We explain what Dalton’s atomic model is, what its main characteristics are and its limitations.
John Dalton developed the first atomic model in 1803.
What is Dalton’s atomic model?
Dalton’s atomic model was the first conceptualization of the functioning, structure and arrangement of atoms. It was created between 1803 and 1807 by the English scientist John Dalton, who called it “atomic theory” or “atomic postulates” at the time.
This theoretical elaboration made it possible to provide for the first time a satisfactory explanation of both the Law of constant proportions – which establishes the fixed proportionality between substances that react – and the Law of multiple proportions – which states that the proportions between substances that participate in A chemical reaction is always whole numbers. It also made it possible to explain the existence of numerous elemental substances from a finite set of constituent particles.
Dalton’s atomic model is a relatively simple combinatorial model, which It explained almost all the chemistry of the time and that laid the foundations for future developments and innovations in this and many other fields of science.
See also: Bohr Atomic Model
Postulates of the Dalton model
According to Dalton, atoms could not be created or changed in a chemical reaction.
- First postulate. The first postulate of Dalton’s theory established that all matter is made up of elementary particles called “atoms” and that they cannot be divided, nor can they be destroyed. Nor, according to Dalton, can they be created or changed in any chemical reaction.
- Second postulate. The atoms of any element are identical to each other, both in weight and in other characteristics; thus, all oxygen atoms are necessarily identical. On the other hand, the atoms of different elements are distinguished from each other by their weight. From this postulate arose the notion of relative atomic weight, comparing the weight of different atoms with that of hydrogen.
- Third postulate. Atoms cannot be split, regardless of whether they combine as a result of a chemical reaction. The combination of equal or different atoms will generate more complex compounds or substances, but always based on the atom as the minimum fundamental unit of matter.
- Fourth Postulate. The combination of atoms of different elements can form different compounds depending on the quantities of these elements. For example, hydrogen peroxide (H2O2) is composed of two oxygen atoms and two hydrogen atoms, while the water molecule is composed of one oxygen atom and two hydrogen atoms (H2O). In other words, oxygen and hydrogen are present in these two chemical compounds, but in different proportions.
- Fifth postulateAtoms of different elements can combine in quantities of two or more to form different chemical compounds.
- Sixth postulate. Atoms cannot be created or destroyed during a chemical reaction.
- Seventh postulate. When atoms combine to form chemical compounds, they do so in a simple numerical ratio, never fractional.
Virtues of the Dalton model
Dalton’s theory was simple, effective and advanced for its time.
There are many achievements of the Dalton model, which It marked the formal beginning of chemistry as we understand it today.. Atomic theory provided a channel for the chemistry questions of the 18th and 19th centuries, and laid the foundations for the subsequent explosion (in the 20th century) that would lead, hand in hand with technology, to new discoveries in the understanding of subject. Dalton’s theory was simple, effective and advanced for its time.
Limitations of the Dalton model
A major limitation was the lack of knowledge of atomic weights.
It was impossible for Dalton to know in the 19th century what the 20th century would reveal in terms of understanding atoms, such as that they are indeed made up of smaller, electrically charged matter: protons, neutrons and electrons. In fact, advances in atomic energy demonstrated that the atom can indeed fission and fuse.
Another important limitation had to do with the absence of knowledge of atomic weights, as established by the periodic table (later created by Mandeleev and Meyer) and its periodic regularities and specific chemical properties. This limitation was due to the fact that Dalton believed that chemical compounds were formed with the smallest amount of elements possible, that is, that water was made up of one oxygen atom and one hydrogen atom (HO) and not one oxygen atom and two of hydrogen (H2O), as it really is. He, too, could not account for the existence of isotopes.
Finally, Dalton He thought that gases were necessarily composed of simple elements and of the same type of atoms. This led him to contradict Gay-Lussac’s results on volumetric relations, which turned out to be demonstrably true.
Predecessors of the Dalton model
There were similar postulates in ancient times, mainly those of the Greek philosophers Leucippus of Miletus (5th century BC) and his disciple Democritus (5th – 4th century BC), who preferred to think about the relationships of matter from a physics perspective rather than from magic or divine will. However, their atomistic models were not based on scientific observation and experimentation but on logical reasoning.
Another predecessor was The Irishman Higginswho proposed a similar but less successful theory in 1789.
Later models
The indivisibility of the atom was contradicted by the discovery of the electron.
Other atomic models such as Thompson’s (model known as “The Plum Pudding”) They were made possible by Dalton’s postulates, although his indivisibility of the atom was contradicted by the discovery of the electron at the end of the 19th century.
In 1911, Rutherford proposed a model in which the atom is composed of a positively charged nucleus where most of the mass of the atom is, around which negatively charged electrons orbit.
Then, in 1913, Niels Bohr unveiled a model in which electrons orbit a positive nucleus, but they only do so in certain allowed orbits.
These atomic models are followed by more modern models that are more specific and closer to the reality of the atom, but this has been possible thanks to technological advances.
Continue with: Carbon atom
References:
- Chemistry 2. Pascual de Anda Cárdenas, Sandra Jara Castro, Ma. del Refugio Vivas Arceo, Herminia Flores de León and Ma. de los Ángeles Rodríguez Bautista. Threshold Publishing. 2007. ISBN: 978-970-9758-81-8
- Fundamentals of chemistry. Burns, Ralph A. Pearson Education. 2003. ISBN 9789702602811
- On the Structure of the Atom: an Investigation of the Stability and Periods of Oscillation of a number of Corpuscles arranged at equal intervals around the Circumference of a Circle; with Application of the Results to the Theory of Atomic Structure. J. Thomson, FRSPhilosophical Magazine. 1904
- “Atomic model” on Wikipedia.