The gallium It is a metallic element that is represented by the symbol Ga and that belongs to group 13 of the periodic table. Chemically it resembles aluminum in its amphotericism; However, both metals end up exhibiting properties that make them differentiable from each other..
For example, aluminum alloys can be worked to give them all kinds of shapes; while those of gallium have very low melting points, consisting practically of silvery liquids. Also, the melting point of gallium is lower than that of aluminum; the former can melt from the heat of the hand, while the latter cannot.
The chemical similarity between gallium and aluminum also groups them geochemically; that is, minerals or rocks rich in aluminum, such as bauxites, have estimable concentrations of gallium. Apart from this mineralogical source, there are others of zinc, lead and carbon, widely spread throughout the earth's crust..
Gallium is not popularly a well-known metal. Its mere name can conjure up the image of a rooster in the mind. In fact, graphic and general representations of gallium are usually found with the image of a silver rooster; painted with liquid gallium, a highly wettable substance on glass, ceramics and even the hand.
Experiments in which pieces of metallic gallium are melted with the hands are frequent, as well as the manipulation of its liquid and its tendency to stain everything it touches.
Although gallium is not toxic, as is mercury, it is a destroying agent of metals, as it makes them brittle and useless (in the first instance). On the other hand, pharmacologically it intervenes in the processes where biological matrices use iron.
For those in the world of optoelectronics and semiconductors, gallium will be held in high esteem, comparable and perhaps superior to silicon itself. On the other hand, with gallium thermometers, mirrors and objects based on its alloys have been manufactured.
Chemically, this metal still has a lot to offer; perhaps in the field of catalysis, nuclear energy, in the development of new semiconductor materials, or "simply" in the clarification of their confusing and complex structure.
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In 1871, the Russian chemist Dmitri Mendeleev had already predicted the existence of an element whose properties resembled those of aluminum; which, he named as ekaluminio. This element had to be located just below the aluminum. Mendeleev also predicted the properties (density, melting point, oxide formulas, etc.) of ekaluminium.
Surprisingly, four years later the French chemist Paul-Emili Lecoq de Boisbaudran, had found a new element in a sample of sphalerite (zinc blende), from the Pyrenees. He was able to discover it thanks to a spectroscopic analysis, in which he observed the spectrum of two violet lines that did not coincide with that of another element.
Having discovered a new element, Lecoq carried out experiments on 430 kg of sphalerite, from which he was able to isolate 0.65 grams of it; and after a series of measurements of its physical and chemical properties, he concluded that it was Mendeleev's ekaluminium.
To isolate it, Lecoq carried out the electrolysis of its respective hydroxide in potassium hydroxide; probably the same one with which he dissolved the sphalerite. By certifying that it was ekaluminium, and also being its discoverer, he gave it the name 'gallium' (galium in English). This name derived from the name 'Gallia', which in Latin means France.
However, the name presents another curiosity: 'Lecoq' in French means 'rooster', and in Latin 'gallus'. Being a metal, 'gallus' became 'gallium'; although in Spanish the conversion is much more direct. Thus, it is no coincidence that a rooster is thought of when talking about gallium..
Gallium is an odorless, glassy-surfaced silver metal with an astringent taste. Its solid is soft and brittle, and when it fractures it does so conchoidal; that is, the pieces formed are curved, similar to seashells.
When melted, depending on the angle at which it is viewed, it can show a bluish glow. This silvery liquid is not toxic on contact; however, it "clings" too much to surfaces, especially if they are ceramic or glass. For example, a single drop of gallium can permeate the inside of a glass cup to coat it with a silver mirror..
If a solid fragment of gallium is deposited in liquid gallium, it serves as a nucleus where glittering gallium crystals rapidly develop and grow..
31 (31Ga)
69.723 g / mol
29.7646 ° C. This temperature can be reached by holding a gallium glass tightly between both hands until it melts..
2400 ° C. Note the great gap between 29.7ºC and 2400ºC; that is, liquid gallium has a very low vapor pressure, and this fact makes it one of the elements with the greatest difference in temperature between the liquid and gaseous states..
-At room temperature: 5.91 g / cm3
-At melting point: 6.095 g / cm3
Note that the same thing happens with gallium as with water: the density of its liquid is greater than that of its solid. Therefore, your crystals will float on liquid gallium (gallium icebergs). In fact, the volume expansion of the solid is such (three times) that it is inconvenient to store liquid gallium in containers that are not made of plastics..
5.59 kJ / mol
256 kJ / mol
25.86 J / (mol K)
At 1037 ºC, only its liquid exerts a pressure of 1 Pa.
1.81 on the Pauling scale
-First: 578.8 kJ / mol (Ga+ gaseous)
-Second: 1979.3 kJ / mol (Gatwo+ gaseous)
-Third: 2963 kJ / mol (Ga3+ gaseous)
40.6 W / (m K)
270 nΩ · m at 20 ºC
1.5
1,819 cP at 32 ºC
709 dynes / cm at 30 ºC
Like aluminum, gallium is amphoteric; reacts with both acids and bases. For example, strong acids can dissolve it to form gallium (III) salts; if they are about the HtwoSW4 and HNO3, are produced Gatwo(SW4)3 and won3)3, respectively. While when reacting with strong bases, gallate salts are produced, with the ion Ga (OH)4-.
Note the similarity between Ga (OH)4- and Al (OH)4- (aluminate). If ammonia is added to the medium, gallium (III) hydroxide, Ga (OH) is formed3, which is also amphoteric; when reacting with strong bases, it produces Ga (OH) again4-, but if it reacts with strong acids it liberates the complex aqueous [Ga (OHtwo)6]3+.
Metallic gallium is relatively inert at room temperature. It does not react with air, as a thin layer of oxide, GatwoOR3, protects it from oxygen and sulfur. However, when heated the oxidation of the metal continues, completely transforming into its oxide. And if sulfur is present, at high temperatures it reacts to form GatwoS3.
There are not only gallium oxides and sulfides, but also phosphides (GaP), arsenides (GaAs), nitrides (GaN), and antimonides (GaSb). Such compounds can be originated by the direct reaction of the elements at elevated temperatures, or by alternative synthetic routes..
Likewise, gallium can react with halogens to form their respective halides; such as GatwoCl6, GaF3 and GatwoI3.
This metal, like aluminum and its congeners (members of the same group 13), can interact covalently with carbon atoms to produce organometallic compounds. In the case of those with Ga-C bonds, they are called organogaliums.
The most interesting thing about gallium is not any of its previous chemical characteristics, but its enormous ease with which it can be alloyed (similar to that of mercury and its amalgamation process). Its Ga atoms quickly “rub shoulders” between metallic crystals, resulting in gallium alloys..
Gallium is not only unusual in that it is a metal that melts with the heat of the palm of the hand, but its structure is complex and uncertain..
On the one hand, it is known that its crystals adopt an orthorhombic structure (Ga-I) under normal conditions; however, this is just one of the many possible phases for this metal, of which the exact order of its atoms has not been specified. It is therefore a more complex structure than it might appear at first glance..
It seems that the results vary according to the angle or direction in which its structure is analyzed (anisotropy). Likewise, these structures are very susceptible to the smallest change in temperature or pressure, which means that gallium cannot be defined as a single type of crystal at the time of data interpretation..
Ga atoms interact with each other thanks to the metallic bond. However, a certain degree of covalence has been found between two neighboring atoms, so the existence of the Ga dimer is assumed.two (Gaga).
In theory, this covalent bond should be formed by the overlap of the 4p orbital, with its only electron according to the electronic configuration:
[Ar] 3d10 4stwo 4p1
This mixture of covalent-metallic interactions is attributed the low melting point of gallium; since, although on the one hand there may be a "sea of electrons" that holds the Ga atoms tightly together in the crystal, on the other the structural units consist of Ga dimers.two, whose intermolecular interactions are weak.
When the pressure increases from 4 to 6 GPa, the gallium crystals undergo phase transitions; from the orthorhombic it passes to the body-centered cubic (Ga-II), and from this it finally passes to the body-centered tetragonal (Ga-III). In the pressure range, possibly a mixture of crystals is formed, which makes the interpretation of the structures even more difficult..
The most energetic electrons are those found in the 4s and 4p orbitals; as there are three of them, it is therefore expected that gallium may lose them when combined with elements more electronegative than it.
When this occurs, the existence of the Ga cation is assumed.3+, and its oxidation number or state is said to be +3 or Ga (III). In fact, this is the most common of all its oxidation numbers. The following compounds, for example, possess gallium as +3: GatwoOR3 (Gatwo3+OR3two-), GatwoBr6 (Gatwo3+Br6-), Li3GaNtwo (Li3+Ga3+Ntwo3-) and GatwoTea3 (Gatwo3+Tea3two-).
Gallium can also be found with oxidation numbers of +1 and +2; although they are much less common than +3 (similar as with aluminum). Examples of such compounds are GaCl (Ga+Cl-), GatwoO (Gatwo+ORtwo-) and GaS (Gatwo+Stwo-).
Note that the existence of ions with charge magnitudes identical to the oxidation number considered is always assumed (correctly or not)..
Gallium is found in the earth's crust with an abundance proportional to that of the metals cobalt, lead, and niobium. It appears as a hydrated sulphide or oxide, widely diffused as impurities contained in other minerals.
Its oxides and sulfides are poorly soluble in water, so the concentration of gallium in seas and rivers is low. Furthermore, the only mineral “rich” in gallium is gallita (CuGaStwo, picture above). However, it is impractical to exploit the chicken to obtain this metal. Less well known is the mineral gallium plumbogumite.
Therefore, there are no ideal ores for this metal (with a concentration greater than 0.1% by mass)..
Instead, gallium is obtained as a by-product of metallurgical treatment of ores of other metals. For example, it can be extracted from bauxites, zinc blenders, alums, coals, galenas, pyrites, germanites, etc .; that is, it is usually associated with aluminum, zinc, carbon, lead, iron and germanium in different mineral bodies.
When the mineral raw material is digested or dissolved, either in strongly acidic or basic media, a mixture of metal ions solubilized in water is obtained. As gallium is a by-product, its Ga ions3+ remain dissolved in the mixture once the metals of interest have precipitated.
Thus, you want to separate these Ga3+ of the other ions, with the sole purpose of increasing their concentration and the purity of the resulting metal.
For this, in addition to conventional precipitation techniques, ion exchange chromatography is used using a resin. Thanks to this technique it is possible to separate (for example) the Ga3+ of Catwo+ o Faith3+.
Once a highly concentrated solution of Ga ions has been obtained3+, it is subjected to electrolysis; that is, the Ga3+ receives electrons to be able to form as a metal.
Gallium is found in nature mainly as two isotopes: the 69Ga, with an abundance of 60.11%; and the 71Ga, with an abundance of 39.89%. It is for this reason that the atomic weight of gallium is 69.723 u. The other isotopes of gallium are synthetic and radioactive, with atomic masses ranging from 56Ga a 86Ga.
From an environmental point of view, metallic gallium is not very reactive and soluble in water, so its spills in theory do not represent severe contamination risks. In addition, it is unknown what biological role it may have in organisms, with most of its atoms being excreted in the urine, with no signs of accumulating in any of its tissues..
Unlike mercury, gallium can be handled with bare hands. In fact, the experiment of trying to melt it with the heat of the hands is quite common. A person can touch the resulting silver liquid without fear of damaging or injuring their skin; though it does leave a silver stain on it.
However, ingesting it could be toxic, since in theory it would dissolve in the stomach to generate GaCl3; gallium salt whose effects on the body are independent of the metal.
Gallium is characterized by highly staining or adhering to surfaces; and if these are metallic, it goes through them and forms alloys instantly. This characteristic of being able to be alloyed with almost all metals makes it inappropriate to spill liquid gallium on any metal object..
Therefore, metallic objects run the risk of shattering into pieces in the presence of gallium. Its action can be so slow and unnoticed that it brings undesirable surprises; especially if it has been spilled on a metal chair, which could collapse when someone sits on it.
That is why those who wish to handle gallium should never put it in contact with other metals. For example, its liquid is capable of dissolving aluminum foil, as well as sneaking into indium, iron and tin crystals, to make them brittle..
In general terms, despite the aforementioned, and the fact that its vapors are almost absent at room temperature, gallium is usually considered a safe element with zero toxicity..
Gallium has replaced mercury as the liquid to read the temperatures marked by the thermometer. However, its melting point of 29.7 ºC is still high for this application, which is why in its metallic state it would not be feasible to use it in thermometers; instead, an alloy called Galinstan (Ga-In-Sn) is used.
Galinstan alloy has a melting point around -18 ºC, and added its zero toxicity makes it an ideal substance for the design of mercury-independent medical thermometers. This way, if it were to break it would be safe to clean up the mess; although it would dirty the floor due to its ability to wet surfaces.
Again, mention is made of the wettability of gallium and its alloys. When touching a porcelain surface, or glass, it spreads over the entire surface until it is completely covered in a silver mirror.
In addition to mirrors, gallium alloys have been used to create objects of all shapes, since once they cool they solidify. This could have great nanotechnological potential: to build objects of very small dimensions, which would logically operate at low temperatures, and would show unique properties based on gallium..
Thermal pastes used in computer processors have been made from gallium alloys.
Ga ions3+ bear a certain resemblance to the Fe3+ in the way in which they intervene in metabolic processes. Therefore, if there is a function, parasite or bacteria that require iron to perform, they can be stopped by mistaking it for gallium; such is the case of pseudomonas bacteria.
So, this is where gallium drugs appear, which may simply consist of its inorganic salts, or organogaliums. La Ganita, trade name for gallium nitrate, Ga (NO3)3, used to regulate the high calcium levels (hypercalcaemia) associated with bone cancer.
Gallium arsenide and nitride are characterized by being semiconductors, which have come to replace silicon in certain optoelectronic applications. With them, transistors, laser diodes and light emitting diodes (blue and violet), chips, solar cells, etc. have been manufactured. For example, thanks to GaN lasers, Blu-Ray discs can be read.
Gallium oxides have been used to study their catalysis in different organic reactions of great industrial interest. One of the newer gallium catalysts consists of its own liquid, over which atoms of other metals are dispersed that function as the active centers or sites..
For example, the gallium-palladium catalyst has been studied in the dehydrogenation reaction of butane; that is, to convert butane into more reactive unsaturated species, necessary for other industrial processes. This catalyst consists of liquid gallium acting as a support for the palladium atoms..
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