And if at that time Boyle's ideas were established that there are "simple bodies" (chemical elements) and "perfect mixtures" (chemical compounds) and any "perfect mixtures" can be divided into "simple bodies", then in the book "The New System of Chemical Philosophy" of 1808, John Dalton put forward the first idea about which of the substances, to which type is subject. But before that, Lavoisier proved that mass is constant, it does not disappear anywhere and does not appear out of nowhere. Davy also discovered a number of chemical elements: hydrogen, oxygen, nitrogen, carbon, sulfur, phosphorus, sodium and potassium were discovered by him in 1807, and in 1808 he also discovered such elements as calcium, strontium, barium and magnesium. Iron, zinc, copper, lead, silver, platinum, gold and mercury were also discovered.
Their discovery did not take much more work, since many of them were isolated from ores, isolated from chemical compounds. And already water, ammonia, carbon dioxide and many other compounds were already considered perfect mixtures. And now, Dalton, having everything he needed, decided to determine the atomic masses of all chemical elements, and also enter them all into tables, that is, classify them. So, Dalton introduced his own designation for each chemical element, for example, for hydrogen he introduced a circle icon with a dot in the center, for oxygen there was a sign – an ordinary circle, and for carbon there was a sign of a painted black circle, etc. To calculate the masses of atoms, Dalton conducted some experiments.
Initially, he evaporated water, and on the upper part he installed substances with which hydrogen reacted better, calculating changes in both the mass of the substance with which the interaction took place or from the volume of steam, Dalton could determine which part of the water consists of hydrogen and which of oxygen. Thus, having determined that 1/8 of the total mass of water consists of hydrogen, and 7/8 of oxygen, Dalton decided that oxygen is heavier than hydrogen and assigned a mass equal to 1 to hydrogen and 7 to oxygen. The same analysis of ammonia showed 1 for hydrogen and 5 for nitrogen. After analyzing it in this way, Dalton compiled his own table of chemical elements.
Needless to say, although this was the first step on the path of knowledge, all these statements were not true. But it lasted for quite a long time and various assumptions were based on it. One of these hypotheses was published in the journal "Philosophical Annals" by the London physician William Prout and was devoted to the idea that all atoms consist of hydrogen. But of course, this hypothesis was not true like many other assumptions of that time.
And if then, the atomic unit of mass was taken as the mass of a hydrogen atom, then today the exact unit is considered to be 1/12 of the mass of a carbon atom and is named as an A. E. M. or atomic unit of mass. And chemical elements today are usually designated from the first two or one letter of their name in Latin, for example, hydrogen is designated as H due to the name Hydrogenium («Generating water» in Latin), Nitrogen – N or Nitrogenium – «Giving birth to saltpeter», iron – Fe or Ferrum, copper – Cu – Cuprum, carbon – C – Carboneum. This system was adopted on September 3, 1860 after the Italian chemist Stanislao Cannizzaro at the International Congress in Karlsruhe proposed this method in his speech.
After that, it was customary to record chemical compounds using these symbols, and the number of atoms was indicated in the lower right corner, so for example, the compound of carbon and hydrogen (water) is written as H2O, ammonia – NH3, sulfuric acid H2SO4, etc. This method is very convenient because it creates opportunities for using symbolic notation and not there is no need to write down all the symbols several times, for example, for a cane sugar molecule – C6H12O6 (6 carbon atoms, 12 hydrogen atoms and 6 oxygen atoms). Instead of CCCCCCHHHHHHHHHHHOOOOOO, you can easily and simply write C6H12O6.
If everything is already clear with the notation, then there remains one very interesting consequence. Taking into account the fact that 1 atomic unit of mass is equal to 1/12 of a carbon atom, this makes it possible to calculate the masses of all chemical elements using compounds with carbon. For a better explanation, let’s give an example. Suppose there is a certain compound of carbon and hydrogen, if you act on it with an electric current or heat it, then it is possible, if it is solid, to melt, if the liquid is evaporated and to obtain a finite volume of carbon and hydrogen. From the ratio of their masses and volumes, it is possible to determine how many hydrogen atoms account for one carbon atom, and already from the ratio of their masses, it is possible to calculate the mass of hydrogen. So if we divide the methane compound into carbon and hydrogen, we get 4 times more hydrogen than carbon in volume, so we can conclude that for 1 carbon atom, there are 4 hydrogen atoms and the CH4 compound is obtained. And as for the masses, in this ratio it turns out that the mass of 1 hydrogen atom is almost 1/12 of the mass of a carbon atom or 1.00811 am. Exactly the same method can be used to determine the masses for all other atoms (Table 1.1).
But what exactly is this value equal to 1 A. E. M.? If you answer this question, you can find the masses of all other types of atoms, at the same time prove their reality. But none of the atoms, even the largest of them, can be seen in any microscope at that time. The situation is saved by the discovery made in 1828 by the English botanist Robert Brown. When a new microscope was brought to Robert Brown, he left it in the garden, and in the morning, dew drops formed on the "table" of the microscope, and Brown himself forgot to wipe them and automatically looked into the microscope. What was his surprise when he saw that the pollen particles in the dew drop were randomly moving. The particles are not alive and cannot move by themselves. It just couldn't be. But then, when this movement was recorded, some assumptions and hypotheses appeared to explain this phenomenon.
Perhaps this movement was explained by the fact that there are flows in the drop itself due to pressure and temperature differences, such as, for example, the movement of dust particles in the air. After all, if microscopic objects have such a movement, then it must also be in particles with a large size, like dust particles. After all, the movement of dust particles is explained precisely by air flows. But this idea was not confirmed, because the particles did not move in the same direction. After all, in the flow or flow of a jet of air, water or other medium, particles should move only in one direction, and the movement of microscopic particles in Brownian motion does not depend on each other.
In that case, perhaps this movement is the result of the environment? From external sounds, table shakes and other objects? This statement has already been refuted by the French physicist Gui. After conducting a series of experiments, he compared the chaotic Brownian motion with the movement in a remote basement in the village with the movement in the middle of a noisy street. The movements, of course, affected, but they affected only the entire drop as a whole, and not the Brownian motion of the particles itself. Moreover, there was the same movement in gases as in liquids, a striking example of such a movement is the movement of coal particles in tobacco smoke. For a visual example, you can compare two pictures.