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The Development of the Periodic Table

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Introduction

The Development of the Periodic Table In the early 19th century many chemists began to develop their knowledge of analytical chemistry, the classification of compounds, and it soon came necessary to classify the elements. Johan D´┐Żbereiner showed in 1817 that atomic weight of strontium lies approximately between that of calcium and barium and that these element showed a number of similar properties and thus should be grouped. He and other leading chemists later went on to show how this was also true for the halogens and the alkali metals. In 1863 John Newlands showed that when the elements were arranged in order of atomic weight every eighth element showed familiar traits and thus a table idea was brought up. He considered that some elements had not been invented so he left gaps to fit his idea however after about 20 elements the table became inaccurate. In 1869 Dimitri Mendeleyev did extensive research to traits of elements, especially valency, and developed his own table which left gaps for undiscovered elements. ...read more.

Middle

Gallium will also alloy with most metals to create low-melting alloys and good liquid alloys to use in thermometers. More recently gallium has been used in doping semiconductors, producing solid-state devices such as transistors and gallium arsenide is a key component of LEDs. Unusually for a metal, gallium is denser as a liquid then as a solid, like water. The chemical properties of gallium are much the same of aluminium, above it in the periodic table, as Mendeleyev predicted. They both dissolve in both acids and alkalis which is unusual for a metal. The reactions of gallium and aluminium with an acid and an alkali are shown below showing that aluminium and gallium behave in identical ways. Acid (H+ ions) 2Al(s) + 6H+(aq) --> 2Al3+(aq) + 3H2(g) 2Ga(s) + 6H+(aq) --> 2Ga3+(aq) + 3H2(g) Alkali (OH- ions) 2Al(s) + 2OH-(aq) + 6H2O(l) --> 2[Al(OH)4]-(aq) + 3H2(g) 2Ga(s) + 2OH-(aq) + 6H2O(l) --> 2[Ga(OH)4]-(aq) + 3H2(g) After the discovery of gallium many scientists went to work at discovering new elements to fill in gaps in Mendeleyev table however a greater understanding of the elements was required and an understanding of the structure of atoms. ...read more.

Conclusion

It has now become a challenge for scientists to synthesise new elements. When a large element is bombarded by a smaller element travelling at a very fast speed the two nuclei may fuse together to form a new element with the combined amount of protons. Here is a diagram and the equation of two nuclei fusing together: This method has found many of the new elements since 1965. However as the elements get bigger the nuclei needed greater violence between them to persuade them to react. The result of this process is a radioactive element that usually decays quickly and so most of the elements are useless however due to trends in known elements there are certain elements that are very stable that appear in the table at sensible points. Scientists believe that ununquadium-298 (114 protons) will be stable and will be very valuable. To create heavier elements requires accelerating the nuclei very fast which is currently done by GSI with a universal linear accelerator (UNILAC) into a rotating disc of target metal and the decay can then be analysed to determine what element has been produced. ...read more.

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