In many ways, the history of civilization is the history of chemistry — the study of matter and its properties. Humans have always sought to identify, use and change the materials in our environment. Early potters found beautiful glazes to decorate and preserve their wares. Herdsmen, brewers and vintners used fermentation techniques to make cheese, beer and wine. Housewives leached the lye from wood ash to make soap. Smiths learned to combine copper and tin to make bronze. Crafters learned to make glass; leatherworkers tanned hides. The difference between a physical reaction and a chemical reaction is composition. In a chemical reaction, there is a change in the composition of the substances in question; in a physical change there is a difference in the appearance, smell, or simple display of a sample of matter without a change in composition. Although we call them physical "reactions," no reaction is actually occurring. In order for a reaction to take place, there must be a change in the elemental composition of the substance in question. Thus, we shall simply refer to physical "reactions" as physical changes from now on.
In the late 8th century, Jābir ibn Hayyān , known in Europe as “Geber”, introduced a new approach to alchemy based on scientific methodology and controlled experimentation in the laboratory. Jabir is therefore considered by many the father of chemistry, others reserve the title for Robert Boyle. His book “The Skeptical Chymist” started the evolvement of alchemy into modern chemistry. Tobern Olof Bergman was the first to use diagrams and symbols to explain chemical reactions instead of prose Credited as the founder of Quantitative Analysis Considered one of the founders of analytical chemistry Discovers manganèse and tungsten (collaboration with C. W. Scheele) Most important paper (1775) “A Dissertation on Electric Attractions” , a listing of elements in order of affinity, used in chemical literature as late as 1808 First to use the term Organic Chemistry for chemistry of the living world. 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. 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.