Newlands left no gaps in his table for any elements that were yet to be discovered, because of this he resorted to putting more than one element in one space. e.g. Cobalt & Nickel and Platinum & Iridium.
In 1869 Russian chemistry professor Dimitri Mendeleev published his table of periodic law – The properties of the elements are a periodic function of their atomic weights5. Mendeleev’s approach to classifying the elements differed from that of his predecessors in that he devised a theory from which he could predict with some precision the properties of elements which were unknown at the time. The discovery of Gallium provided strong evidence to suggest that Mendeleev’s table of periodicity was accurate.
Gallium is a soft silvery metal in group three of the periodic table. An example of the unusual properties of gallium are the melting and boiling points. Gallium melts at 29.78°C (slightly above room temperature) and boils at 2403°C. This very low melting point and exceptionally high boiling point give Gallium the longest liquid range of any element. Gallium is a liquid at room temperature, which suggests it lies between non-metals which are usually in the gases state at room temperature and metals which are usually in their solid state are room temperature.
Like aluminium, gallium dissolves in both acids and alkalis. As demonstrated by the chemical equations above. The few metals which react with both acids and alkalis all have amphoteric hydroxides. These are hydroxides which demonstrate acidic and basic properties since they react with both acids and alkalis. Gallium is denser as a liquid than a solid therefore the solid floats on the liquid, much like ice floats on water. The explanation is assumed to be similar to that of water, the solid having a more open structure than the liquid. The covalent bonds gallium forms with chlorine to form the anhydrous trichloride of gallium are characteristic of a non-metal as metals tend to form ionic bonds with non-metals.
The discovery of new elements was assisted by the discovery of atomic spectroscopy around 1860. by using an atomic emission spectrometer scientists can excite atoms using an electric arc, the excited atoms of the sample emit light which can be split by a prism to show the samples emission spectrum. Every element has a different emission spectrum, a new line or lines within an emission spectrum meant the discovery of a new element.
Atomic spectroscopy relies on the comprehension of the quantum theory – the concept that electrons exist in orbits of different energies around the nucleus – the dense, positively charged centre of an atom10.
After the naturally occurring elements had been discovered scientists began investigating the possibility of synthesising elements with higher atomic weights than those of the naturally occurring elements. Armbruster and his colleagues at the Heavy Ion Research Centre (GSI) use a UNILAC accelerator – this entails firing a beam of relatively heavy ions from an accelerator towards a target of a heavy, stable element, if this is done with sufficient violence, the ions overcome the natural repulsion of nuclei and fuse together, creating a new element11. The synthesising of these elements relies on Ernest Rutherford’s 1899 model of an atom. In his model he proposed that atoms encompass a dense, positively charged nucleus. If atoms didn’t comprise this dense centre of positive charge, it would be impossible for new elements to be synthesised because there would not be two nuclei to fuse together and the atoms would pass through each other with little or no effect on one another.
Once chemists had discovered all of the naturally occurring elements, they deviated toward synthesising new elements which had larger atomic weights than the naturally occurring elements by a whole range of different methods. The UNILAC accelerator is an example of a method of synthesising elements. The work of chemists has progressed over the last two hundred years from discovering elements and the complex task of producing a method of classifying these elements to the synthesising of elements with atomic weight beyond those found in nature. The progression of chemists work has been influenced by many individuals along the way, without the work of Dimitri Mendeleev we would not have the periodic table which is one of the key foundations of chemistry. Chemists have been working on the periodic table and elements for over two hundred years and there is no evident end in sight.
“You’ll all ways find people who’ll say, ‘Let’s try once more’,” Armbruster 12
Bibliography
1. History, The Law of Triads, http://www.chm.bris.ac.uk/webprojects2000/atrim/history.htm
2. Online Encyclopaedia – Periodic Table, http://www.yourencyclopedia.net/Periodic_Table.html
3. History, The Law of Octaves, http://www.chm.bris.ac.uk/webprojects2000/atrim/history.htm
4. An Extract from Chemical News, March 1866, Heinemann, Salters Advanced Chemistry, Chemical Storylines, August 2000
5. Genesis, A historic Overview: Mendeleev and the Perioric Table, http://www.genesismission.org/educate/scimodule/UnderElem/UnderElem_pdf/HistOverST.pdf
6. Table 1, Article 1, OCR Open-Book Paper
7. Unusual properties of gallium, Article 1, OCR Open-Book Paper
8. Fig. 6 Bonding in Ga2Cl6, Unusual properties of gallium, Article 1, OCR Open-Book Paper
9. Fig.3, Article 1, OCR Open-Book Paper
10. Box 1, Article 2, OCR Open-Book Paper
11. The UNILAC accelerator, Article 2, OCR Open-Book Paper
12. Success Story, Article 2, OCR Open-Book Paper
