Tag Archives: Atomic Theory

Arts, History, Philosophy, Science

Quantum Leaps: John Dalton

1766–1844

FOR much of his life, the primary interest of John Dalton, an English Quaker, was the weather. Living in the notoriously wet country of Cumbria, he maintained a daily diary of meteorological occurrences from 1787 until his death, recording in total some 200,000 entries. It was, however, his development of atomic theory for which he is most remembered.

Different atoms – It was around the turn of the nineteenth century that Dalton started to formulate his theory. He had been undertaking experiments with gases, in particular on how soluble they were in water. A teacher by profession, who only practised science in his spare time, he had expected different gases would dissolve in water in the same way, but this was not the case. In trying to explain why, he speculated that perhaps the gases were composed of distinctly different “atoms”, or individual particles, which each had different masses. Of course, the idea of an atomic explanation of matter was not new, going way back to Democritus of Abdera (c. 460–370 BCE) in ancient Greece, but now Dalton had the discoveries of recent science to reinforce his theory. On further examination of his thesis, he realised that not only would it explain the different solubility of gases in water, but would also account for the “conservation of mass” observed during chemical reactions as well as the combinations into which elements apparently entered when forming compounds (because the atoms were simply “rearranging” themselves and not being created or destroyed).

Atomic theory – Dalton publicly outlined his support for this atomic theory in a lecture in 1803, although its complete explanation had to wait until his book of 1808 entitled A New System of Chemical Philosophy. Here, he summarised his beliefs based on key principles, including: atoms of the same element are identical; distinct elements have distinct atoms; atoms are neither created nor destroyed; everything is made up of atoms; a chemical change is simply the reshuffling of atoms; and compounds are made up of atoms from the relevant elements. In the same book he published a table of known atoms and their weights, although some of these were slightly wrong due to the crudeness of Dalton’s equipment, based on hydrogen having a mass of one. It was a basic framework for subsequent atomic tables, which are today based on carbon (having a mass of 12), rather than hydrogen. Dalton also erroneously assumed elements would combine in one-to-one ratios (for example, water being HO not H2O) as a base principle, only converting into “multiple proportions” (for example, from carbon monoxide, CO, to carbon dioxide, CO2) under certain conditions. Although scientific arguments over the validity of Dalton’s thesis would continue for decades, the foundations for the study of modern atomic theory had been laid and with ongoing refinement were gradually accepted.

Prior to atomic theory, Dalton had also made a number of other important discoveries and observations in the course of his work. These included his “law of partial pressures” of 1801, which stated that a blend of gases exerts pressure which is equivalent to the total of all the pressures each gas would wield if they were alone in the same volume as the entire mixture.

Dalton also explained that air was a blend of independent gases, not a compound. He was the first to publish the law later credited to and named after Jacques-Alexandre-César Charles (1746–1823). Although the Frenchman had been the first to articulate the law concerning the equal expansion of all gases when raised in equal increments of temperature, Dalton had discovered it independently and had been the first to publish.

Dalton also discovered the “dew point” and that the behaviour of water vapour is consistent with that of other gases, and hypothesised on the causes of the aurora borealis, the mysterious Northern Lights. His further meteorological observations included confirmation of the cause of rain being due to a fall in temperature not pressure.

Further achievements – John Dalton began teaching at his local school at the age of 12. Two years later, he and his elder brother purchased a school where they taught some 60 children.

His paper on colour blindness, which both he and his brother suffered from, and which was known as daltonism for a long while, was the first to be published on the condition. Dalton is also largely responsible for transferring meteorology from being an imprecise art on folklore to a real science.

Chronology  

. 1793 Meteorological Observations and Essays published

. 1801 Dalton states his Law of Partial Pressure

. 1803 Outlines his atomic theory in a lecture. This transformed the basics of chemistry and physics

. 1808 A New System of Chemical Philosophy published.

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Philosophy, Science

Philosophy and science

THE PERTINENCE OF PHILOSOPHY vs. SCIENCE

THROUGHOUT much of the history of philosophy, there was no such thing as science in its modern form: in fact, it was from philosophical enquiry that modern science has evolved. The questions that metaphysics set out to answer about the structure and substance of the universe prompted theories that later became the foundations of “natural philosophy”, the precursor of what we now call physics. The process of rational argument, meanwhile, underpins the “scientific method”.

Since the 18th century, many of the original questions of metaphysics have been answered by observation, experiment and measurement, and philosophy appeared to be redundant in these areas. Philosophers have since changed their focus to examine science itself. Some, like Hume, challenged the validity of inductive reasoning in science, while others sought to clarify the meaning of terms used by science, opening up a “philosophy of science” that considers areas such as scientific ethics and the way science makes progress.

ADVANCES IN SCIENCE

MOST of the sciences evolved from branches of philosophy, complementing them with scientific theories describing the physical world. But as the pace of progress accelerated with the scientific revolution of the Enlightenment, the natural sciences largely replaced metaphysics, and by the end of the 19th century psychology and neuroscience began to provide a scientific alternative to the philosophy of the mind.

In the 20th century, Albert Einstein’s theories seemed to provide a comprehensive explanation of the physical universe, but many aspects of the new physics threw up almost as many questions as answers – problems that science alone could not explain. And just as science appeared to be replacing aspects of philosophy, some philosophers turned their attention to science itself. Karl Popper proposed a practical answer to the problem of induction, the basis of scientific methods, while Paul Feyerabend questioned the notion of a single reliable scientific method, based on Thomas Kuhn’s idea that science makes advances not in a smooth progression, but in radical jumps.

. On the Origin of Species

The cultural influence of science reached a climax in the mid-19th century with the publication in 1859 of Darwin’s On the Origin of Species. Although it was a scientific rather than a philosophical work, his theory of evolution by natural selection put many aspects of philosophy in a new perspective. In the same way as Copernicus’s proposal of a heliocentric universe challenged religious authority and became symbolic of emergent Renaissance humanism, Darwin’s explanation of evolution presented humans as just another animal – part of the natural world rather than separate from it. In his later Descent of Man, he applied the principles of evolutionary theory specifically to humans, explicitly stating for the first time that we have evolved from animals, and so challenging previous notions of man as superior to other animals because of his ability to reason. But perhaps most important in terms of its effect on philosophy was the implicit idea that humans are not the pinnacle of God’s creation, but merely a stage in the evolution of the natural world.

ATOMIC THEORY

In the 5th century BCE, the philosopher Leucippus and his pupil Democritus proposed the revolutionary notion that everything is composed of indestructible particles in empty space. In other words, it was through philosophy that Atomic Theory first emerged.

Like many other philosophers, the Atomists, as they were later known, attempted to explain the reality of motion and change. Parmenides had said that these are mere illusions, since motion requires the existence of a void, which he deemed a logical impossibility.

Atomists turned this argument on its head, however, suggesting that since motion is patently possible, the void must exist, and matter must be free to move within it. Since the movement of matter takes place at a microscopic level, it is not visible. Matter is formed of minute particles that Leucippus called “atoms”, which exist in empty space, and the changes that can be observed in the cosmos are due to the motion of these atoms in the void. Each atom is an eternal and unchanging entity, both indestructible and indivisible, but capable of joining with others to form different substances and objects.

Where Parmenides posited eternal, immutable unity, the Atomists proposed an infinite diversity of eternal particles that gives rise to an ever-changing cosmos.

Building blocks

According to the Atomists, the atom is the basic unit of every material substance. These building blocks of matter are constantly in motion in the void, and react with each other, being either mutually repelled or attracted. There are countless kinds of atoms, which join together in different combinations to form the huge variety of substances. They then separate as those substances decay. The atoms themselves are immortal, and remain intact. They continue their movement throughout the void, continually and ceaselessly combining, separating, and reforming.

NEED TO KNOW

> The void described by the Atomists is more than empty space – it is an absolute absence of matter, akin to a vacuum.

> The word “atom” comes from the Greek atomon, meaning “uncuttable” or “indivisible”.

Kinds of Atom

Democritus suggested that atoms come in a range of sizes and shapes, their properties determining the characteristics of different substances. He proposed that the atoms of liquids are smooth and can move freely past one another, while solids have more rigid atoms that move less and can connect with other atoms.

AIR – Air atoms are light and wispy, and move freely and independently

WATER – The smooth, round atoms of water give it its flowing, liquid character

IRON – Atoms of iron have hooks that interlock to give the metal its solidity

SALT – The taste of salt is caused by its jagged atoms acting on the tongue

“Nothing exists except atoms and empty space; everything else is opinion.” – Democritus (5th century BCE)

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