A anion It is any chemical species with a negative charge, in addition to being one of the two types of existing ions. Its negative charge originates from the fact that it has an excess of electrons compared to the neutral form of the species; for each additional electron, its negative charge increases by one unit.
The negative charge can be located on one or more atoms, as well as include its influence on a molecule as a whole. For simplicity, regardless of where the charge is (-), the entire species, compound, or molecule is considered an anion..
If a neutral species X gains an electron, the excess of negative charges will manifest itself in the formation of the anion X-, which will also lead to an increase in its atomic radius (upper image, with green spheres). X and X- differ enormously in their properties and in the way they interact with their environment.
If X is now assumed to be the H atom, for example, a cation or anion can arise from it: H+ or H-, respectively. The cation H+ It is the hydrogen ion, also called a proton; and the H- is the hydride anion, the "simplest" of all known anions.
Article index
The formation of an anion can easily be explained within theory; Although, experimentally, it can become a challenge, especially if you want it pure, without positive charges attracted by its negative charges..
An anion will form when there is an excess or gain of electrons in an atom. Said gain can be determined by making use of the formal charges in a Lewis structure. Also, using the previous method, you can know exactly which atom or group of them the negative charge comes from..
When atoms form covalent bonds, even if the distribution of electrons is equal, there may be a partial loss of electrons. In this sense, the fewer bonds the more electronegative atoms form, the more free pairs of electrons they will have and therefore exhibit negative charges..
Consider for example the molecule of ammonia, NH3. NH3 it is neutral and therefore has no electrical charges. If an H were removed, that is, an N-H bond was broken, the anion NH would be obtainedtwo-. Drawing its Lewis structure and calculating the formal charge of N, this can be verified.
Following the breaking of more N-H bonds, we now have the NH aniontwo-; and eliminating the last H, the anion N is finally obtained3-, called nitride anion. Nitrogen no longer has a way to gain more electrons, and its -3 charge is the most negative it can reach; their orbitals do not give for more.
An anion can be formed as a result of a reduction: it gains electrons by oxidizing another species, which loses them. Oxygen, for example, represents this type of chemical reaction very well..
When oxygen is reduced, it oxidizes to another species, and becomes the oxide anion, Otwo-; present in countless minerals and inorganic compounds.
An atom can gain electrons if it is in the gas phase:
X (g) + e- => X-(g)
This way of forming an anion implies a wide knowledge of physical techniques, while gaseous anions are not easy to study, nor are all species easily volatilized or atomized to the gaseous phase..
In general terms, the typical characteristics of an anion will be mentioned below before discussing their types and examples:
-It is more voluminous than the neutral atom from which it is derived.
-It can be more or less stable, despite the increasing electronic repulsion between its own electrons.
-If the anion comes from a low electronegative atom, such as carbon, it is very reactive.
-Establish strong dipole moments.
-Further increases its interaction with polar solvents.
-The monatomic anion is isoelectronic to the noble gas of its period; that is, it has the same number of electrons in its valence shell.
-It can polarize the electron cloud of a neighboring atom, repelling its outer electrons.
As its name suggests, it is an anion consisting of a single atom: the negative charge is well localized. Each group in the periodic table has characteristic negative charges; and since they are anions, they are the nonmetals located in the p block. Some examples and their names are below:
-Cl-, chloride.
-I-, I last.
-F-, fluoride.
-Br-, bromide.
-ORtwo-, oxide.
-Stwo-, sulfide.
-I knowtwo-, selenide.
-Teatwo-, telluride.
-Potwo-, poloniur.
-N3-, nitride.
-P3-, phosphide.
-Ace3-, arsenide.
-Sb3-, antimonurus.
-C4-, carbide.
-Yes4-, silicide.
-B3-, boruro.
Oxoanions are characterized by having an X = O bond, where X can be any non-metallic element (except fluorine), or a metal (chromium, manganese, ect.). They can also have one or more X-O simple links.
Some oxoanions with their respective names are:
-ClO-, hypochlorite.
-BrO-, hypobromite.
-IO-, hypoiodite.
-ClOtwo-, chlorite.
-ClO3-, chlorate.
-IO3-, iodate.
-ClO4-, perchlorate.
-PO43-, phosphate.
-CO3two-, carbonate.
-CrO4two-, chromate.
-CrtwoOR7two-, dichromate.
-SW4two-, sulfate.
-StwoOR3two-, thiosulfate.
-NOT3-, nitrate.
-NOTtwo-, nitrite.
-BO33-, borate.
-AsO43-, arsenate.
-PO33-, phosphite.
-MnO4-, permanganate.
Organic molecules have functional groups that can become electrically charged. How? Through the formation or breaking of covalent bonds, very similar to the example of the NH molecule3.
Some organic anions are:
-CH3COO-, acetate.
-HCOO-, Format.
-CtwoOR4two-, oxalate.
-RCOO-, carboxylate.
-CH3CONH-, amidate.
-RO-, alkoxide.
-R3C-, carbanion.
-CH3OR-, methoxide.
Oxoanions are also polyatomic anions, that is, they consist of more than one atom. The same happens with organic anions. However, polyatomics do not fall into any of the above classifications. Some of them are:
-CN-, cyanide (has a triple bond, C≡N).
-OCN-, cyanate.
-SCN-, thiocyanate.
-NHtwo-, Amide.
-Oh-, hydroxyl, hydroxide or hydroxyl.
-ORtwo-, superoxide.
-ORtwotwo-, peroxide.
In organic anions some negatively charged functional groups were mentioned. These groups can be part of a large molecule, and thus the anion can be a whole robust compound with many bonds. The simplest of this type of anions is the hypothetical molecule of Htwo-.
Another example of these anions are polysulfides, Sntwo-, which consist of chains with multiple S-S bonds. Also, negatively charged metal coordination compounds such as [CoCl4(NH3)two]- and [CuCl4]two-.
Yet No Comments