The atomic emission spectrum of gallium (2)
De Boisbaudran determined some of its properties. They were then compared alongside Mendeleev’s predictions.
A table showing Mendeleev’s predictions of gallium, with its actual properties (3)
The table shows that Mendeleev was correct in his predictions and this supported his ideas well. (259)
The properties of gallium are considered unusual for many reasons. The element has a melting point of 29.78°C, so in some countries it is a liquid, and in others it is a solid. Gallium also has a very high boiling point of 2403°C. Because of this and its low melting point, “it has the widest liquid range of any element” (4). Also, it is denser as a liquid than it is as a solid, such as water. Because of certain properties, gallium can be seen as a metal. It is similar to aluminium, a metal and other metals surrounding it in the table. Gallium dissolves in both acids and alkalis, so they have “amphoteric hydroxides” (5).
2Ga(s) + 6H+(aq) 2Ga3+(aq) +3H2(g)
A reaction between gallium and hydrogen ions (6)
2Ga(s) + 2OH-(aq) + 6H2O(l) 2[Ga(OH)4]-(aq) +3H2(g)
A reaction of gallium with hydroxide ions (7)
Gallium also forms dative covalent bonds, like metals do and has low melting points. For instance gallium chloride has a melting point 0f 77°C.
The bonding in Ga2Cl6 (8)
Gallium can be seen as a non-metal as it has a melting point of 29.78°C and so in some places of a warmer climate, the temperature will be beyond its melting point and so gallium would be a liquid. Gallium is seen being used in high temperature thermometers which would again suggest that gallium is a liquid. (452)
Discovered in the 19th century, at around 1860, atomic spectroscopy uses an atomic emission spectrometer to excite atoms using an electric arc. “The excited atoms emit light which can be split by a prism to show the emission spectrum for the sample as a series of bright lines on a black background” (9). Using atomic spectroscopy helps increase our knowledge about elements in the periodic table as any new lines found in a spectrum of a sample represent a new element as each element has its own unique emission spectrum. Because of this, using atomic spectroscopy proved to be a very good method of discovering new elements. This method relies on an understanding of the structure of atoms as when an electron moves to a lower level in an element, it emits a photon of electromagnetic radiation. “This radiation is usually in the infrared, visible or ultraviolet regions” (10). The energy of this photon is the difference between the two energy levels. “The frequency of the radiation emitted is given by E=hv” (11). The lines in an emission spectrum correspond to the frequencies of radiation that are given out.
The UNILAC accelerator, also known as the Universal Linear Accelerator works by firing a beam of heavy ions at a fast speed from an accelerator towards a rotating disc of the target metal. If this works then new elements are formed which are then separated and detected. This process began in the 1980s and first became successful in 1981 when element 107 was created.
24Cr + 83Bi 107Element (12)
The reaction using the UNILAC showing the creation of element 107
This helps increase our knowledge of the periodic table as new elements continue to be found using this method of detection. However, the rate at which they are being found is decreasing greatly. There is always room for more elements to be put into the periodic table and the UNILAC accelerator will try to continue to find them. The use of the UNILAC accelerator relies on an understanding of the structure of atoms as heavy ions are used in this process and so knowledge of how the electrons behave is essential to the alchemists carrying out the procedure as this is how new elements are formed. (809)
The original periodic table was arranged by increasing atomic weight and developed through time from Johann Döbereiner’s series of triads, through to the Law of Octaves, created by John Newlands until Dimitri Mendeleev produced the best version of the periodic table, amending incorrect data values and predicting what were, at the time undiscovered elements. In the 19th century most of the elements discovered were found using atomic spectroscopy, used by Paul Emile Lecoq de Boisbadran, to name but one. Now, in the 21st century, slight amendments have been made to the periodic table originally created by Mendeleev. The biggest change probably being the addition of the noble gases which were hard to discover as they are inert. Since then, more elements have been added to the table and they are now arranged by increasing atomic number instead of relative atomic mass. New elements are still being found and now, the most common method is by using the UNILAC accelerator. (968)
References
- http://fccjmail.fccj.org/~ethall/period/period.htm
- Woods G. 2001
Gallium: a landmark in the history of chemistry. Chemisty Review. Fig 4
- Woods G. 2001
- Gallium: a landmark in the history of chemistry. Chemisty Review. Table 1
- Woods G. 2001
Gallium: a landmark in the history of chemistry. Chemisty Review.
- Woods G. 2001
Gallium: a landmark in the history of chemistry. Chemisty Review.
- Woods G. 2001
Gallium: a landmark in the history of chemistry. Chemisty Review.
- Woods G. 2001
Gallium: a landmark in the history of chemistry. Chemisty Review. Fig 6
- Woods G. 2001
Gallium: a landmark in the history of chemistry. Chemisty Review.
- Burton G., Holman J., Lazonby J., Pilling G., Waddingtion D.
Salters Advanced Chemistry – Chemical Ideas. Heinemann. p124
- Matthews R.
The New Alchemists. Chemistry Review.
- Matthews R.
The New Alchemists. Chemistry Review.
Other Sources
Burton G., Holman J., Lazonby J., Pilling G., Waddingtion D.
Salters Advanced Chemistry – Chemical Storylines. Heinemann.
http://www.chemsoc.org/viselements/pages/history.html
http://www.goodfellow.com/static/A/GA00.html
