Category Great Scientific Discoveries

          John Dalton, J.J. Thomson, Ernest Rutherford, and Niels Bohr were the scientists who made notable contributions towards the study of atomic structure.

          Dalton successfully stated about atoms, but failed to identify the subatomic particles. Sir Joseph John Thomson came up with a model of an atom in the 1900s. He described atom as a positively charged sphere into which negatively charged electrons were embedded. Thomson’s model can be visualised as a plum pudding with the positively charged atom and plum pieces as electrons. Thus, the idea came to be called the ‘plum pudding model.’

          Rutherford was J.J. Thomson’s student. He modified his teacher’s model when another subatomic particle called nucleus was discovered.

          Neils Bohr put forth his model of the atom in 1915. One of the most significant ideas he suggested was that electrons were placed on distinct ‘stationary orbits’ inside the atom.

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          Proton is one of the constituents of an atom, besides neutron and electron. These positively charged protons reside in the nucleus of the atom and add to the overall positive charge of a molecule.

          Ernest Rutherford is generally credited with the discovery of protons. He discovered alpha and beta ‘rays’ from uranium in 1899. The alpha rays were later found to be from the nuclei of helium atoms. In 1919 Rutherford conducted many experiments to explore radioactivity. As a result of one of these experiments, he discovered that atoms have a concentrated positive centre charge which contains most of the mass of that atom.

          Rutherford suggested that the nucleus carried a positively charged particle. He called it proton; a name derived from the Greek word ‘protos’ which means ‘first’. The numbers of protons differ from one element to another thereby giving each nucleus a different charge. This meant that the hydrogen nucleus, which has a single proton, was an elementary particle.

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          Noble gases are a group of chemical elements with similar properties. Six naturally occurring noble gases are helium, neon, argon, krypton, xenon and radioactive radon. As we saw before, helium was first discovered in 1868, while looking at the chromosphere of the Sun and was first isolated by William Ramsay.

          Argon, the lazy one, was discovered by Lord Rayleigh and William Ramsay at University College, London in 1894. It was named so, due to its inert character. Krypton, neon, and xenon were discovered by William Ramsay in 1898. Radon was first identified in 1898 by Friedrich Ernst Dorn. However, it was not considered a noble gas until 1904 when its characteristics were found similar to other noble gases.

          In 1904, Rayleigh and Ramsay received the Nobel Prizes in Physics and in Chemistry respectively for their discovery of the noble gases.

          As these gases occur in smaller amounts in the atmosphere, they are also called rare gases. Helium is found sealed within some of the radioactive minerals and can be released on heating. Others are obtained by fractional distillation of liquid air.

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          Helium was first discovered in the corona surrounding the Sun and later found in gases leaking from Mount Vesuvius. It is the second-most abundant element in the universe.

          The first evidence of helium was observed on 18 August 1868, in the spectrum of the chromosphere of the Sun. It was discovered on Earth much later. Italian physicist Luigi Palmieri detected helium on Earth for the first time through its spectral line in 1881. He found it while analysing a material that had sublimated during a recent eruption of Mount Vesuvius. The first person to isolate helium on Earth was the Scottish chemist, Sir William Ramsay. On 26 March 1895, he heated a mineral called cleveite, which contains uranium and discovered that it gave off a gas. The gas was identified by the yellow line in its spectrum, which matched that of the helium in the Sun.

          The same year, chemists Per Teodor Cleve and Abraham Langlet in Uppsala, Sweden collected enough helium to determine its atomic weight accurately. Later, Ramsay and a British chemist Frederick Soddy discovered that helium is produced whenever radioactive elements decay.

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          Silicon is an element represented as Si. Sir Humphry Davy proposed the name “silicium” for silicon after an attempt to isolate it in 1808.

          In 1811, Gay-Lussac and Louis Thenard are thought to have prepared impure amorphous silicon by heating recently isolated potassium metal with silicon tetrafluoride. They however, did not purify the product, nor did they identify it as a new element. Silicon’s present name was given in 1817 by Scottish chemist Thomas Thomson.

          Jons Jacob Berzelius is credited with the discovery of silicon. In 1824, he used the method followed by Gay-Lussac to prepare amorphous silicon and then purified the product into a brown powder through repeated washing.

          Silicon of lesser purity is used in metallurgy as a reducing agent and as an alloying element in steel, aluminium, brass, and bronze.       

          Silicon dioxide (silica) and various silicates are the most important compounds of silicon. Silica in the form of sand and clay is used to make concrete and bricks. It is also used as refractory material for high-temperature applications.

 

          The fact that blood circulates in our body might seem obvious to us in this age of advanced medical technology, but that was not always the case. Early knowledge of this subject came from the studies of Galen, the Greek physician. Unfortunately, most of his conclusions were later proven wrong.

          It was William Harvey who discovered and published the first accurate description of the human circulatory system in 1616. Before Harvey’s discovery, it was thought that blood was made in the liver which later turned into flesh. Though this might seem stupid to us, it was widely accepted by the doctors back then.

          Harvey accepted only those ideas which had scientific evidence. He finally published his research findings in Exercitatio Anatomica de Motu Cordis Sanguinis in Animalibus (An Anatomical Exercise on the Motion of the Heart and Blood in Living Beings) in 1628. He proved that blood circulates within the body and that the circulatory system includes arteries, veins and the heart.

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