as heat, the behavior of gases and different elements. His work in these last areas would lead him to reflect on the composition of matter, which would end up leading to the development of atomic theory.

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Dalton's Atomic Theory

One of Dalton's most important and recognized contributions to the field of science is his conception of atomic theory. Said theory established a model that tried to explain the behavior of matter as well as the fact that the combination of different proportions of different substances can generate different compounds, explaining the composition of complex elements from different balances of other substances.

The various investigations that Dalton would carry out would lead him to think that all matter is made up of compounds and elements, the former being formed by combinations of the latter. There are a series of indivisible particles, the so-called atoms, that make up the base of the different particles and have different characteristics from each other. Each of the elements is formed from atoms of different kinds. Dalton's theory recovers concepts proper to ancient philosophers, like the concept of atom in the Greek Democritus, but with a somewhat different meaning from the original.

Thus, Dalton did not believe that all matter could be identified with a single substance, but that Atoms of different types and characteristics existed, with weight being one of the most studied variables. In fact, the creator of the atomic theory came to establish a table of elements based on the weight attributed to each of the known types of atoms, such as hydrogen and oxygen (although this initial table was not correct due to the lack of knowledge and difficulty in measuring the weight of the different particles with the techniques of that initial table). epoch). It is also due to him that hydrogen is considered the basic standard when it comes to considering the atomic mass of each element, being the lightest element.

Dalton's postulates

Dalton atomic theory can be summarized based on a series of postulates, which are described below.

1. The matter is made entirely of atoms, units of indivisible matter that can neither be generated nor destroyed.
2. The atoms of a specific element in all cases have the same size, weight and qualities, all of them being equal to each other.
3. The characteristics of the atoms of different elements they are also always different, having different characteristics.
4. While they can combine with other substances to form different compounds, the atoms themselves remain unchanged, not being able to be divided or destroyed.
5. Compounds are formed by combining the atoms of two or more different elements.
6. The combination of different types of atoms is carried out through simple relationships.
7. The combination of two specific elements can give rise to different compounds depending on the proportions in which they are mixed.
8. In chemical reactions it is possible to create, dissociate or transform moleculesThese being a reorganization of the atoms that make up each compound.
9. The same compound is always produced by the same proportion in the combination of atoms.

Some aspects that the most current evidence has contradicted

Dalton's atomic theory has been one of the most important in science when it comes to describing the structure of matter. However, from the time this theory was developed there have been numerous advances that have shown that some of the postulates defended by the author are not true.

For example, the fact that the atom is a basic and indivisible unit has been shown to be false, by being able to distinguish within the atom different parts formed by subatomic structures such as protons, neutrons, and electrons.

The fact that all atoms of the same substance have the same properties has also been uncertain. We can find atoms of different electrical charge according to the balance between protons and electrons (what we know as ions), as well as different atomic masses of the same element (the isotopes).

A third aspect that has been shown to diverge from Dalton's atomic theory is the fact that atoms are unchangeable, which is why has been denied with the advent of nuclear fission and fusion.

Although the evidence has shown that some of the postulates are not entirely true, Dalton's theory has laid the foundations of modern chemistry and has allowed a great advance in the understanding of matter and its behavior.

Bibliographic references:

• Gribbin, J. (2006). History of science: 1543-2001 (2nd edition). Barcelona: Crítica, S.L.

• Petrucci, R.; Harwood, W.; Herring, G. & Madura, J. (2007). General Chemistry. 9th ed. Upper Saddle River, New Jersey: Pearson Prentice Hall.

• Rosental, M. and Iudin, P. (1973). Philosophical Dictionary. Universe Editions.

• Soledad, E. (2010). Chemistry and atomic theory. General chemistry. UNED, 22-23.