September 6, 1766, Cumberland (UK) – July 27, 1844, Manchester (UK)
He was born into a Quaker family and was sent to a school where he learned mathematics and excelled enough that, at the age of 12, he began teaching other children both at home and in the Quaker temple. His family income was modest so he devoted himself to agricultural work until in 1871 he became associated with one of his five brothers, Jonathan, who was helping one of his cousins to run a Quaker school in Kendal.
It is at this time that Dalton is influenced by a well-known Quaker meteorologist and instrument maker named Elihu Robinson who sparked his interest in mathematics and meteorology and led him to publish several books.
In 1790, Dalton was considering studying law or medicine, but his family did not support him, so he remained in Kendal until, in 1793, he moved to Manchester. Thanks to the teachings acquired by the philosopher and scholar John Gough, Dalton was appointed professor of mathematics and natural philosophy at the "New School" in Manchester, an academy of religious dissidents. He held the post until, in 1800, a financial crisis at the academy forced him to leave his post and begin a career as a private teacher.
Colour blindness
In 1794, Dalton was elected to the Manchester Literary and Philosophical Society, better known as "Lit&Phil", where he presented his first paper, "Extraordinary Facts Concerning Color Vision", which posited that deficiencies in color perception are due to abnormalities of the vitreous humor. It was the first time that not only the fact of the lack of color perception in some people was described, but also an explanation for the phenomenon was given. Although his theory was discredited while he was alive, his thorough and methodical investigation of his visual problem made such an impression that his name became the common term for color blindness, color blindness.
Dalton discovered that he saw colors differently while conducting botanical research and left instructions that his eyes be preserved, allowing DNA analysis, published in 1995, to show that he suffered from a less common type of color blindness. , deuteranopia. He was only able to see blue, purple, and yellow.
This blindness to certain colors sometimes hindered his scientific work, especially in the laboratory where he mixed up reagent bottles, or in social aspects, such as when he went to meet King William IV in 1832. He wore a scarlet academic dress, an unusual color for a man like him and that surprised his acquaintances. The reason was that Dalton saw her as dark gray.
Law of Partial Pressures
Between 1800 and 1802, when Dalton was secretary of Lit & Phil, he published four articles on the constitution of gas mixtures; the vapor pressure of water and other vapors at different temperatures, both in a vacuum and in air; about evaporation and the thermal expansion of gases. He concluded, from observations of the vapor pressure of six different liquids, that the change in vapor pressure for all liquids is equivalent, to the same change in temperature, determined from steam at any Pressure.
In 1810, Dalton postulated that: "The total pressure of a mixture of gases, which do not react chemically, is equal to the sum of the pressures that each gas would exert if it were alone in the container, without changing the temperature".
Atomic weights
En una entrada de su cuaderno de laboratorio fechada el 6 de septiembre de 1803, aparece una tabla de pesos relativos de átomos de seis elementos: hidrógeno, oxígeno, nitrógeno, carbono, azufre y fósforo, que derivan del análisis del agua, amoniaco, dióxido de carbono y otros compuestos de la época.
Afirmaba, por ejemplo, que los átomos del elemento de hidrógeno eran los más livianos que existían y que el peso de un átomo de hidrógeno era la dieciseisava parte del de un átomo de oxígeno, así que asignó al átomo de hidrógeno un peso de uno y al del oxígeno, dieciséis.
Ley de las proporciones múltiples o Ley de Dalton
"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 first has canonical and indistinct numbers as a ratio".
Dalton worked with the fact that some elements can be related to each other in different proportions to form different compounds. Thus, for example, there are two copper oxides, CuO and Cu2O, which have 79.89% and 88.82% copper, respectively, and are equivalent to 3.974 grams of copper per gram of oxygen in the first case and 7,945 grams of copper per gram of oxygen in the second. The ratio between both quantities is 1:2 as it is currently expressed with the formulas of the compounds derived from the atomic theory.
In 1808, in his work "A New System of Chemical Philosophy", compounds were listed as binary, ternary, quaternary, etc., based on the number of atoms the compound had in its simplest form, the empirical form.
In that publication, Dalton used his symbols to visually represent the atomic structure of compounds.
This law was demonstrated by the French chemist and physicist Louis Joseph Gay-Lussac.
Atomic theory
In 1803, he presented the first system of symbols and abbreviations for the names of the elements, becoming the first atomic graphic designer in history and expanding the list of 33 substances presented by Antoine Lavoisier to 36.
These symbols made it possible to convert the chemical language into a universal language. The drawback was that it did not have the approval of all chemists and did not establish clear rules to expand the catalog of symbols in the event of discovering new elements.
Currently, the system created by the Swedish chemist Jöns Jacob Berzelius in 1814 which is partially based on the one presented by Dalton is used. He simplified the system by organizing it into 47 letters that corresponded to the initials of the element's name in Latin, as was being done in other disciplines, and adding a second letter when there was a need to differentiate between two elements whose name began with the same letter. initial.
Berzelius's proposal was more widely accepted among chemists because it allowed the writing of chemical elements to be combined with ordinary text, avoiding much of the confusion generated by Dalton's symbols.
Between 1803 and 1808 he proposed what would be the first scientifically based model, although he called it "atomic theory" in which it was postulated that:
- Matter is made up of atoms, indivisible units of matter that can neither be generated nor destroyed.
- The atoms of a specific element have the same size, weight, and qualities and the atoms of different elements have different characteristics from each other.
- Compounds are formed by the combination of atoms of two or more different elements.
- Although they can be combined to form different compounds, the atoms themselves remain unchanged, and cannot be divided or destroyed.
- The same compound is always produced by the same proportion in the combination of atoms.
- The combination of different types of atoms is carried out through simple relationships.
- The combination of two specific elements can give rise to different compounds depending on the proportions in which they are mixed.
- In chemical reactions it is possible to create, dissociate, or transform molecules, these being a reorganization of the atoms that make up each compound.
Dalton's atomic theory has been one of the most important in science when it comes to describing the structure of matter. However, since it was published there have been great advances that have shown that some postulates are not true:
- "The atom is a basic and indivisible unit." Fake. It has been possible to distinguish within the atom different parts formed by subatomic structures such as protons, neutrons, and electrons.
- "All atoms of the same substance have the same properties." Fake. Atoms of different electrical charges can be found depending on the balance between protons and electrons (what is known as ions), as well as different atomic masses of the same element (isotopes).
- "Atoms are unmodifiable." Fake. It has been shown that this is not the case with the advent of nuclear fission and fusion.
Despite this, Dalton's theory has laid the foundations for modern chemistry and has allowed a great advance in the understanding of matter and its behavior.
