Table showing Mendeleev’s Periodic Table
Today the periodic table is arranged by atomic mass, which can be defined as the number of electrons an element possesses. This is unique for each element and therefore ensures that there is no modifying the order of elements, which was not so with Mendeleev’s table (iodine and tellurium were placed the wrong way round). Today’s Periodic Table looks like this.
Diagram showing the Modern Day Periodic Table
Unusual Properties of Gallium
Physical Properties
Gallium has three main unusual physical properties. It has a low melting point of just under 30*c. This means that the bonds within its metallic structure are weak. As a result only a small amount of energy is needed to be put in to make it melt.
On the other hand gallium has a boiling point of 2403*c, giving it the largest liquid phase range of an element. This may be due to the fact that gallium’s intermolecular forces give it added strength, so more energy must be put in to break these bonds. If gallium is a diatomic element, then the instantaneous dipole-induced dipoles that form between molecules means more energy is required to give the molecules sufficient energy to overcome one another’s attractive forces. Below is diagram showing this.
Diagram showing how a molecule can become polarised and form dipoles
Metal or Non-Metal/ Chemical Properties
Gallium also has some interesting chemical properties. It dissolves in both acids and alkalis, which is very rare. It therefore shows it has both basic and acidic properties. This is also true for aluminium which lies in the same group as gallium. The equations below show that gallium (and aluminium) can both be defined as having amphoteric hydroxides.
Reactions of aluminium and gallium with hydrogen ions
2Al(s) + 6H+(aq) 2Al3+(aq) + 3H2(g)
2Ga(s) + 6H+(aq) 2Ga3+(aq) + 3H2(g)
Reactions of aluminium and gallium with hydroxide ions
2Al(s) + 20H-(aq) + 6H2O(l) 2[Al(OH)4]-(aq) + 3H2(g)
2Ga(s) + 20H-(aq) + 6H20(1) 2[Ga(OH)4]-(aq) + 3H2(g)
As well as this gallium also forms covalent bonds, which only occurs with non-metals. This can be seen in the anhydrous trichloride of gallium. This suggests that it is a non-metal. This is shown in the diagram below
Diagram showing the Covalent Bonding in anhydrous tricholride of Gallium
However is has only three electrons in its outer shell, so to form a full outer shell gallium’s simplest path of action would be to lose 3 electrons than to gain 5 electrons. This therefore suggests it is a metal.
For these reasons gallium is often described as a strange element due to the unique chemical and physical properties it possesses.
Atomic Spectroscopy
The atomic spectrum of an atom allows us to understand chemical elements in more detail. Below is shown the emission spectrum of hydrogen.
Diagram showing the emission spectrum of hydrogen
Hydrogen’s one electron will remain at ground state until excited, due to it absorbing energy
Energy levels are quantised so electron absorbs or emits fixed amounts of energy when moving between shells
The diagram helps us to realise that the electrons within an atom can only exist in certain energy levels, and when the electrons do not posses energy, in the form of photons of radiation, exist in a ground state. To interpret these results you must therefore understand that each atom is unique, meaning it has different quantised energy levels.
As well as this we can understand how the atom will react when it comes into contact with another. For a metal to lose an electron, the electron must have sufficient energy to overcome all of the energy levels. This is more often known as the activation energy. It is therefore clear why energy is needed to be put into a reaction. For this reason atomic spectroscopy has greatly aided us into understanding how the electron works.
We can therefore explain trends found in the periodic table. Two elements which have the same number of electrons in their outer shells will react in a similar way, as they both need to gain/lose the same number of electrons.
Changing Work of Alchemists
Over the last two hundred years there have been significant changes in what alchemists now do. The nineteenth century saw the main focus on discovering elements and thinking how to classify elements. Mendeleev was particularly important for the classification of the known elements, whilst others, such as Paul Emile Lecoq who discovered gallium, worked to complete the periodic table which was being established.
Today the main focus of alchemists is to synthesis new elements. This is done by firing beams of metal ions into metal targets in order to encourage the nuclei to fuse, and thus creating a new element. This is done using a UNILAC Accelerator.
Diagram showing the stages of gold and nickel nuclei fusing together to form bohrium
Gold nuclei (79 blue protons)
Nickel nuclei (28 red protons)
Nickel ions are fired onto a rotating disc of the target metal (gold in this case).
Nickel ions are fired with enough speed to overcome the repulsion of the nuclei
The two elements have now fused together to form bohrium
In these ways the UNILAC accelerator has been very useful in synthesising new elements, and shows us how alchemists are now using advanced techniques to discover new elements as opposed to two hundred years ago when much was done by simpler reactions- e.g. displacement and (later) electrolysis.
Bibliography of Sources
Internet Sites
Open Book Paper
- Article 1, Page5, Table 1 – Comparisons between Mendeleev’s predictions of gallium and its actual properties
- Article 1, page 6 – Reactions of aluminium and gallium with hydrogen ions
- Article 1, page 5, figure 3 – Atomic spectrum of hydrogen
- Article 2, figure 4, page 2 – Nickel and Gold Nuclei fusing together
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Article 1, figure 6, page 5 – Bonding in Ga2Cl6
Other Sources
- Salters Advanced Chemistry; Chemical Ideas 5.3 page 98 figure 18 – Dipoles formed in Xe atoms
- Salters Advanced Chemistry; Chemical Ideas 11.1 page 244 figure 1 – Modern Day Periodic Table arranged by atomic number
Total number of words: 1006
Table Taken from Article 1 of Open Book Paper, Page5, Table 1
Table taken from http://home.earthlink.net/~ssbeaton/addlinfo/historypertable.html
Table taken from Salters Advanced Chemistry; Chemical Ideas 11.1 page 244 figure 1
Diagram taken from Salters Advanced Chemistry; Chemical Ideas 5.3 page 98 figure 18
Reactions taken from Article 1 of Open Book Paper page 6
Diagram taken from Article 1 of Open Book Paper, page 6 figure 6
Diagram taken from Article 1 of Open Book Paper, page 5 figure 3
Diagram taken from Article 2, figure 4 of Open Book Paper, page 2
