be transcribed and rational conclusions can be obtained. After an experiment has been carried out, a chemist can state a theory which is a tested explanation of a natural occurrence. Based on scientific principles, Chemistry didn't evolve until the latter part of the 18th century. Chemists started to measure exactly what the substances were in their experiments. In 1805, John Dalton's atomic theory helped to advance modern chemistry. This theory stated that all matter is made up of small particles called atoms and that chemical changes take place between these atoms and groups of atoms. Soon after, Joseph Proust came out with the law of definite proportions and Joseph Gay-Lussac brought forth the law of definite proportions. Amedeo Avogadro also came out with the hypothesis, a planned explanation of a regularity in nature, that can be stated in modern terms: Equal volumes of all gases under the same conditions of temperature and pressure contain the same number of molecules. Jns Berzelis analyzed hundreds of compounds and published accurate tables of atomic weights in 1826. Friedrich Whler's synthesis of urea in 1828 started organic chemistry beginning the concept of organic compounds having geometric structure. In 1834, Michael Faraday started electrochemistry. Only about sixty elements were known by the middle of the nineteenth century. Dmitri Mendeleev published the first periodic table, which orders the chemically different kinds of atoms in a way that highlights similarities among the elements, in 1869. The table orders these elements in rows and columns, with all the elements arranged by atomic number. This table brought about the beginning of theoretical chemistry. Robert Bunsen also contributed to this period with the invention of the Bunsen burner and many other instruments used in modern chemistry. Optical activity of some isomers was discovered by Louis Pasteur, whose work innovated biochemistry. Physical chemistry became i...
