The valencia cape It is one whose electrons are responsible for the chemical properties of an element. The electrons in this shell interact with those of a neighboring atom, thus forming covalent bonds (A-B); and if they migrate from one atom to another more electronegative, ionic bonds (A + B-).
This layer is defined by the principal quantum number n, which in turn indicates the period where the element is found in the periodic table. While the group ordering depends on the number of electrons orbiting in the valence shell. So for a n equal to 2, it can occupy eight electrons: eight groups (1-8).
The image above illustrates the meaning of the valence layer. The black point in the center of the atom is the nucleus, while the remaining concentric circles are the electronic shells defined by n.
How many layers does this atom have? Each of them has its own color, and since there are four, then the atom has four layers (n= 4). Note also that the color degrades as the distance from the layer to the core increases. The valence layer is the one that is furthest from the nucleus: the one with the lightest color.
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According to the image, the valence shell is nothing more than the last orbitals of an atom occupied by electrons. In the light blue cape, to n= 4, there are a series of 4s, 4p, 4d and 4f orbitals; that is, inside there are other sublayers with different electronic capabilities.
An atom needs electrons to fill all the 4n orbitals. This process can be observed in the electronic configurations of the elements over a period.
For example, potassium has an [Ar] 4s electron configuration1, while calcium, to its right, [Ar] 4stwo. According to these settings, what is the valence layer? The term [Ar] refers to the electronic configuration of the noble gas argon 1stwo2stwo2 P63stwo3p6. This represents the inner or closed layer (also known as kernel).
Since the 4s orbital is the one with the highest energy, and in which the new electrons enter, it represents the valence shell for both K and Ca. If the K and Ca atoms were compared with the one in the image, [Ar] would be all the inner layers colored blue; and 4s the light blue layer, the outer.
From all the above said, some characteristics of the valence shell for all atoms can be summarized:
-Your energy level is higher; what is the same, it is further removed from the nucleus and has the lowest electron density (compared to other layers).
-It's incomplete. Therefore, it will continue to fill up with electrons as a period is traversed from left to right in the periodic table..
-Intervenes in the formation of covalent or ionic bonds.
In the case of the metals potassium and calcium, they are oxidized to become cations. The K+ has electronic configuration [Ar], because it loses its only external electron 4s1. And on the side of Catwo+, its configuration is also [Ar]; because instead of losing one electron, you lose two (4stwo).
But what is the difference between the K+ and the Catwo+, if they both lose their valence shell electrons and have [Ar] electron configuration? The difference is in their ionic radii. ACtwo+ is smaller than K+, because the calcium atom has an additional proton that attracts external electrons with greater force (closed or valence shells).
The valence layer 4s has not disappeared: it is only empty for these ions.
The concept of the valence shell can be found directly or indirectly in many aspects of chemistry. Since its electrons are those that participate in the formation of bonds, any topic that addresses them (TEV, RPECV, reaction mechanisms, etc.) should refer to said layer.
This is because, more important than the valence shell, are its electrons; called valence electrons. When represented in the progressive construction of electronic configurations, these define the electronic structure of the atom, and therefore its chemical properties..
From this information of an A and a B atom, the structures of their compounds can be outlined through the Lewis structures. Likewise, the electronic and molecular structures of a range of compounds can be determined thanks to the number of valence electrons..
The simplest possible examples of valence layers are found in the periodic table; specifically, in electron configurations.
It is possible to identify an element and its location in the periodic table only with the electron configuration. Thus, if an element X has configuration [Kr] 5stwo5 p1, What is it and to what period and group does it belong?
Given the n= 5, X is in the fifth period. In addition, it has three valence electrons: two in the 5s orbitaltwo and one in the 5p1. The inner layer [Kr] does not provide more information.
Since X has three electrons, and its 5p orbitals are incomplete, it is in the p block; moreover, in group IIIA (Romanesque system) or 13 (current numbering system approved by the IUPAC). X is then the element Indian, In.
What is the element X with electron configuration [Kr] 4d105s1? Note that like In, it belongs to period 5, since the 5s orbital1 it is the one with the highest energy. However, the valence shell also includes the 4d orbitals, since they are incomplete.
The valence layers can then be designated as nsnp, for an element of the p or s block; or (n-1) dns, for an element of block d. So the mysterious element X belongs to block d because its electronic configuration is of the type (n-1) dns (4d105s1).
Which group do you belong to? Adding the ten electrons of the 4d orbital10, and one from 5s1, X has eleven valence electrons. Therefore, it must be located in group IB or 11. Moving then through period 5 of the periodic table to group 11, you stumble upon the element silver, Ag.
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