With an atom through the ages - part 1
Content
The last century is often referred to as the "age of the atom". At that not too distant time, the existence of the “bricks” that make up the world around us was finally proved, and the forces dormant in them were released. The idea of the atom itself, however, has a very long history, and the story of the history of knowledge of the structure of matter cannot be started otherwise than with words referring to antiquity.
1. A fragment of Raphael's fresco "The School of Athens", depicting Plato (on the right, the philosopher has the features of Leonardo da Vinci) and Aristotle
"Already old..."
… philosophers came to the conclusion that all nature consists of imperceptibly small particles. Of course, at that time (and for a long time after that) scientists did not have the opportunity to test their assumptions. They were only an attempt to explain the observations of nature and answer the question: "Can matter decay indefinitely, or is there an end to fission?«
Answers were given in various cultural circles (primarily in ancient India), but the development of science was influenced by the studies of Greek philosophers. In last year's holiday issues of "Young Technician", readers learned about the centuries-old history of the discovery of elements ("Dangers with the Elements", MT 7-9/2014), which also began in Ancient Greece. Back in the XNUMXth century BC, the main component from which matter (element, element) is built was searched for in various substances: water (Thales), air (Anaximenes), fire (Heraclitus) or earth (Xenophanes).
Empedocles reconciled them all, declaring that matter consists not of one, but of four elements. Aristotle (1st century BC) added another ideal substance - ether, which fills the entire universe, and declared the possibility of transformation of elements. On the other hand, the Earth, located at the center of the universe, was observed by the sky, which was always unchanged. Thanks to the authority of Aristotle, this theory of the structure of matter and the whole was considered correct for more than two thousand years. Became, among other things, the basis for the development of alchemy, and therefore of chemistry itself (XNUMX).
2. Bust of Democritus of Abdera (460-370 BC)
However, another hypothesis was also developed in parallel. Leucippus (XNUMXth century BC) believed that matter is composed of very small particles moving in a vacuum. The views of the philosopher were developed by his student - Democritus of Abdera (c. 460-370 BC) (2). He called the “blocks” that make up matter atoms (Greek atomos = indivisible). He argued that they are indivisible and unchanging, and that their number in the universe is constant. Atoms move in a vacuum.
When atoms they are connected (by a system of hooks and eyes) - all kinds of bodies are formed, and when they are separated from each other - the bodies are destroyed. Democritus believed that there are infinitely many types of atoms, differing in shape and size. The characteristics of atoms determine the properties of a substance, for example, sweet honey is made up of smooth atoms, and sour vinegar is made up of angular ones; white bodies form smooth atoms, and black bodies form atoms with a rough surface.
The way the material is joined also affects the properties of matter: in solids, atoms are tightly adjacent to each other, and in soft bodies they are located loosely. The quintessence of the views of Democritus is the statement: "In fact, there is only emptiness and atoms, everything else is an illusion."
In later centuries, the views of Democritus were developed by successive philosophers, some references are also found in the writings of Plato. Epicurus - one of the successors - even believed that atoms they consist of even smaller components (“elementary particles”). However, the atomistic theory of the structure of matter lost to the elements of Aristotle. The key—already then—was found in experience. Until there were tools to confirm the existence of atoms, the transformations of elements were easily observed.
For example: when water was heated (cold and wet element), air was obtained (hot and wet steam), and soil remained at the bottom of the vessel (cold and dry precipitation of substances dissolved in water). The missing properties - warmth and dryness - were provided by fire, which heated the vessel.
Invariance and constant number of atoms they also contradicted observations, as microbes were thought to emerge "out of nothing" until the XNUMXth century. The views of Democritus did not provide any basis for alchemical experiments related to the transformation of metals. It was also difficult to imagine and study the infinite variety of kinds of atoms. The elementary theory seemed much simpler and more convincingly explained the surrounding world.
3. Portrait of Robert Boyle (1627–1691) by J. Kerseboom.
Fall and rebirth
For centuries, atomic theory has stood apart from mainstream science. However, she did not finally die, her ideas survived, reaching European scientists in the form of Arabic philosophical translations of ancient writings. With the development of human knowledge, the foundations of Aristotle's theory began to crumble. The heliocentric system of Nicolaus Copernicus, the first observations of supernovae (Tycho de Brache) arising from nowhere, the discovery of the laws of motion of the planets (Johannes Kepler) and the moons of Jupiter (Galileo) meant that in the sixteenth and seventeenth centuries, people ceased to live under the sky unchanged from the beginning of the world . On earth, too, was the end of the views of Aristotle.
The centuries-old attempts of alchemists did not bring the expected results - they failed to turn ordinary metals into gold. More and more scientists questioned the existence of the elements themselves, and remembered the theory of Democritus.
4. The experiment of 1654 with the Magdeburg hemispheres proved the existence of vacuum and atmospheric pressure (16 horses cannot break neighboring hemispheres from which air was pumped out!)
Robert Boyle in 1661 gave a practical definition of a chemical element as a substance that cannot be broken down into its components by chemical analysis (3). He believed that matter consists of small, solid and indivisible particles that differ in shape and size. Combining, they form molecules of chemical compounds that make up matter.
Boyle called these tiny particles corpuscles, or "corpuscles" (a diminutive of the Latin word corpus = body). Boyle's views were undoubtedly influenced by the invention of the vacuum pump (Otto von Guericke, 1650) and the improvement of piston pumps for compressing air. The existence of a vacuum and the possibility of changing the distance (as a result of compression) between air particles testified in favor of the theory of Democritus (4).
The greatest scientist of the time, Sir Isaac Newton, was also an atomic scientist. (5). Based on the views of Boyle, he put forward a hypothesis about the fusion of the body into larger formations. Instead of the ancient system of eyelets and hooks, their tying was - how else - by gravity.
5. Portrait of Sir Isaac Newton (1642-1727), by G. Kneller.
Thus, Newton united the interactions in the entire Universe - one force controlled both the movement of the planets and the structure of the smallest components of matter. The scientist believed that light also consists of corpuscles.
Today we know that he was "half right" - numerous interactions between radiation and matter are explained by the flow of photons.
Chemistry comes into play
Until almost the end of the XNUMXth century, atoms were the prerogative of physicists. However, it was the chemical revolution initiated by Antoine Lavoisier that made the idea of the granular structure of matter generally accepted.
The discovery of the complex structure of the ancient elements - water and air - finally refuted Aristotle's theory. At the end of the XNUMXth century, the law of conservation of mass and the belief in the impossibility of the transformation of elements also did not cause objections. Scales have become standard equipment in the chemical laboratory.
6. John Dalton (1766-1844)
Thanks to its use, it was noticed that the elements combine with each other, forming certain chemical compounds in constant mass proportions (regardless of their origin - natural or artificially obtained - and the method of synthesis).
This observation has become easily explicable if we assume that matter consists of indivisible parts that make up a single whole. atoms. The creator of the modern theory of the atom, John Dalton (1766-1844) (6), followed this path. A scientist in 1808 stated that:
- Atoms are indestructible and immutable (this, of course, ruled out the possibility of alchemical transformations).
- All matter is made up of indivisible atoms.
- All atoms of a given element are the same, that is, they have the same shape, mass and properties. However, different elements are made up of different atoms.
- In chemical reactions, only the way of joining atoms changes, from which molecules of chemical compounds are built - in certain proportions (7).
Another discovery, also based on observing the course of chemical changes, was the hypothesis of the Italian physicist Amadeo Avogadro. The scientist came to the conclusion that equal volumes of gases under the same conditions (pressure and temperature) contain the same number of molecules. This discovery made it possible to establish the formulas of many chemical compounds and determine the masses atoms.
7. Atomic symbols used by Dalton (New System of Chemical Philosophy, 1808)
8. Platonic solids - symbols of atoms of ancient "elements" (Wikipedia, author: Maxim Pe)
How many times to cut?
The emergence of the idea of the atom was associated with the question: "Is there an end to the division of matter?". For example, let's take an apple with a diameter of 10 cm and a knife and start slicing the fruit. First, in half, then half an apple into two more parts (parallel to the previous cut), etc. After a few times, of course, we will finish, but nothing prevents us from continuing the experiment in the imagination of one atom? A thousand, a million, maybe more?
After eating a sliced apple (delicious!), Let's start the calculations (those who know the concept of a geometric progression will have less trouble). The first division will give us a half of the fruit with a thickness of 5 cm, the next cut will give us a slice with a thickness of 2,5 cm, etc. ... 10 beaten ones! Therefore, the "path" to the world of atoms is not long.
*) Use a knife with an infinitely thin blade. In fact, such an object does not exist, but since Albert Einstein in his research considered trains moving at the speed of light, we are also allowed - for the purposes of a thought experiment - to make the above assumption.
Platonic atoms
Plato, one of the greatest minds of antiquity, described the atoms of which the elements were to be composed in the Timachos dialogue. These formations had the form of regular polyhedra (Platonic solids). So, the tetrahedron was an atom of fire (as the smallest and most volatile), the octahedron was an atom of air, and the icosahedron was an atom of water (all solids have walls of equilateral triangles). A cube of squares is an atom of the earth, and a dodecahedron of pentagons is an atom of an ideal element - the celestial ether (8).
