The notion of the atom as presented by the Greek philosopher Democritus was not shared by many scientists throughout the centuries. But in the year 1804, the dalton Atomic Model, based on the theories of the Greek Atomists, which was accepted.
Dalton's Atomic Model
After the atomistic thought and the Greek philosophical ideas, about 2 thousand years passed until a new atomic theory was made known to the scientific world. Its origin was in the investigations of John Dalton, who was a British physicist, chemist and meteorologist and was the promoter of the first modern atomic theory.
It could be said that Dalton was what was called a complete scientist, because his studies were not limited to physics, on the contrary, he has also been widely recognized for his research on the impossibility of being able to appreciate colors by the human eye, a condition that, thanks to him, today it is known as Daltonism.
His atomic model was known as the billiard ball model and was presented in 1804. Dalton was a scientific researcher and his model was the product he reached after the conclusions that were the result of multiple experiments he carried out. with gases. He was the forerunner of theories such as the Rutherford Atomic Model.
Taking as a basis the conclusions and effects of his work, Dalton was able to prove that the atoms that the Greeks spoke of truly existed, an issue that the Atomic Theory of Democritus he had only sketched, being able to establish the first scientifically based theory of the existence of the atom in the history of modern physics.
Basic Principles of Dalton's Atomic Model
Dalton's atomic model was the first visualized attempt at the mechanism, conformation and location of atoms, conceived between 1803 and 1807, John Dalton first gave it the name of atomic theory and based on it, made the following premises :
first postulate
He determined that all matter is made up of elementary particles, called atoms, and can neither be divided nor destroyed. They also could not be created or changed in a chemical reaction.
second postulate
The atoms that make up any element are identical to each other, not only in weight, but also in other characteristics. Therefore, all oxygen atoms are absolutely equal. Instead, atoms of different elements differ from each other by their weight. Thanks to this postulate, the knowledge of the relative atomic weight arose, through the comparison of different atoms with that of hydrogen, which according to Dalton was the simplest.
third postulate
Atoms cannot be divided, no matter what type of chemical action is performed on them. The combination of the same or different atoms will give rise to more complex compounds or substances, but always starting from the atom as the minimum fundamental unit of matter.
fourth postulate
The combination of atoms with each other, to form compounds, will always reveal a relationship that can be expressed in simple and complete numbers. Never in fractions, since atoms cannot be divided. That is what happens with oxygen, which is formed by two equal atoms (O2), or with water, which are two equal and one different (H2O).
fifth postulate
By combining atoms of random elements in different amounts, numerous different compounds can be formed. This is the only way in which it can be explained that, starting from a finite number of atoms, all the matter in the universe has been built. To exemplify this idea, a carbon atom and two oxygen atoms will form a compound (CO2), but only one of each element will form a different compound (CO).
sixth postulate
All chemical compounds are formed when the atoms of two or more different elements are joined, in a constant and simple way. But, according to Dalton's theory, atoms of the same element do not initially exhibit any affinity for each other, only in the presence of different atoms.
Dalton's Laws
As a consequence of these postulates, the following laws were formulated:
- All matter is made up of atoms.
- Absolutely everything that is known is made up of atoms, both on earth and in the known universe. Each of the elements is made up of atoms.
- Atoms are indivisible and indestructible.
- Atoms are the smallest particles of matter.
- All atoms of a given element are identical.
- In a specific element, all its atoms have the same mass and the same characteristics.
- Atoms of different elements vary in mass and properties.
- Each element is made up of atoms of different characteristics and mass.
- Compounds are made up of a combination of two or more different kinds of atoms.
- A specific compound always has the same kinds of atoms combined and in the same proportions.
- A chemical reaction is a rearrangement of atoms.
- Chemical reactions are the product of a separation, union or rearrangement of atoms. But, atoms of one element never become atoms of another element as a result of a chemical reaction.
Additional considerations of the Dalton Atomic Model
Along with the creation of the basic principles listed above, Dalton proposed that the atoms of two elements that are related to each other to form molecules respect the Law of Conservation of Mass. This means that the number and types of atoms found in a molecule are the same as the number and types of atoms of the elements used in the chemical reaction.
Another relevant statement of this theory was the Law of Multiple Proportions, according to which when two atoms of two elements are conjugated, the conjugation can only occur according to a ratio of whole numbers such as 1:1, 2:1, 2:2 , and so on. If water is taken as an example, it can be seen that H2O combines in the ratio 2:1, which means that it has two hydrogen atoms and one oxygen.
Therefore, it is not possible that a different proportion of these elements can be used to produce water. It is not possible to produce water using 3 hydrogen atoms and two oxygen atoms (3:2).
Dalton was also able to create a "Table of Atomic Weights" and using the data from that table, he was able to place the elements in an arrangement determined by the weight of their elements, from a comparison with hydrogen, which is the lightest element, which is the first in your table and has the atomic number of 1.
The billiard ball model
A consequence of having the idea that atoms were the smallest particles of matter was to be able to imagine them as solid and hard spheres, for which many of his representations were made with models made with wooden spheres, thanks to which he received the billiard ball model name.
The chain of reasoning of Dalton's theory was able to explain in a scientifically satisfactory way two laws: the Law of constant proportions, according to which proportionality is fixed between reacting substances, and the Law of multiple proportions, according to which the proportions between reacting substances will always do so in whole numbers.
Through this formulation it was also possible to explain the existence of numerous elementary substances, starting from a finite set of constituent particles. It was later improved with Rutherford's theory and the Bohr Atomic Model
Dalton's atomic model is an essentially simple combinatorial model, which could give an elucidation to almost all the chemistry of his time and with it the foundation for the development and future innovations in the field of chemistry and in various other fields of science.
Dalton's Experiments
Contrary to the Atomists, who only used their logic to conceptualize the atom, Dalton based his assertions on a large number of experiments that proved the existence of atoms, carried out entirely from the perspective of chemistry. Several of the best known were:
He carried out experiments with matter in a gaseous state, observing the effects of the pressure of that state of matter, arriving at the conclusion that the atoms of which gaseous matters are composed are in an uninterrupted fortuitous movement.
Some of his experiments were based on a mixture of elements to make molecules of compounds, the results of which allowed him to assert that a given compound will always be made up of the same elements in the same proportions and following his Law of Multiple Proportions.
Acceptance of the Dalton Atomic Model
Dalton's atomic theory was widely accepted by many scientists of his time without much time being required for it and became the basis for some sections of today's atomic theory.
Although today scientists also know that atoms are not the smallest particles of matter, since, as is known, atoms contain several kinds of smaller particles, such as protons, neutrons and electrons. Dalton's theory was immediately established as the theoretical basis for chemistry.
Limitations and Errors in Dalton's Theory
Dalton had the hypothesis that the atoms of all the elements remained individual, due to which he was not able to realize that in some elements the atoms exist in molecules, as is the case of pure oxygen that exists as O2, that is that is, a molecule of the same element with two oxygen atoms.
Likewise, his idea that the simplest compound between two elements is constantly one atom of each was wrong. Error that led him to deduce that the expression for water was HO instead of H2O.
The fact that the equipment he used to do his experiments was very basic led Dalton to several wrong conclusions. In his early days he gave oxygen a value of 5.5, which means that it was 5.5 times more voluminous than the hydrogen atom, which was the one he used as his reference. However, he was able to correct those values years later, giving oxygen a value of 7, despite the fact that other researchers of his time gave oxygen a value of 8.
Impact of Dalton's Theory
It is true that current atomic theory has reached levels that were indescribable a few years ago, but Dalton's genius is that the essential principles of his theory are still valid in certain respects. However, today it is known that atoms can be separated by means of reactions at the nuclear level, but this does not mean that Dalton's statement that they cannot be separated by means of chemical reactions is no longer valid.
In addition, today it is also known that not all atoms of the same element have the same mass, since it has been possible to demonstrate that isotopes exist, which are atoms with additional neutrons, and that they have a greater mass even when it is the same. element.
Dalton's Biography
John Dalton was born in England on September 6, 1766, his family was humble and his early education was from his parents and from a school in his town. Due to his origins and the economic condition of his family, he had to start working at the age of 10, serving in a house, although it is also stated that he began teaching at a school at the age of 12 and that at 14 became proficient in Latin.
Dalton continued to teach and receive informal instruction from instructors in the area in which he lived, and when he reached the age of 27 he received an appointment as professor of mathematics and natural philosophy at a small university in Manchester, a position in which he continued for several years. 7 years, until I make the decision to become a private tutor for those same subjects.
Scientific Contributions
Undoubtedly, among his most relevant contributions is his theory of the Atom, but John Dalton conducted studies and experiments on:
- Meteorology.
- Measurements of the heights of mountains.
- Color blindness, a condition that was later named Daltonism in his honor.
- Some Laws related to gases.
And he made many other publications of his works on minor subjects, such as that related to the color of the sky and even on English grammar.
Dalton was a man of reserved character and never married. He dedicated himself exclusively to his investigations, he had a modest life and without much fuss. In the years 1837 and 1838 he suffered from seizures which resulted in his becoming mute, but this did not prevent him from further investigation, until the year of his death, in 1844.