Student Education Repository (மாணவர்கள் கல்விக் களஞ்சியம்): Today (July 27, 1844) is the Memorial Day of John Dalton, who first published a list of modern atomic theories and atomic weights.

Tuesday, July 26, 2022

Today (July 27, 1844) is the Memorial Day of John Dalton, who first published a list of modern atomic theories and atomic weights.

Today (July 27, 1844) is the Memorial Day of John Dalton, who first published a list of modern atomic theories and atomic weights.

John Dalton was born on September 6, 1766, in Eaglesfield, near Cockermouth, Cumberland, England, to a Quaker family. His father was a weaver. He received his early education from his father, Quaker John Fletcher, who ran a private school in the nearby village of Partsha Hall. Dalton's family was too bad to support him for long. And from the age of ten, he began to earn his living in the service of the wealthy local Quaker Elihu Robinson. In 1800, at the age of 34, he became secretary of the Manchester Literary Philosophical Society. The following year, he published his major research papers on the components of gases, such as vacuum and atmosphere, the pressure of steam and other gases at different temperatures, and so on.

Dalton studied the pressure of vapor at several points in the range of 0–100 (C (32 - 212 F) and proposed the theory that the vapor pressure of all liquids would be equal at equal temperature changes, observing the vapor pressure of many different liquids. Foremost among Dalton's discoveries was the atomic theory in chemistry. The doctrine, however, is deeply ingrained in his name, but the connection is not fully understood. The main features of Dalton's atomic theory are: All elements are made up of tiny particles called atoms. The atoms of a particular element all have the axis's exact size, mass, and properties. Atoms of different elements may be different from these.

The atom cannot be created, destroyed, or perforated. Atoms of different elements mix in whole proportions to form a chemical compound. In chemical reactions, atoms combine, separate, or modify. Dalton published the first list of atomic weights. It contained six elements: hydrogen, oxygen, nitrogen, carbon, sulfur, and phosphorus. It was constructed from the assumption of weight 1 for a hydrogen atom. Not much is known about how he first discovered this. But in his laboratory notebook, on September 6, 1803, there is a list of several atomic weights from a study of water, ammonia, and carbon dioxide.

In his first extended discussion of atomic theory (1808), Dalton proposed an additional (controversial) rule of "great simplicity". This rule could not be independently confirmed. But some such assumptions were necessary to propose formulas for some simple molecules. Based on the calculation of the atomic weights on which this rule is based, the atoms of two different elements form only one mixture, such as water, which produces hydrogen and oxygen, or ammonia, which has hydrogen and nitrogen. The molecules of that compound are considered to contain one atom of each element. For components known at the time, such as two oxides of carbon or three oxides of nitrogen, their combinations were considered as simple as possible. For example, if two such combinations are known, one must contain an atom of each element, and the other must contain one atom of one element and two atoms of the other.

This is an assumption derived from a belief in the simplicity of nature. Scientists have no evidence to determine how many atoms of each element combine to form molecules. But this or some other rule is absolutely necessary for any initial theory. This is because one needed a molecular formula to calculate atomic weights. He considered Dalton's "greatest simplicity rule", the formula for water OH and ammonia NH, completely different from our modern understanding (H2O, NH3). On the other hand, his rule of simplicity led him to propose modern formulas suitable for two oxides of carbon (CO and CO2). Despite the uncertainty at the center of Dalton's nuclear theory, the principles of the theory survived.

Shortly after arriving in Manchester in 1794, Dalton was elected a member of the "Lit & Phil" Literary and Philosophical Society of Manchester. A few weeks later, he wrote his first article, "Unusual Facts About Color Vision," where he noted a lack of color perception due to the discoloration of the liquid medium of eye vision. Since he and his brother were color blind, he realized that this condition must be hereditary. John Dalton, best known for advancing modern nuclear theory, the study of color blindness, and gases and liquids, passed away on July 27, 1844, in Manchester, Lancashire, England, at 77.

Source By: Wikipedia

Information: Ramesh, Assistant Professor of Physics, Nehru Memorial College, Puthanampatti, Trichy.