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Evolution and development of the periodic table.

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Introduction

Evolution and development of the periodic table: First efforts to classify elements came in the publication 'Trait� El�mentaire de Chimie' (Treatise on the Chemical Elements), published in 1789 by Antoine Lavoisier3. The 33 known Elements were separated as gases, metals, non-metals and earths. In the 19th century elemental discovery led to further efforts, with valency being a favoured sorting method. However, D�bereiner was first to sort elements by their weight/mass. He arranged elements to fit triads of similar properties, but also mass - each middle element had a weight equal to the average of the first and third. British chemist, Newlands, in 1863 formed the 'law of octaves' - every eighth element had similar properties. Newlands table, hindered by the noble gases remaining elusive - lacked organisation with elements sharing spaces, due also to inaccurate mass measurement1. The next major effort came from Dimitri Mendeleev helped by Stanislao Canizzaro, who, in 1958 clarified mass numbers for 65 known elements, allowing Mendeleev to arrange them into rows according to mass and columns of similar valency. ...read more.

Middle

Figure 2: (B) Gallium unusually forms multiple chlorides, which involve dative covalent bonds, rarely seen in metallic compounds (they are normally ionic). Also, Gallium's reactivity in both acids and alkalis is also characteristic of non-metals. This occurs as Gallium forms amphoteric hydroxides, which is a rare property1: 2Ga(s) + 6H+(aq) 2Ga3+(aq) + 3H2(g) 2Ga(s) + 2OH-(aq) + 6H2O(l) 2[Ga(OH)4]-(aq) + 3H2(g) Furthering our knowledge of atomic structure using spectroscopy and the UNILAC particle accelerator: In 1899, Ernest Rutherford proved the existence of sub-atomic particles when he proved a dense nucleus existed at the centre of atoms. He proved that this nucleus, in opposition to electrons, was dense and had a positive charge2. Chemists, such as Bohr, quickly capitalised on this discovery and in 1913, he published his theories regarding atomic spectra, refining Rutherford's idea of orbitals about a nucleus and proposing defined energy levels for electrons. Emission spectra are produced by exciting electrons with an electrical arc, then allowing electrons to drop to lower energy levels and emit additional energy in the form of photons. ...read more.

Conclusion

It is therefore believed that synthesising element 114 will contribute greatly to knowledge of the sub-atomic particles and their relation to isotopic/nuclear stability. From discovery to synthesis: Previously, chemists worked to discover elements as it was the most active area for chemical breakthroughs This was due to initiatives that allowed chemists to recognise properties, such as spectroscopy3. The likes of Mendeleev, in ordering the elements and predicting new ones, also promoted new discovery. Yet, recently, emphasis has been on the purpose of elements. Scientists have abandoned the discovery of natural materials and begun searching for synthesised alternatives. As elemental properties become more predictable, they become increasingly desirable and thus their synthesis more urgent. This was shown in the Cold War, where American and Russian scientists competed to produce more radioactive isotopes for use in weapons. Particle accelerators, such as the UNILAC have been pivotal in the formation of heavier elements and are seen as vital in achieving what is often referred to as 'the holy grail of elements' - element 114, which would lead to breakthroughs in knowledge about atomic structure and stability2. Such efforts to create new elements have labelled particle chemists: 'the new alchemists'(H). NAME: COWLIN, Robert CANDIDATE NUMBER: 8118 1 ...read more.

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