Historical development of atomic structureYazan FahmawiSept. 30, 1995T3 Chemistry IBSMme. RedmanThe idea behind "the atom" dates back to ancient Greek society, where scientists believed that all matter was made up of smaller, more fundamental particles called elements. They called these particles atoms, which means “not divisible.” Then came the chemists and physicists of the 16th and 17th centuries who discovered various formulas of various salts and water, thus discovering the idea of ​​a molecule. Then, in 1766, a man was born named John Dalton, who was born in England. He is known as the father of atomic theory because it was he who made it quantitative, that is, he discovered many masses of various elements and, in connection, discovered the different proportions in which molecules are formed (i.e. for each water molecule, one atom). of oxygen and two molecules of hydrogen are required). He also discovered noble or inert gases and their inability to react with other substances. In 1869, a Russian chemist, best known for developing the periodic law of properties of chemical elements (which states that elements exhibit a regular pattern ("periodicity") when arranged according to their atomic mass), published his first attempt to classify the known elements. His name was Mendeleev and he was a renowned teacher. As no good chemistry textbooks were available at the time, he wrote the two-volume Principles of Chemistry (1868–1870), which later became a classic. When writing this book, Mendeleev attempted to classify the elements according to their chemical properties. In 1871 he published an improved version of the periodic table, in which he left spaces for as yet unknown elements. His chart and theories were accepted by the scientific world when three elements he had “predicted” – gallium, germanium and scandium – were subsequently discovered. In 1856, another important figure in atomic theory was born: Sir Joseph John Thomson. In 1906, after teaching at the University of Cambridge and Trinity University in England, he won the Nobel Prize in physics for his work on the conduction of electricity through gases. He discovered what an electron is thanks to cathode rays. An electron is the smallest particle in an atom, whose mass is negligible compared to the rest of the atom and whose charge is negative. Although scientists didn't know it at the time, electrons were located in a cloud of electrons rotating around the nucleus, or center of the atom. Another prominent figure in nuclear physics is a man called Ernest Rutherford, born in 1871. He was also a professor at the University of Cambridge, the University of Manchester (both in England), and McGill College.