Classical chemistry

Classical chemistry

In Europe, the study of chemistry was conducted by alchemists with the goals of transforming common metals into gold or silver and inventing a chemical elixir that would prolong life. Although these goals were never achieved, there were some important discoveries made in the attempt.

Robert Boyle(1627-1691) studied the behavior of gases and discovered the inverse relationship between volume and pressure of a gas. He also stated that “all reality and change can be described in terms of elementary particles and their motion,” an early understanding of atomic theory.
In 1661, he wrote the first chemistry textbook, “The Sceptical Cymist,” which moved the study of substances away from mystical associations with alchemy and toward scientific investigation. the first steps in a new science: chemistry.
By the eighteenth century the alchemists who had once tried in vain to find the philosopher's stone and the elixir of life were only a memory; the search for knowledge was now conducted along genuinely scientific lines. Many new elements (such as nickel, platinum, manganese, nitrogen, and chlorine) and a few compounds (such as carbon dioxide and hydrochloric acid) had been identified. In England science was so far advanced that plans had been made for the industrial production of sulfuric acid.
The mysterious substance: phlogiston
Despite this increasing knowledge, scientists were still hampered in their researches by an unfortunate theory which today seems to be a last relic of the age of the alchemists. It was thought that all combustible materials contained a mysterious substance called phlogiston, the principle of fire. When materials burned, it was the phlogiston that was seen to escape in the form of flames. Even when it was shown that the products of combustion weighed more than the original material, this was accounted for by the belief that the phlogiston that had escaped must have a negative weight – that is, it weighed less than nothing.
The first strong evidence against phlogiston theory came from pneumatic chemists in Britain during the later half of the 18th century. Joseph Black, Joseph Priestley and Henry Cavendish all identified different gases that composed air; however, it was not until Antoine Lavoisier discovered in the fall of 1772 that, when burned, sulphur and phosphorus “gain[ed] in weight” that the phlogiston theory began to unravel.

In a series of experiments on the combustion of mercury, Lavoisier showed that in fact when mercury "burned" it combined with a part of the air – oxygen – and increased in weight. By the use of the balance he showed that the weight of the oxide formed was equal to the weight of the mercury and the oxygen that had combined with it. His experiments finally disproved the phlogiston theory, and the way now lay open to the proper understanding of other chemical reactions.
In later experiments Lavoisier discovered the nature of air and water. He has justly been called the father of modern chemistry.
By the 1700s, the Age of Enlightenment had taken root all over Europe. Joseph Priestley (1733-1804) disproved the idea that air was an indivisible element. He showed that it was, instead, a combination of gases when he isolated oxygen and went on to discover seven other discreet gases. Jacques Charles continued Boyles’ work and is known for stating the direct relationship between temperature and pressure of gases. In 1794, Joseph Proust studied pure chemical compounds and stated the Law of Definite Proportions — a chemical compound will always have its own characteristic ratio of elemental components. Water, for instance, always has a two-to-one ratio of hydrogen to oxygen.
Antoine Lavoisier (1743-1794) was a French chemist who made important contributions to the science. While working as a tax collector, Lavoisier helped to develop the metric system in order to ensure uniform weights and measures. He was admitted to the French Academy of Sciences in 1768. Two years later, at age 28, he married the 13-year-old daughter of a colleague. Marie-Anne Lavoisier is known to have assisted her husband in his scientific studies by translating English papers and doing numerous drawings to illustrate his experiments.
Lavoisier’s insistence on meticulous measurement led to his discovery of the Law of Conservation of Mass. In 1787, Lavoisier published "Methods of Chemical Nomenclature," which included the rules for naming chemical compounds that are still in use today. His "Elementary Treatise of Chemistry" (1789) was the first modern chemistry textbook. It clearly defined a chemical element as a substance that cannot be reduced in weight by a chemical reaction and listed oxygen, iron, carbon, sulfur and nearly 30 other elements then known to exist. The book did have a few errors though; it listed light and heat as elements.
Amedeo Avogadro (1776-1856) was an Italian lawyer who began to study science and mathematics in 1800. Expanding on the work of Boyle and Charles, he clarified the difference between atoms and molecules. He went on to state that equal volumes of gas at the same temperature and pressure have the same number of molecules. The number of molecules in a 1-gram molecular weight (1 mole) sample of a pure substance is called Avogadro’s Constant in his honor. It has been experimentally determined to be 6.023 x 1023 molecules and is an important conversion factor used to determine the mass of reactants and products in chemical reactions.
In 1803, an English meteorologist began to speculate on the phenomenon of water vapor. John Dalton (1766-1844) was aware that water vapor is part of the atmosphere, but experiments showed that water vapor would not form in certain other gases. He speculated that this had something to do with the number of particles present in those gases. Perhaps there was no room in those gases for particles of water vapor to penetrate. There were either more particles in the “heavier” gases or those particles were larger. Using his own data and the Law of Definite Proportions, he determined the relative masses of particles for six of the known elements: hydrogen (the lightest and assigned a mass of 1), oxygen, nitrogen, carbon, sulfur and phosphorous. Dalton explained his findings by stating the principles of the first atomic theory of matter.
⦁ Elements are composed of extremely small particles called atoms.
⦁ Atoms of the same element are identical in size, mass and other properties. Atoms of different elements have different properties.
⦁ Atoms cannot be created, subdivided or destroyed.
⦁ Atoms of different elements combine in simple whole number ratios to form chemical compounds.
⦁ In chemical reactions atoms are combined, separated or rearranged to form new compounds.

On 6 March 1869, Mendeleev  made a formal presentation to the Russian Chemical Society, titled The Dependence between the Properties of the Atomic Weights of the Elements, which described elements according to both atomic weight (now called relative atomic mass) and valence.This presentation stated that:
⦁ The elements, if arranged according to their atomic weight, exhibit an apparent periodicity of properties.
⦁ Elements which are similar regarding their chemical properties either have similar atomic weights (e.g., Pt, Ir, Os) or have their atomic weights increasing regularly (e.g., K, Rb, Cs).
⦁ The arrangement of the elements in groups of elements in the order of their atomic weights corresponds to their so-called valencies, as well as, to some extent, to their distinctive chemical properties; as is apparent among other series in that of Li, Be, B, C, N, O, and F.
⦁ The elements which are the most widely diffused have small atomic weights.
⦁ The magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body.
⦁ We must expect the discovery of many yet unknown elements – for example, two elements, analogous to aluminum and ⦁ silicon, whose atomic weights would be between 65 and 75.
⦁ The atomic weight of an element may sometimes be amended by a knowledge of those of its contiguous elements. Thus the atomic weight of ⦁ tellurium must lie between 123 and 126, and cannot be 128. (Tellurium's atomic weight is 127.6, and Mendeleev was incorrect in his assumption that atomic weight must increase with position within a period.)
⦁ Certain characteristic properties of elements can be foretold from their atomic weights.

Mendeleev published his periodic table of all known elements and predicted several new elements to complete the table in a Russian-language journal. Only a few months after, Meyer published a virtually identical table in a German-language journal. Mendeleev has the distinction of accurately predicting the qualities of what he called ekasilicon, ekaaluminium and ekaboron (germanium, galliumand scandium, respectively).