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The Periodic Table

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The Periodic Table was developed in stages; the first person that attempted to classify elements in relation to their atomic mass was Johann D�bereiner. D�bereiner noticed similar properties between known elements. Theses similarities occurred in groups of threes and were known as 'triads'. The atomic weight of the middle element in each triad is approximately an average of the others. In 1863 John Newlands put the known elements in order of atomic weight and noticed that every eighth element had similar properties, he called this the Law of Octaves. After about 20 elements the table became ragged and some elements had identical places whilst others were incorrect because of inaccurate weights. Furthermore Newlands left no gaps for any unknown elements. Dimitri Mendeleev amended some atomic weight values and left gaps for any undiscovered elements. Mendeleev predicted properties of five elements that should be discovered, within 15 years of his predictions three of these elements had been discovered. One of the unknown elements was called Eka-aluminium today known as Gallium. ...read more.


Gallium dissolves in acid and alkalis developing hydrogen, the equations represent reactions of both elements with hydrogen ions and consequently show the similarity between their properties. 2Al(s) + 6H+ (aq) 2Al3+ (aq) + 3H2 (g) 2Ga(s) + 6H+ (aq) 2Ga3+ (aq) + 3H2 (g) The only difference in the above equations is the symbols for the elements. Below are two equations showing that the elements respond the same in other chemical reactions. 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) The reaction stated above is between the elements in discussion and hydroxide ions, again the only difference is the symbol for the element. So far the chemical properties that have been discussed suggest that gallium is a metal as they are identical to the properties of aluminium. (1+7) Atomic spectroscopy has been used successfully to detect the existence of unknown elements. An atomic emission spectrometer is used to stimulate atoms using an electric arc causing the atoms to absorb energy. ...read more.


30Zn + 82Pb 112Element The picture below represents a 3D map of the known isotopes. The white columns (220 words) show stable nuclei found naturally. The orange network represents the radioactive isotopes that undergo �-decay. The yellow on the map denotes isotopes that undergo spontaneous fission, whilst the red area demonstrates ?-decay. The small red column at the bottom of the map shows element 112. A three dimensional map of the known isotopes Despite successes with the UNILAC accelerator it became increasingly harder to produce atoms of new elements. (2+4) Two hundred years ago it was the intention of scientists to discover new elements, today the focus of research is to synthesise new elements. There are only 92 naturally occurring elements, hydrogen to uranium; however the periodic table shows 106. A reason for this difference is because of modern apparatus and theoretical research. The increase in theoretical research extends the knowledge of scientists providing a clear idea of the formation of atoms and elements. This information has meant they have been able to put their knowledge into practice, testing their ideas and techniques. Providing their research is sound then they may be able to create the conditions and environment required to produce new elements. ...read more.

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