The same chemical compound has a permanent staff, regardless of the location and method of sample preparation.This is the conclusion one of the first to come to the founder of modern chemistry, French scientist Antoine de Lavoisier.He was able to determine the composition of water, air and organic matter, believed that the particles are part of the substances in certain proportions.Later, another chemist from France JL Proust was formulated law of definite proportions.Both researchers have put a lot of effort to defend their ideas in a dispute with the scientific community.
views on the structure of matter at the turn of the XVIII and XIX centuries
Chemical elements, connected to each other in different proportions, form a set of substances.Each of these is characterized by a certain set of atoms and the ratio of their masses.But before the end of the XVIII century, many scientists believed otherwise.The problem for them was malfunctioning quantitative methods.In addition, the position of atomic and molecular beliefs at the time were tenuous sway phlogiston theory - the mythical element.The establishment of the quantitative composition of matter made a significant contribution:
- A. de Lavoisier;
- JL Proust;
- D. Dalton.
merit JL Proust is that he improved quantitative methods Lavoisier strictly follow them.The scientist proposed law of definite proportions, saving ratios of elements in samples of compounds.Work in this direction Proust began at the end of the XVIII century, but his works have received recognition only in 1808.John Dalton around the same time introduced the concept of atoms and masses of these particles, multiple ratios.
Biography JL Proust
scientist who proposed the law of constant composition, was born on September 26, 1754 in the west of France.Father Joseph Louis was a pharmacist in the city of Angers.He and his son accustomed to experiments with chemical substances.The young man continued his studies in Paris, where he met with Lavoisier and his scientific ideas.In 1776, Proust published his first major works in the field of chemistry.From 1799 to 1806 he headed the laboratory scientist in Madrid.Proust returned to France in 1806.After a brief stay in Paris, Louis Joseph went to their homes.In the years 1808-1816 were recognized his work in the study of the composition of substances, including glucose.In 1817 he retired and lived alone until his death (1826).Proust was one of the outstanding scientists of his time, a Knight of the Legion of Honor, a member of the Royal Academy of Sciences, Naples,.
law of definite proportions.Examples
JL Proust opened glucose, famous for his brilliant victory in the scientific polemics with compatriot Berthollet, the cause of which was the law of definite proportions.The wording suggested Proust, says that when some elements form a chemically pure sample, it consists of the same atoms.The relationship of the masses and their numbers also are permanent.Examples:
- Sodium chloride (NaCl) can be prepared by reacting hydrochloric acid with sodium hydroxide.The second method - Treatment with hydrochloric acid, sodium carbonate.In two separate chemical reactions to obtain compounds whose formula is NaCl.And in the first and in the second case, the substance contains 39.33% and 60.66% sodium chloride.
- oxygen (chemical symbol O) in the formation of a water molecule binds to the same amount of hydrogen (H).If hydrogen is reacted with 1.11 g of 8.89 g of oxygen, is formed 10 g of water (H2O).Increasing amounts of one of the substances leads to the same result.Do not react atoms of the element, which took in excess.The mass of water in this experiment is the same - 10 g, composition reflects its molecular formula is H2O.
opening value constant composition
At the beginning of the XIX century in theoretical chemistry approved a law that connect agents describe their relationship.We studied the qualitative and quantitative characteristics of many scientists who proposed generic formulation.The fundamental idea was Lomonosov on the conservation of mass in chemical reactions.Established JL Proust law of definite proportions and of great importance to science and practice.On the basis of this relationship formula water is recorded only in the form of H2O, and the composition of the sulfuric acid - H2SO4.But the law of Proust has no such comprehensive nature as a teaching University.Therefore, its wording clarified after the discovery of isotopes.So we call the atoms of the same element with different masses.The ratio of particles in the sample is constant, but only if the constant isotopic composition.For example, the mass composition of hydrogen and oxygen in a conventional and heavy water differs.The second liquid contains an isotope of hydrogen - deuterium.The mass of heavy water more than usual.
Modern views on the substance
In accordance with the wording of Proust, the weight ratio of the atoms that make up a particular substance is permanent, does not depend on the method of sample preparation.At the beginning of the XX century in the study of metal alloys were discovered compounds with varying composition.In this case, the unit weight of one chemical element may correspond to different masses of another element.For example, in the compounds of thallium and bismuth per unit mass of the first falls from 1.2 to 1.8 weight units of the second element.Such examples can be found among the intermetallic compounds, oxides of sulfur, nitrogen, carbon, hydrogen and metals.Consequently, the laws discovered by Proust and Dalton, fully valid only for substances that have a molecular structure.These include many acids, oxides, hydrides.Qualitative and quantitative structure of these compounds is constant.For example, the composition of the water in the atmosphere, the oceans, glaciers and living organisms reflects the formula H2O.