Definition of the Octet Rule

If we look at the last group of the Periodic table, which groups the gases noble, we see that they have the last complete level with eight valence electrons, which gives them some stability and the ability to behave as inert gases, since they do not react chemically with other chemical species... why? Because they do not tend to gain or lose valence electrons. This allowed to explain the behavior of the other elements of the Periodic Table, which gain, lose or share electrons in After being chemically stabilized, achieving the nearest noble gas electron configuration, completing eight valence electrons.

Like everything in nature, there are exceptions to the Rule. There are elements that achieve a certain stability and a lower state of

Energy with more or less than eight electrons at its last level. Starting with the first element in the periodic table, Hydrogen (H), which is stabilized with two electrons since it has a single atomic orbital. Other cases are: Beryllium (Be), Boron (Bo) who stabilize with four and six electrons, respectively, or Sulfur (S) who can stabilize with eight, ten or twelve valence electrons due to the possibility of adding a "d" orbital in its configuration electronics. We can also mention Helium (He), Phosphorus (P), Selenium (Se) and Silicon (Si). Note that Helium (He) is the only noble gas with only two valence electrons.

Examples of the octet rule in ionic, covalent, and metallic bonding

As an atom loses, gains or shares electrons, different bonds are formed that give rise to new compounds. In general, we can group these bonds into three major variants: ionic bond, covalent or metallic bond.

When an element loses or gains electrons to stabilize itself, completely transferring its valence electrons it is called ionic bonding, while if electrons are shared by the species in play it is called bond covalent. Finally, if the elements that are in play are metals whose cations are united immersed in a sea of ​​electrons, the bond will be metallic. Each of these types of unions have particular characteristics, however, they share a characteristic in In common, the interaction of electrons occurs in search of stability and the lowest energy to fulfill the Rule of Octet.

Let's look at each of the joints in more detail. In the case of covalent bonding, it is given by the possibility of sharing electrons, this generally happens between non-metallic elements such as, for example: Cl2 (Molecular Chlorine) or CO2 (Carbon Dioxide) and even H2O (Water). The intermolecular forces that govern these junctions will be reason from another section.

The case of metallic unions, we mention that it occurs between metals such is the case of Copper (Cu), Aluminum (Al) or Tin (Sn). As metals tend to donate their electrons to stabilize themselves, they will form charged species called cations (with positive charges), these ions immersed in a large electron cloud form compounds metallic. Electrons can be freely scattered within that structure. The forces that hold them together are metallic forces that give it certain characteristics such as high conductivity.

The ionic bond is characterized by having forces of attraction between the very intense elements that form it, called electrostatic forces and this is so because, as we saw, there is a gain and a net transfer of electrons between the elements forming charged species, ions. In general, they are unions formed by a metallic and a non-metallic element, whose electronegativity difference is so great that it allows the donation of valence electrons. Typically the you go out They are ionic compounds such as: NaCl (Sodium Chloride, table salt) and LiBr (Lithium Bromide).

The existence of these three bonds is explained as a transition in terms of the electronegativity of the compounds that form it. When the electronegativity difference is very large, the elements tend to form ionic bonds while, if the Elements possessing similar electronegativities will tend to share bonding electrons and will be type bonds covalent. When there is no electronegativity difference between the elements (for example, Br2) the bond will be nonpolar covalent while that, as the electronegativity difference increases, the covalent bond becomes further polarized, going from weak to strong.

Bibliography

• Notes from the chair, General Chemistry I, UNMdP, Faculty of engineering, 2019.

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