The Early History of Chemistry

The Greeks were one of the first civilizations to use chemistry. They pondered on the question of whether the world was made up of small indivisible particles (atoms) or infinitely small particles. Pseudoscience dominated the next several thousand years known as alchemy. Modern Chemistry (starting during the 16th century) was generally metallurgy (extraction of metals from ores)The first chemist to perform quantitative experiments was Robert Boyle, who measured the relationship between the pressure and volume of air. Boyle’s definition of an element was a substance which could not be broken down into simpler elements. The Greek system of four elements died. The phenomenon of combustion intrigued many seventeenth and eighteenth century scientists. Georg Stahl suggested that a substance called phlogiston flowed out of burning material. Oxygen gas was later discovered by Joseph Priestley an English clergyman and scientist who found to support vigorous combustion and was thus supposed to be low in phlogiston.

Fundamental Chemical Laws

By the late eighteenth century combustion had been studied greatly, and the gasses of carbon dioxide, nitrogen, hydrogen, and oxygen had been discovered. Antoine Lavoisier, a French chemist, who explained the true nature of combustion. His experiments were down meticulously, and verified the law of conservation of mass which stated that mass is neither created nor destroyed. Lavoisier finally named the element oxygen, not phlogiston. Then during the French Revolution, Lavoisier was associated with collecting taxes and was executed in 1794. Joseph Proust was another French chemist who showed that a given compound always contains exactly the same proportion of elements by mass, or known as the law of definite proportion. John Dalton believed that atoms created various compounds, and became well known for discovering the law of multiple proportions, which states when two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers.

Dalton’s Atomic Theory

Dalton’s theory goes that (1) each element is made up of tiny particles called atoms.(2) The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways. (3) Chemical compounds are formed when atoms of different elements combine with each other. A given compound always has the same relative numbers and types of atoms. (4) Chemical reactions involve reorganization of the atoms—changes in the way they are bound together. The atoms themselves are not changed in a chemical reaction.

Dalton prepared the first table of atomic masses, which many of the masses were proved wrong. The French chemist Gay-Lussac performed experiments in which he measured under constant temperature and pressure the volumes of gasses and the way they reacted with each other. Also the Italian chemist Amadeo Avogadro interpreted the results of Gay-Lussac’s experiments and proposed that at the same temperature and pressure, equal volumes of different gases contain the same number of particles (known as Avogadro’s Hypothesis). The Swedish chemist named Jons Jakob Berzelius discovered the elements cerium, selenium, silicon, and thorium and developed the modern symbols for the elements used in writing the formulas and compounds.

Early Experiments to Characterize the Atom

J. J. Thomson studied electrical discharges in partially evacuated tubes called cathode-ray tubes. Thomson found the rays of negatively charged particles were electrons. Thomson also determined the charge-to-mass ratio of an electron: e/m= -1.76 x 10^8 C/g. The C is coulombs and the m represents the electron mass in grams. He also stated that electrons are present in all atoms, and there must be some positive particle in atoms.