In 1863, English chemist John Newlands wrote of his discovery about the law of octaves. Charting the 62 known elements in order of mass, he noticed the repeated physical and chemical properties of each, every eighth element (the noble gases were yet to be discovered). Thus, creating the ‘first’ periodically listed table of elements.
In 1869, Russian scientist Dimitri Mendeleev also arranged the elements by atomic weight and their properties. During 1871, he revised his original 17-group table, into 8 columns, of which the eighth were transition elements. Not only did Mendeleev’s periodic table comprise of Dobereiner’s law of triads, but also showed relationships between elements horizontally, diagonally and vertically. Although still incomplete, from his table he could leave gaps where he predicted elements would appear. The modern periodic table has changed little since 1871, except now being in order of atomic number, the addition of new elements and the eighth column being named the noble gases.
The major boost towards Mendeleev’s table was the discovery of Gallium, by French scientist Paul Emile Lecoq de Boisbaudran in 1875. The similarity between Mendeleev’s prediction (of which he named eka-aluminium) and Gallium were amazing. The only property of which the Russian differed upon was its density. Mendeleev asked Lecoq to check his results again, and after further purification, matched almost exactly with his prediction. Over the next 10 years two more missing (but predicted) elements were found, both a further boost to Mendeleev’s periodic table.
Gallium itself is considered to be a very unusual element. Its physical properties suggest it to be that of a non-metal, and if so, very similar to that of the liquid metal mercury. Its melting point is very low (29.78°C), so in many warm climate countries, is a liquid. Scientists are yet to discover a reason for this. Because of this, and its extremely high boiling point (2403°C), Gallium has the highest liquid range of an element, though this is useful in the production of high temperature glass thermometers. Gallium, also shares with water, the property of being denser as a liquid than that of a solid, again something uncommon of a metal.
Although very few metals behave this way, other than aluminum, gallium dissolves in both acids and alkalis, evolving hydrogen. This shows its resemblance as a metal to another, but also it can be seen as though it is a non-metal.
Since Mendeleev’s discovery, technology has developed. Atomic spectroscopy shows upon a spectrum, the energy being absorbed or emitted by an element, enabling scientists to identify new or already discovered elements. Each element appears on the spectrum according to its frequency. The absorption method identifies elements upon the missing lines in a spectrum. Radiation is absorbed by elements at different frequencies, the elements or shown as black lines upon otherwise continuous spectra, where this radiation has been absorbed. The emission spectra works in almost the opposite way. When an atom absorbs electromagnetic radiation, its energy state increases to what is called its excited state. This was discovered in the Quantum theory and new information on the structure of an atom. Originally atoms themselves were considered to be the smallest building blocks of matter. However, Ernest Rutherford proved that “each atom contains a dense, positively charged nucleus”. From this, in 1913, Neil Bohr published his research into the emission spectra, writing about how electrons lived within atoms, where is depended upon their energy states. It emits this absorbed photon energy when the electron falls to a lower level again, as radiation. Thus, an emission spectra is produced enabling scientists again to identify elements coinciding with the frequency shown on the spectrum.
The Quantum theory suggested that, like electrons, the nucleus also has shells containing neutrons and protons. Where as electrons would fill their rings to become noble gases, shells within the nucleus would fill to become extremely stable. Elements with filled shells within the nucleus are said to have ‘magic numbers’. This is because they are stable against radioactive decay. Although element 113 has just been discovered, scientists note that element 114 would be the next ‘magic numbered’ element. This has made chemists all over, eager to synthesize this element. This is done by “firing beams of metal ions into metal targets in an attempt to persuade the nuclei to fuse together to form new elements”.
In an attempt to reach the ‘most wanted’ element, 114, the GSI center produced the UNILAC accelerator. This fired beams of relatively heavy ions towards a rotating disk of a heavy, stable element (such as lead). The UNILAC itself is a 120 m long linear accelerator, which brings the ions on track and accelerates them to 20 % of the velocity of light. This beam can also be further accelerated to help the matter (up to 90% the speed of light) in the heavy ion synchrotron (SIS). The violence, of which this is done, overcomes the natural repulsion of the nuclei and fuses together the elements to form a new element. This has successfully worked, and centers across the world have now produced the ‘magical’ element, 114.
Bibliography:
Websites:
http://web.fccj.org/~ethall/period/period.htm
Basic information about the development of the periodic table and portrait pictures of the chemists.
http://www.aip.org/history/curie/periodic.htm
Website listing information about Dimitri Mendeleev and his periodic table, and also the modern day table.
http://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&oi=defmore&q=define:Periodic+table
Definitions of the periodic table.
http://www.gsi.de/portrait/beschleunigeranlage_e.html
Information on GSI and that of the UNILAC accelerator.
Books:
Chemical Storylines: Heinemann – The Central Team
Where do chemicals come from? Pages 12-14
Information on spectroscopy.
Chemistry Open Book Paper:
Article 1: Chemistry Review, 2001, Volume 11, Number 2: Gordon Woods
Gallium: a landmark in the history of chemistry
Gallium and its history
Article 2: Chemistry Review, 1999, Volume 9, Number 1: Robert Matthews
The New Alchemists
Information on synthesising new elements
