The silver oxide is an inorganic compound whose chemical formula is AgtwoO. The force that binds its atoms is entirely ionic in nature; therefore, it consists of an ionic solid where there is a proportion of two cations Ag+ interacting electrostatically with an anion Otwo-.
The oxide anion, Otwo-, It results from the interaction of the silver atoms on the surface with the oxygen in the environment. in much the same way as iron and many other metals do. Instead of reddening and crumbling into rust, a piece or jewel of silver turns black, characteristic of silver oxide..
For example, in the image above you can see an oxidized silver cup. Note its blackened surface, although it still retains some ornamental luster; which is why even oxidized silver objects can be considered attractive enough for decorative uses.
The properties of silver oxide are such that they do not, at first glance, eat away at the original metal surface. It is formed at room temperature by simple contact with oxygen in the air; and even more interesting, it can decompose at high temperatures (above 200 ° C).
This means that if the glass in the picture were grasped, and the heat of an intense flame were applied to it, it would regain its silver glows. Therefore, its formation is a thermodynamically reversible process..
Silver oxide also has other properties and, beyond its simple formula AgtwoOr, it encompasses complex structural organizations and a rich variety of solids. However, the AgtwoOr is it perhaps, next to the AgtwoOR3, the most representative of silver oxides.
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How is its structure? As mentioned at the beginning: it is an ionic solid. For this reason, there can be neither Ag - O nor Ag = O covalent bonds in its structure; since, if there were any, the properties of this oxide would change drastically. It is then Ag ions+ metwo- in a 2: 1 ratio and experiencing electrostatic attraction.
The structure of silver oxide is consequently determined by the way in which ionic forces arrange the Ag ions in space.+ metwo-.
In the image above, for example, there is a unit cell for a cubic crystal system: the cations Ag+ are the silver-blue spheres, and the Otwo- the reddish spheres.
If the number of spheres is counted, it will be found that there are, with the naked eye, nine silvery blue and four red. However, only the fragments of the spheres contained within the cube are considered; counting these, being fractions of the total spheres, the proportion 2: 1 for the AgtwoOR.
Repeating the structural unit of the AgO tetrahedron4 surrounded by four other Ag+, the entire black solid is built (avoiding the gaps or irregularities that these crystalline arrangements may have).
Focusing now not on the AgO tetrahedron4 but in the AgOAg line (observe the vertices of the upper cube), it will be seen that the silver oxide solid consists, from another perspective, of multiple layers of ions arranged linearly (although inclined). All this as a result of the "molecular" geometry around Ag+.
This has been corroborated by several studies of its ionic structure..
Silver works predominantly with valence +1, since when losing an electron its resulting electronic configuration is [Kr] 4d10, which is very stable. Other valences, such as Agtwo+ and Ag3+ they are less stable as they lose electrons from nearly full d orbitals.
The Ag ion3+, however, it is relatively less unstable compared to Agtwo+. In fact, it can coexist in the company of Ag+ chemically enriching the structure.
Its electron configuration is [Kr] 4d8, with unpaired electrons in such a way that it gives it some stability.
Unlike linear geometries around Ag ions+, it has been found that that of Ag ions3+ it is square plane. Hence, a silver oxide with Ag ions3+ would consist of layers composed of squares of AgO4 (not tetrahedra) electrostatically linked by AgOAg lines; such is the case of Ag4OR4 or AgtwoO ∙ AgtwoOR3 with monoclinic structure.
Scraping the surface of the silver cup in the main image would result in a solid, which is not only black in color, but also has shades of brown or brown (top image). Some of its physical and chemical properties reported at the moment are the following:
231.735 g / mol
Black-brown solid in powder form (note that despite being an ionic solid, it lacks a crystalline appearance). It is odorless and mixed with water gives it a metallic taste
7.14 g / mL.
277-300 ° C. Certainly it melts into solid silver; that is, it probably decomposes before forming the liquid oxide.
1.52 ∙ 10-8 in water at 20 ° C. It is therefore a compound hardly soluble in water.
If you look closely at the image of its structure you will find that the spheres of Agtwo+ metwo- they do not differ almost in size. This results in that only small molecules can pass through the interior of the crystalline lattice, making it insoluble in almost all solvents; except for those where it reacts, such as bases and acids.
Although silver oxide has been repeatedly said to be an ionic compound, certain properties, such as its low melting point, contradict this claim..
Certainly, the consideration of the covalent character does not destroy what has been explained for its structure, since it would be enough to add in the structure of AgtwoOr a model of spheres and bars to indicate covalent bonds.
Likewise, the tetrahedra and square planes AgO4, as well as AgOAg lines, they would be linked by covalent bonds (or ionic covalent).
With this in mind, the AgtwoOr it would actually be a polymer. However, it is recommended to consider it as an ionic solid with covalent character (whose nature of the bond is still a challenge today).
At first it was mentioned that its formation is thermodynamically reversible, so it absorbs heat to return to its metallic state. All of this can be expressed by two chemical equations for such reactions:
4Ag (s) + Otwo(g) => 2AgtwoO (s) + Q
2AgtwoO (s) + Q => 4Ag (s) + Otwo(g)
Where Q represents heat in the equation. This explains why the fire burning the surface of the oxidized silver cup returns it to its silvery glow..
Therefore, it is difficult to assume that there is AgtwoO (l) since it would decompose instantly from the heat; Unless the pressure is raised too high to get said brown black liquid.
When the possibility of Ag ions was introducedtwo+ and Ag3+ in addition to the common and predominant Ag+, the term 'silver oxide' begins to seem insufficient to refer to AgtwoOR.
This is because the Ag ion+ is more abundant than the others, so the Ag is takentwoOr as the only oxide; which is not correct at all.
If Agtwo+ as it is practically non-existent given its instability, we will then have only the ions with valences +1 and +3; i.e. Ag (I) and Ag (III).
Since Ag (I) is the one with the lowest valence, it is named by adding the suffix -oso to its name argentum. Thus the AgtwoEither it is: silver oxide or, according to the systematic nomenclature, diplate monoxide.
If Ag (III) is completely ignored, then its traditional nomenclature should be: silver oxide instead of silver oxide.
On the other hand, Ag (III) being the highest valence, the suffix -ico is added to its name. Thus the AgtwoOR3 is: silver oxide (2 Ag ions3+ with three O'stwo-). Also, its name according to the systematic nomenclature would be: diplata trioxide.
If the structure of AgtwoOR3, it can be presumed that it is the product of oxidation by ozone, OR3, instead of oxygen. Therefore, its covalent character must be greater as it is a covalent compound with Ag-O-O-O-Ag or Ag-O bonds.3-Ag.
The AgO, also written as Ag4OR4 or AgtwoO ∙ AgtwoOR3, It is an oxide of silver (I, III), since it has both +1 and +3 valences. Its name according to the systematic nomenclature would be: tetra silver tetraoxide.
This nomenclature is of great help when it comes to other, more stoichiometrically complex oxides of silver. For example, suppose the two solids 2AgtwoO ∙ AgtwoOR3 and AgtwoO ∙ 3AgtwoOR3.
Writing the first one more appropriately would be: Ag6OR5 (counting and adding the atoms of Ag and O). Its name would then be hexaplate pentoxide. Note that this oxide has a less rich silver composition than AgtwoOr (6: 5 < 2:1).
While writing the second solid in another way, it would be: Ag8OR10. Its name would be octa-silver decaoxide (with an 8:10 or 4: 5 ratio). This hypothetical silver oxide would be "very oxidized".
Studies in search of new and sophisticated uses for silver oxide continue to this day. Some of its uses are listed below:
-It dissolves in ammonia, ammonium nitrate, and water to form the Tollens reagent. This reagent is a useful tool in qualitative analysis within organic chemistry laboratories. It allows determining the presence of aldehydes in a sample, with the formation of a "silver mirror" in the test tube as a positive response..
-Together with metallic zinc, it forms the primary zinc-silver oxide batteries. This is perhaps one of its most common and home uses.
-It serves as a gas purifier, absorbing for example COtwo. When heated, it releases trapped gases and can be reused multiple times.
-Due to the antimicrobial properties of silver, its oxide is useful in bioanalysis and soil purification studies..
-It is a mild oxidizing agent capable of oxidizing aldehydes to carboxylic acids. It is also used in the Hofmann reaction (of tertiary amines) and participates in other organic reactions, either as a reagent or a catalyst..
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