by Mario Falzon Chemistry defined as the science of the nature of matter and its transformations has been studied since classical antiquity, that is for more than 3000 years. Why has Chemistry always held a prominent place in the mind of most scientists? Since ancient civilizations, scientists used the study of Chemistry to: (i) extract metals from ores (ii) make pottery and glazes (iii) ferment beer and wine (iv) make pigments for cosmetics and paints (v) extract chemicals from plants for medicine and perfume (vi) make cheese (vii) dye cloth and tan leather (viii)change animal fat into soap (ix) make glass (x) make alloys like bronze and brass 1700 BC - 300 BC: The names of some common metals were already known during the reign of King Hammurabi of Babylon in 1700 BC. By 430 BC, Democritus, a philosopher of ancient Greece proclaimed a simple atomic theory, stating that all matter is composed of atoms and the atom is the simplest unit of matter. In 300 BC, Aristotle declared mistakenly that only four elements exist, namely fire, air, water and earth. All matter was made up of one or more of these four elements and matter had four properties: hot, cold, dry and wet. 300 BC - 300 AD: This period of history was characterized by the advent of alchemists who attempted to transmute existing cheap metals into gold. The substance used for this conversion was called Philosopher’s stone. In spite of many efforts by famous alchemists of the day, transmutation of cheap metals into gold never happened. 300 AD - 1200 AD: A dead era for the study of Chemistry. All ideas were again turned back to Aristotle whose studies continued to influence the slow development of Chemistry. 1200 AD - 1520 AD: The alchemists turned their efforts to medicine. They made several attempts to find a chemical concoction that would enable people to live longer and cure the world’s prevailing ailments. Calling this new medicine the elixir of life, they never succeeded either. 1520 AD - 1700 AD: Aristotle’s influence and the newly published scientific treatise by Robert Boyle The Skeptical Chemist signified the death of the theories proposed by the alchemists. This early form of Chemistry disappeared for ever. 1700 AD - 1774 AD: Johann Beecher’s idea of the existence of phlogiston was almost universally accepted among scientists. When a substance burns, phlogiston was supposedly added from the air to the flame of the burning object. In some cases, a new product was produced. For example, according to Beecher, when mercury oxide was heated strongly in air, it combined with phlogiston to produce mercury. 1774 AD - 1794AD: Joseph Priestly discovered oxygen, though he called this gas dephlogisticated air. He heated strongly mercury oxide, collected the colourless gas that evolved and burned different substances in it. At the same time, Antoine Lavoisier disproved the Phlogiston Theory and renamed the dephlogisticated air oxygen. He finally realized correctly that oxygen is that part of the air that combines with substances as they burn. Lavoisier’s discovery of oxygen earned him the title of the “Father of Modern Chemistry”. Lavoisier’s work also included the development of the law of conservation of mass by which chemistry acquired a strict quantitative nature allowing reliable predictions to be made. 1800 AD: Joseph Proust discovered the law of definite proportions which states that in chemical reactions, elements always combine in small whole number ratios to form compounds. At the same time, Alessandro Volta produced the first chemical battery which was the initial manifestation towards the theory of electrochemistry. 1803 AD: John Dalton published his Atomic Theory which stated that all matter is composed of particles called atoms, these being very small and indivisible. Amadeo Avogadro and Ludwig Boltzmann favoured Dalton’s Atomic Theory and made great advances in explaining the behaviour of gases. 1820 AD: Michael Faraday made a great contribution towards the science of electrochemistry by proposing quantitative laws that determine the quantity of electricity needed for deposition of a certain mass of an element and how fixed quantities of elements are deposited in specific ratios by the same quantity of electricity. 1854 AD: Heinrich Geissler created the first vacuum tube. 1870 AD: Dmitri Mendeleev together with Lothar Meyer developed the Periodic Table and used it to predict the properties of certain yet unknown elements like germanium, gallium and scandium. 1879 AD: William Crookes made headway in modern atomic theory when he used the vacuum tube made by Heinrich Geissler to discover cathode rays. Crookes created a glass vacuum tube which contained a zinc sulfide coating on the inside of one end, a metal cathode embedded in the other end and a metal anode in the shape of a cross in the middle of the tube. When a potential difference was applied between anode and cathode, an image of the cross appeared and the zinc sulfide glowed. Crookes hypothesized that there must have been rays coming from the cathode which caused the zinc sulfide to fluoresce and the cross to create a shadow. These rays he called cathode rays. 1885 AD: Eugene Goldstein discovered the proton while using a glass tube filled with hydrogen gas. He discovered that the proton had a charge equal and opposite to the electron. He also found out that the mass of a proton is 1836 times the mass of the electron. 1895 AD: Wilhelm Roentgen accidentally discovered X-rays while experimenting with cathode rays. While doing research on cathode rays in a dark room, Roentgen noticed that a bottle of barium platinocyanide was glowing on a shelf. He discovered that the rays that were causing the fluorescence could also pass through glass, cardboard and walls. 1896 AD: Henri Becquerel was studying the fluorescence of pitchblend (an ore containing a high proportion of zinc sulfide) when he discovered that pitchblende gave a fluorescent light with or without the aid of sunlight. 1897 AD: J.J. Thomson placed a strong magnetic field in the vicinity of a cathode ray tube, like the one made by Crookes in 1879. He concluded that cathode rays are negatively charged and even found ways to measure the magnitude of each negative charge. Through more experiments, he discovered that all atoms contain this negative charge which he renamed electrons. Thomson’s atomic model constituted a sphere of positively charged material with negative electrons stuck into it. Also in 1897, Marie Curie while experimenting with pitchblend found that the impurities contained in this compound, mostly uranium and thorium, emitted haphazard radiation. She soon discovered two previously unknown elements which she named radium and polonium and which also emitted the same type of radiation. 1909 AD: Robert Millikan discovered the mass of an electron by introducing charged oil droplets into an electrically charged field. 1911 AD: Ernest Rutherford placed radioactive sources (those discovered by Marie Curie, that is uranium, thorium, radium and polonium) in an electric field. Some of the radiation emitted was deflected to the positive plate; some of it was deflected to the negative plate while the rest travelled on undeflected. Thus, he concluded that there are three types of radioactive radiations which he named alpha (+), beta (-) and gamma (neutral). By performing other experiments, Rutherford created an atomic model different from Thomson’s sphere. Rutherford was of the opinion that the atom was mostly empty space. It contains an extremely tiny dense positively charged nucleus (full of protons) and this nucleus is surrounded by high speed electrons. Niels Bohr’s study about the atom was in full agreement with Rutherford’s theory. 1914 AD: Henry Moseley made several attempts to determine the number of protons in the nucleus of each atom. He was unsuccessful since the neutron had not yet been discovered. 1932 AD: James Chadwick discovered the neutron. Enrico Fermi bombarded atoms of certain elements with neutrons and produced elements of the next highest atomic number. Nuclear fission occurred when Fermi bombarded uranium with neutrons. 1934 AD: Irene Curie and Frederic Joliot-Curie found out that more radioactive elements could be created artificially in the lab with the bombardment of alpha particles on certain atomic nuclei. 1940 AD: America embarks on the Manhattan Project to produce the first working nuclear fission reactor. The most prominent contributors for this project were Albert Einstein and Enrico Fermi. Modern Chemistry: The first part of the 20th century saw a huge increase in the exploitation of petroleum extracted from the earth for the production of a host of chemicals. Large scale production and refinement of petroleum produced liquid fuels such as gasoline, diesel, solvents, lubricants, asphalt, waxes and hundreds of other synthetic materials like plastics, paints, detergents and adhesives. Many of these required new catalysts and the utilization of chemical engineering for their cost-effective production. Today’s chemical discoveries and the theories that explain them are mostly centred around the electronic structure of the atom. Linus Pauling’s work about The Nature of the Chemical Bond is concerned with the principles of quantum mechanics from which he succeeds in deducing the angles between atoms in large molecules and how these angles effect the rate of chemical reactions. The science of biochemistry has also made great steps forward when James Watson and Francis Crick deduced the double helical structure of DNA using X-ray diffraction patterns. Also during the last decade of the 20th century, Miller-Urey demonstrated that simple amino acids are the basic constituents of protein and so the building blocks of living things. It is obvious from this historical Chemistry background that the knowledge of Chemistry has changed substantially through the ages. The experience acquired by chemists was no longer pertinent to the study of the whole nature of matter but only to aspects related to the electrons surrounding the atomic nucleus. The study of Chemistry is nowadays restricted to the nature of matter around us where the conditions of temperature, pressure and electromagnetic radiations pertain to normal circumstances. Chemistry was therefore redefined as the science of matter that deals with the composition, structure and properties of substances (elements, compounds, mixtures, alloys, ores etc) and the transformations that they undergo.
Posted on: Thu, 15 Aug 2013 15:59:19 +0000
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