John Dalton: Atomic Theory, Model, Experiments, and Discoveries

The history of modern atomic theory begins with an unexpected person, a young school principal, and a member of the Quaker cult named John Dalton. In his article for the Manchester Literary and Philosophical Society in 1803, Dalton presented the relative atomic weights of some of the most important chemical elements known to that day. Within a decade, many leading chemists adopted Dalton’s atomic theory in one way or another, and within a generation, chemistry was all about atoms.

Dalton’s father was Cockermouth, a poor weaver who lived in Cumberland, on the northwest tip of England. He spent his first years working on the family’s small farm, but on the other hand, he had a passion for education and became self-educated with the help of local elite Quakers. Even among their peers, the Cumberland Quakers stood out for the importance they placed on education and mental pursuits. Dalton started teaching at the village school at the age of 12. Three years later, he joined his older brother, who runs a boarding school in the nearby town of Kendal. In his spare time, he continued his education by studying classical and modern languages, mathematics, and the natural sciences.

John Dalton’s favorite pursuit at that time was meteorology; he specialized in this field later and continued his research with passion until the end of his life. In 1793, his first book, Meteorological Observations and Essays, was published. In the same year, he accepted a teaching position in nature philosophy at New College in Manchester. The school was “opposed to the Anglican Church,” and in 1800 it started to face financial difficulties and failed to pay wages. Dalton resigned from his position but stayed in Manchester. He made his living by giving private math and chemistry lessons. When he left New College, he was elected secretary of the Literary and Philosophical Society. He was assigned a chassis study room and a laboratory in the lodgings.

John Dalton lived a quiet life in this vibrant and rising British industrial city. He never married but had a certain number of close friends who deeply appreciated his gentle personality and simplistic and philosophical approach as a Quaker. Although he was not highly blessed in mathematics, his mind was extremely prone to numbers and mathematical concepts, which he applied to nature through intuition. However, he had a very lively scientific imagination. Keeping his conversations lean, away from controversy or falsehood, Dalton continued his research quietly, with intellectual courage and mental brilliance, which he never emphasized.

John Dalton: Heavy Elements

Due to his scientific interest, John Dalton turned to a more general examination of mixed gases and water-dissolved gases. He believed that the only way to fully understand these substances was to first deduce how heavy the absolute particles of the chemicals were. It was not possible to measure the atoms of various elements directly. Because they were too small to be measured and detected. However, he thought that there could be a way to find their relative weight. For this purpose, he assigned the weight of 1 to the lightest atom, namely hydrogen, and tried to determine the weight of each element’s atoms relative to 1. In Dalton’s ingenious method, the first step was to visualize how simple compounds such as water are formed if they could be observed at the invisible level of the particles. He knew that liquid water was composed of gaseous hydrogen and oxygen elements, but what would a single molecule of this substance look like?

He thought that the most likely answer would be to connect a single oxygen atom to a single hydrogen atom to form water. In today’s language, Dalton thought the water formula was HO at that time. The second step was to analyze the composition (or make use of the analysis of other chemists). Weight analysis of the water at that time indicated that it was composed of 7/8 oxygen and 1/8 hydrogen. Therefore, the oxygen atom must have been 7/8 of the weight of the water molecule.

In summary, if the hydrogen atom is the H1 weight unit and the water molecule is HO, and if it is seven-eighths oxygen, then it should be O=7. (We now know that this ratio is eight to nine.) He applied the same process to carbon, nitrogen, sulfur, and phosphorus compositions. These were the six atom weights from his first article that he read to the audience on the stage in October 1803. However, as the excerpt below shows, he mentioned nothing to the audience about how he arrived at these figures. We know this because of the notepad discovered in his lab (the notebook itself was destroyed by an airstrike in 1944, but the photostatic copy of the important pages was separately printed in 1896). The first atomic calculations in the document appear to have been entered on September 6, 1803. He maintained the computations in the months that followed.

The study of the relative weights of the particles is, to my knowledge, completely new; I have recently continued this review with remarkable success. In this article, the principle will not be mentioned; only the results will be presented, as far as they have been determined in my experiments.

From John Dalton’s 1803 oral presentation

The First True Atomic Theory

John Dalton’s method also had weaknesses; most notably, the only way to start the process was to guess how many atoms of each element were present in the molecules of these simple chemicals. This was certainly one reason why Dalton was concerned about revealing the details of his technique. These details were first published in 1807, in the chemistry book of Dalton’s friend Thomas Thomson, with proper reference to Dalton. Dalton later evaluated this theory in his new book, The New System of Chemical Philosophy, published in 1808–1810. He put forward the thesis that each element consists of a single, unique type of atom. The atoms in each element are different from those of other elements and thus have a different mass. They could not be altered or destroyed, but the atoms of different elements could combine in certain ways to form components of varying complexity. It was the first true scientific atomic theory derived from empirical experiments and analysis.

Some chemists refused to approve Dalton’s work, claiming that it was built on a hypothesis alone. Critics asked what reason Dalton had to assume that the water molecule was only HO and not HO2, H2O, or any other possibility.

Although John Dalton and his supporters acknowledged that a specific molecular formula recommendation should not be made blindly, they pointed out that the atomic weights determined by inference are derived from more than one formula and have a multi-faceted accuracy. Furthermore, the existence of some stable numerical regularity (compounds made up of the same elements always had a proportionate and integer number of atoms) ensured that chemicals are formed by the combining of atoms to create molecules.

The Molecular Formula of Water

Other chemists offered various versions of the atomic theory many years after Dalton’s ideas were published. Some, such as the British Humphry Davy and the Swedish Jöns Jacob Berzelius, believed that the water molecule was more likely made up of two hydrogen atoms since the two gases were united in an exact volume of one-to-two ratio to make water; water was H2O for them. However, for these scientists, this meant that the atomic weight of oxygen was 16 times that of hydrogen.

There were other conflicts; the history of atomic theory in the first half of the 19th century is very complex and controversial. However, despite these complexities, there is no doubt Dalton’s atomic theory has transformed science. Elements and compounds started to be represented with useful, clear acronyms. Chemical reactions were truly understandable at a level that was never possible before. Despite the ongoing weaknesses, the theory has become a powerful tool for other chemical discoveries.

Convinced of the correctness of his atomic weights, John Dalton kept his stance despite all objections to it. Even though no one else uses the weird notation system in which atoms are shown in different circles, he kept using it. 

40.000 People at John Dalton’s Funeral

Because of John Dalton’s modest personality, his value was not fully understood by his contemporaries. Everything aside, he came from a poor family. He lacked the educational and religious affiliation that leading European intellectuals deemed appropriate. With his behavior and speaking style, it was obvious that he was from the northern countryside. And the fact that he did not fully follow the rapid scientific developments in the 1820s and 1830s made the situation more difficult.

But Dalton’s real value has become increasingly apparent in the European scientific environment. In 1822, he traveled to Paris on his only trip abroad and was welcomed by a group of very famous scientists, including Laplace, Berthollet, Gay-Lussac, Cuvier, and Humboldt. He became a participating member of the French Academy of Sciences just by letter, and it was a great honor. Four years later, he received the first Royal Medal awarded by the Royal Society of London, of which he was a member. In 1833, the British government started to pay him 150 pounds per month for life. The amount doubled after four years.

John Dalton died in 1844. His body was placed in Manchester Town Hall and visited by 40.000 people who wanted to pay their respects for the last time; at the funeral the next day, the cortege was almost 2 km long.

John Dalton Quotes

• If I have succeeded better than many who surround me, it has been chiefly – may I say almost solely – from universal assiduity.
• Matter, though divisible in an extreme degree, is nevertheless not infinitely divisible. That is, there must be some point beyond which we cannot go in the division of matter. … I have chosen the word “atom” to signify these ultimate particles.
• No new creation or destruction of matter is within the reach of chemical agency. We might as well attempt to introduce a new planet into the solar system, or to annihilate one already in existence, as to create or destroy a particle of hydrogen.
• Reconsidering Happiness captures all the contradictory impulses of falling in and out of love-the lust and wanderlust, the contentment and restlessness, the secret loyalties, the hard compromises. Sherrie Flick has written a wise and elegant novel.