Gilbert N. Lewis was the one who postulated the octet rule.
The octet rule is a postulate used in the context of chemistry . Also known as the octet rule , this is the tendency of atoms to complete their energy level with eight electrons to achieve stability .
It should be noted that rule is a concept that has different meanings. In this case we are interested in highlighting its meaning as a precept or regulation . Octet , on the other hand, is something that is made up of eight components.
Origin of the octet rule
The American scientist Gilbert Newton Lewis was the one who, in 1917 , postulated the octet rule. Lewis warned that, by combining with each other, atoms try to achieve the structural electronic configuration that has the noble gas located closest on the periodic table of elements.
By looking at this table, you can see that noble gases have eight electrons in their last shell. The deduction led Lewis to affirm that this configuration is the most stable for any kind of atom .
The importance of Newton Lewis
Newton Lewis is a reference in the field of chemistry, who has also gone down in history for other works and discoveries. What stands out from his career is that he formulated the model of the cubic atom ; that he deduced the same relationship between mass and energy as Albert Einstein but that he arrived at it by another way; and to carry out the theory of the electronic pair , referring to what acid-base reactions are.
All this without overlooking that this North American biochemist - born in 1875 in Massachusetts and died in 1946 ) was responsible for coining the term photon in 1926 to refer to the smallest unit of radiant energy.
The octet rule recognizes the stability of noble gases.
Features of the octet rule
The octet rule, in short, indicates that two equal atoms, when bonded, develop a specific organization so that, when the bond is formed by the sharing of electron pairs, each atom acquires the structure of a noble gas . Thus, both atoms will be surrounded by eight electrons in their last energetic shell.
As with any rule, the octet rule also has exceptions . Oxygen , nitrogen and carbon are compounds that do not comply with the aforementioned rule since they are organized differently. In this way, when the links are formed, the trend of the octet rule is not recorded.
Carbon dioxide (CO2) obeys the octet rule.
Other exceptions
It should not be overlooked that three other elements are also considered exceptions to the octet rule:
- Aluminum (Al), which achieves stability with the existence of six electrons in the valence shell.
- Beryllium (Be), whose stabilization is found in four electrons, since it has the ability to form compounds with only two simple bonds.
- Boron (B), which forms substances with three simple bonds, hence it does not have to reach the eight set by the octet rule either.
Links and the octet rule
To comply with the octet rule, atoms are related in different ways, always taking into account electronegativity (the strength of an atom to attract electrons).
There are, in this framework, different types of links:
- Covalent bond (which can be a polar bond or a nonpolar bond )
- Metal link
- ionic bond
- Coordinated link
- Intermolecular bond
Each link has its particularities and, as we saw, exceptions that are linked to the octet rule. Covalent bonds, for example, involve a union between two non-metal atoms that share at least one valence electron; However, hydrogen does not meet this definition, since its stability is achieved with two electrons.
The Lewis model
It is interesting to note that the Lewis model , also referred to as the Lewis diagram or Lewis structure , is a structural formula that presents each pair of electrons with bond dots or dashes. This graphical representation, therefore, displays the chemical bonds that occur in a molecule and contributes to the understanding of the octet rule.
What the Lewis model allows is to know how many valence electrons of an element can interact between those of the same species or with others. Links are graphed with lines or pairs of points.
Octet Rule Examples
A common example given of the octet rule is carbon dioxide , whose molecules are made up of one carbon atom and two oxygen atoms.
The carbon atom is linked to the oxygen atoms by double covalent bonds . While the valence of the carbon atom is 4, the valence of the oxygen atoms is 2.
The octet rule states that each atom must have 8 electrons in its last energy level. For this, in the case of carbon dioxide, two electrons have to be shared : the carbon atom does so with each oxygen atom so that the last energy level of each of them reaches 8. In turn, each atom of oxygen does the same, ensuring that the electrons in the last energy level of carbon are also 8.
Another example of the octet rule can be seen in carbon monoxide , where oxygen contributes 4 electrons and carbon, 2: this results in a triple covalent bond, with a pair of free electrons on each atom to complete the octet.