Tabla de Contenidos
When combined with other elements, atoms can lose or gain electrons in order to acquire a more stable electronic configuration. When this happens, the atom that gains the electrons acquires a negative electrical charge, thus becoming an anion, while the one that loses them acquires a positive electrical charge, becoming a cation. In other words, by exchanging electrons and forming an ionic bond, atoms become ions .
In addition to exchanging electrons, atoms can also share them, thus forming a covalent bond. This bond can be polar if one of the two atoms attracts with greater force the electrons that form the bond, generating opposite partial electric charges in the two bonded atoms.
oxidation number
Even though many bonds are covalent and 100% ionic bonds don’t really exist, it’s convenient to think of all bonds as ionic bonds. This makes it easy to understand the number of links each element can form with other elements, and to calculate the proportions in which they combine. In this sense, whenever any compound is formed, whether ionic or not, it is usually characterized by the hypothetical electrical charge that each atom would have if the bond were 100% ionic and the electrons were completely transferred to the most electronegative atom. This hypothetical ionic charge is called the oxidation state or oxidation number.
Oxidation numbers or common ionic charges
Each element of the periodic table has a series of habitual oxidation numbers that it exhibits in the different compounds of which it is a part. These oxidation states determine many of the properties and characteristics of the compounds. In fact, there can be different compounds formed by the same elements and that differ only in the oxidation number of one of the elements. For example, ferric oxide (Fe 2 O 3 ), which contains iron in the +3 oxidation state, is a dark orange basic oxide, while ferrous oxide (FeO) is a dark, almost black solid. .
The oxidation number(s) common to each element depends on its position in the periodic table. Nonmetallic elements can exhibit both positive and negative oxidation states, whereas metals only exhibit positive oxidation states. In some cases, the same element can exhibit five or even six different oxidation states, depending on the element with which it is combined and the reaction conditions.
The periodic table at the beginning of the article shows the most common oxidation states for most of the known elements. As can be seen in it, the alkali metals all have a unique oxidation number, which is +1, the alkaline earths have +2 and the transition metals of group 3, as well as the representative elements of group 13 all have the state of oxidation +3. This is because positive oxidation states are usually related to the number of electrons an atom has in its valence shell, since losing these electrons allows it to acquire the electronic configuration of a noble gas.
On the other hand, among non-metals, the negative oxidation state can be easily determined by counting the number of cells to the right (not counting your own) that you still have to go to reach the group of noble gases. For example, carbon is four squares away from neon, so its negative oxidation state is -4. This is because this number represents the number of electrons the atom must gain to acquire the electron configuration of the nearest noble gas.
What is the periodic table of oxidation numbers used for?
This periodic table has two main applications:
Helps predict the formula of binary chemical compounds
The above table is very useful for predicting the different compounds that can be formed by combining two elements with each other. For example, knowing that the two most common oxidation states of nitrogen are +5 and -3, we can use this information to predict that by bonding with hydrogen (which is less electronegative), nitrogen will acquire the -3 oxidation state. while hydrogen will acquire +1, so a compound of formula NH 3 (ammonia) will be formed.
In contrast, if nitrogen binds to oxygen, which is more electronegative, it is likely to form an oxide with oxidation state +5 (N 2 O 5 ).
In traditional nomenclature
The traditional nomenclature system for inorganic compounds is based on a system of prefixes and suffixes that are added to the root of the name of the elements that make up a compound. The prefix-suffix system depends not only on the oxidation state of each element in the compound, but also on all the other common oxidation states it may exhibit in other compounds.
In this sense, the previous periodic table is very useful, since it allows us to determine, for most of the compounds, their traditional name from the oxidation state of each element in the compound, and from the other possible oxidation states that are found in the table.
Example:
In SO 3 , oxygen has an oxidation state of -2 (because it is more electronegative than sulfur), so sulfur must have an oxidation state of +6 to ensure the neutrality of the compound. This means that SO 3 is the acid oxide or anhydride of sulfur with oxidation state +6.
To name this compound according to the traditional system, we look for the common valences or oxidation states of sulfur (which are +2, +4 and +6). Because the +6 oxidation state is the highest of three possible oxidation states, traditional nomenclature rules dictate that the suffix “ico” be added to the root of sulfur’s name.
In conclusion, the name of the compound is sulfuric anhydride.
References
Alonso, C. (2021, May 11). Oxidation Number . Alonso Formula. https://www.alonsoformula.com/inorganica/numero_oxidacion.htm
Chang, R., & Goldsby, K. (2013). Chemistry (11th ed.). McGraw-Hill Interamericana de España SL
EcuRed. (n.d.). Valencia (Chemistry) – EcuRed . https://www.ecured.cu/Valencia_(Qu%C3%ADmica)
León, M., & Ceballos, M. (2012, October 21). Oxidation number (definition) . Maria Leon & Maria Ceballos. https://leonceballos.wordpress.com/2012/10/21/numero-de-oxidacion-definicion/
MIQ: States or oxidation numbers . (n.d.). MDP.EDU.AR. https://campus.mdp.edu.ar/agrarias/mod/page/view.php?id=4175
