We explain who John Dalton was, what his main scientific contributions were and the importance of the atomic model he proposed at the beginning of the 19th century.
John Dalton was the creator of the first scientific atomic model in history.
Who was John Dalton?
John Dalton was a British chemist, mathematician and naturalistfamous for having proposed the first scientific atomic theory and the first scientific atomic model in history, and for having described color blindness, a genetic condition that prevents the correct perception of colors.
Considered a pioneer in the study of atoms and matter, since the bulk of his studies had to do with physics and chemistry, Dalton was also interested in meteorology, English grammar, optics and geography.. He was the author of various scientific treatises and was a teacher of other important physicists and chemists, such as the Englishman James Prescott Joule (1818-1889).
Dalton was a Researcher and Professor at the University of Oxfordand also an active member of the main scientific societies of Europe. His experiences in the study of matter earned him the respect of his contemporaries and secured him an important place in the history of science.
Birth and youth of John Dalton
John Dalton was born on September 6, 1766 in the town of Eaglesfield, Cumberland, England.His parents were Joseph Dalton and Deborah Greenup, a Quaker couple dedicated to manual labor, of whose five children only three survived to adulthood: Jonathan, John and Mary.
John’s formal teaching began at a Quaker school in Eaglesfield, where he soon demonstrated his talent for learning. So much so that, at the age of twelve, he assisted his older brother in running a school in the town of Kendal, where his cousin George Bewley attended to around 60 students.
At Kendal, John’s scientific interest took its first steps. There he became acquainted with Elihu Robinson, a Quaker teacher and amateur meteorologist, and John Gough, a mathematician and teacher of classics. With them he learned Latin, Greek, mathematics and some basics of meteorology, which were key in the formation of his scientific mentality..
The Quakers quakers, “shakers”), also called “friends”, are a Christian religious community founded in England in the 17th century, whose formal name is the Religious Society of Friends or Church of Friends. Quakers are a dissident group from Protestantism and are governed by their own religious codes and their own interpretations of the Bible.
John was in Kendal until 1793, when at the age of 27 he decided to move to the city of Manchester to continue his academic training.. Thanks to Gough’s intermediation, he was accepted as a teacher of mathematics and natural philosophy at a school for religious dissidents, who at that time were not accepted in regular institutions. He remained there until the closing of the school in 1800.
The discovery of color blindness
In Manchester, John Dalton was able to indulge his passion for knowledge. Shortly after his arrival, his first publication appeared, Observations and meteorological tests (1793), which was largely ignored by the scientific community.
This, however, served to present himself in 1794 before the Philosophical and Literary Society of Manchester and present a work entitled Extraordinary facts related to color visionThere he detailed some of his theories about a phenomenon he had observed firsthand: the discrepancy in the perception of colors, which he attributed to a difference in the constitution of the vitreous humor.
It is said, in fact, that John went to visit his family home in 1792 and gave his mother some deep purple stockings. This color was inappropriate for a puritan woman of her confession, so she was surprised and asked her son what the color was due to. It was then that Dalton noticed that people perceived colors in a different way than he could..
Surprised by the discovery, John undertook an experiment: he observed a geranium flower during the day and took note of its color. He waited until nightfall and returned to the flower by candlelight, and observed that its color changed significantly. He repeated the experiment in the company of different friends and family and noticed that no one else noticed the change in colors, except for his older brother. He then concluded that there was some defect in the family in the ability to perceive colors..
Already in Manchester, Dalton began to become interested in botany, and therefore had the opportunity to continue studying the perception of colors. This is how he noticed that changes in perception occurred only in a range of colors: reds, blues, crimsons or purples.
These studies by Dalton on his vision difficulties allowed him in 1808 to formulate the scientific description of what is known today, in his honour, as “colour blindness”, but which at the time did not obtain the support and credibility of the medical and scientific community. For this reason, Dalton left in writing that he was donating his eyes to science, so that they could be studied in depth and the truth of his partial color blindness would be known..
Dalton’s scientific career
Dalton was admitted to the Manchester Literary and Philosophical Society in 1800.
Dalton’s entry into the Manchester Literary and Philosophical Society finally occurred in 1800, and The following year he gave a series of lectures entitled “Experimental Essays,” in which he presented his research on the nature of gases..
In these lectures, which were published as articles in 1802, Dalton investigated the pressure of water vapor, thermal expansion, and other behaviors of gases subjected to certain conditions of pressure and temperature. Among his experimental conclusions, Dalton stated that, for example, all fluids presented an equivalent vapor pressure variation.
These conclusions also allowed him to resume his atmospheric studies, from which he obtained important conclusions about the constitution and behavior of the atmosphere. As a result, Dalton is also considered the father of meteorology..
However, Dalton’s greatest scientific contribution was his atomic theory and the atomic model that follows from it.It is unknown exactly how Dalton arrived at the ideas that underpin his atomic theory, since his notes on the subject are incomplete.
Dalton’s conclusions about the behavior of gases were based on the idea that atoms repel or tolerate each other under specific physical conditions: he thought, for example, that the atoms in a mixture of gases must repel each other. These conclusions turned out to be false, but they allowed him to understand that the total pressure exerted by a mixture of gases is equivalent to the sum of the pressures of each of its components..
Thanks to this, in 1803, Dalton was able to formulate his Law of Multiple Proportions, known today as “Dalton’s Law”. Demonstrated by the French physicist Louis Joseph Gay-Lussac (1778-1850), this law states that:
When two or more elements combine to give more than one compound, a variable mass of one of them joins a fixed mass of the other and the former has canonical and indistinct numbers as a relationship.
This means that when two elements come together to produce a compound, their combination occurs according to a fixed quantity expressible in whole numbers.Thus, if a compound is formed by elements A and B, the proportion in which they combine will be 1:1 (A:B), 1:2 (A:2B), 2:1 (2A:B), and so on.
Although this law was demonstrated at the time, the reason for its existence was a mystery. To understand it, an atomic theory was needed, something Dalton worked on between 1803 and 1808.
The existence of atoms was already known, since the first hypotheses in this regard date back to ancient times. The Greek philosopher Democritus of Abdera (c. 460 BC-c. 370 BC) was the first to think of the universe as a combination of atoms and vacuum. However, it was Dalton who was the first to scientifically formulate the nature of these atoms.
John Dalton’s atomic theory
Dalton’s model was the first scientific formulation on the nature of atoms.
Once the Law of Multiple Proportions had been demonstrated, Dalton wanted to go a step further and not only know what the proportion of an element was within a given compound, but also how the quantity of elements present in a sample of the compound could be calculated. That is, how much of one element or another is in a compound.
Dalton assumed that this quantity should also be expressible in a simple way. For example, he assumed that methane (CH4), composed of carbon and hydrogen, should have one carbon atom and two hydrogen atoms, and that ethylene (C2H4) should therefore have one carbon atom and one hydrogen atom. These estimates are now known to be incorrect, but Dalton’s basic approach was revolutionary. And, moreover, many of his other deductions were correct.
From there, in 1803 Dalton formulated the first table of relative atomic weights in history, composed of six elements: hydrogen, oxygen, nitrogen, carbon, sulfur and phosphorus. In it he did not explain how he had reached his estimates, but it is known that he deduced them from the study of different substances, such as water, ammonia and carbon dioxide.
The atomic theory developed by Dalton from these foundations appeared in 1808, in his work A new system of chemical philosophy. There he formulated his atomic theory and developed his atomic model, which was tremendously innovative for the science of the time. His atomic theory can be summarized in the following postulates:
- All matter is composed of tiny, invisible, indestructible particles called “atoms.”
- All atoms of a given element are identical to each other.
- The atoms of an element are different from the atoms of other elements, and can be distinguished from each other by their relative atomic weights.
- Atoms of one element combine with atoms of another to form a compound. A given compound is always made up of the same proportion of atoms of its given elements, which can be expressed in simple terms.
- Atoms cannot be created or destroyed in a chemical reaction, nor can they be broken into smaller particles. The transformation of one compound into another through a chemical reaction consists of a rearrangement of its atoms.
This theory was extremely innovative for its time, especially because it was thought that atoms were all identical to each other,…