The valency of an element is described as a measure of its combining capacity, and it can be defined as "the number of electrons that should be gained or lost by an atom to obtain the stable electron configuration."
The oxidation state of an atom is defined as the number of electrons gained or lost by it.
Valency and Oxidation State are the most fundamental properties of the elements and are studied with the electron configurations' help.
Generally, electrons that are found in the outermost shell are referred to as valence electrons. At the same time, the number of valence electrons defined the valency or valence of an atom.
In general, the elements' valencies belonging to both the s-block and the p-block of the periodic table are calculated as eight minus the number of valence electrons or the number of valence electrons.
For the d and f-block elements, valency can be determined not only based on the valence electrons but also on both d and f orbital electrons. However, these d and f block elements' general valencies are given as 2 and 3.
The general oxidation state of the elements present in the periodic table can be illustrated in the chart provided below.
(Image to be added soon)
The periodic table’s valency of the first 30 elements can be tabulated as follows:
Variation of Oxidation State Along a Period
While moving from left to right across a period, the elements' number of valence electrons increases and changes between 1 to 8. Whereas the valency of the elements, when first combined with H or O, increases from 1 to 4, and after that, it reduces to zero. Let us consider two compounds with oxygen Na2O and F2O. In the F2O compound, the electronegativity of F is more than that of oxygen.
Thus, each of the F atoms will attract one electron from the oxygen compound. It means F will exhibit a -1 oxidation state, and O will exhibit a +2 oxidation state. On the other side, in the case of Na2O, oxygen is highly electronegative compared to a sodium atom. Therefore, oxygen will attract 2 electrons from each of the sodium atoms exhibiting a -2 oxidation state, and the Na compound will hold the oxidation state of +1.
The element's oxidation state represents the charge possessed by an atom because of the gain or loss of electrons (because of the electronegativity difference that exists between the combining atoms) in the molecule.
Variation of Oxidation State within a Group
While we move down in a group, there occurs no change in the number of valence electrons. Thus, all the elements of one group hold the same valency.
Oxidation states of the elements such as S8, O2, H2, Fe, P4, and more related is zero.
Oxygen contains a -2 oxidation state. Whereas, in its peroxides such as H2O2 and Na2O2, it contains an oxidation state of -1.
In the same way, hydrogen contains +1. But coming to the Metal Hydrides, like LiH, NaH, and more related, it has -1
Also, a few elements contain similar oxidation states as in their compounds like
Halogens contain -1 except the time they produce a compound with Oxygen or one another.
Alkali Metals like K, Na, Rb, Cs, -Li; have +1
And, the Alkali Earth Metals holds +2 such as Ca, Mg, Ba, Sr, -Be, and more related.
As we probably already know, the element's valency measures its ability to combine with the other elements. The number of electrons counts within the outer shell of the element determines its valency. There are several methods to calculate the element's valency (otherwise molecule, for that matter).
Let us look at one of the methods of finding the valency of the elements.
The first and the easiest method is simply to consult the periodic table: the elements are sorted into the groups, and the elements present in the groups (1–8 respectively) contain similar valency the same as others in their group. For suppose, all the elements in group 8 contain 8 electrons (with high stability).
1. Describe a method to find the valency of the elements?
We can calculate the valency of the multi-element molecules in many ways. For suppose, to determine the valency of an element, let us say, phosphorus tetroxide, we would multiply the total valency of the 4 oxygen atoms (valency as 2) and then subtract that from the valency of the phosphorus atom (valency as 5) to find the solution of 3.
2. Why do the elements contain variable valencies?
The term valency can be described as the number of electrons that can be accepted or donated, and it depends on the number of electrons present in the outer shell.
Therefore, every element contains a variable number of electrons in its outermost shell and variable electronic configuration. Hence, the valency of the elements holds variable valency.
3. Differentiate valence and variable valency?
Valency is explained as the combining capacity of an element. For metal, we can say that its valency is described as the number of valence electrons it contains, whereas, for non-metal, it is: 8 minus the number of valence electrons.
But at times, under some special conditions, the valency of the element changes. The valencies or changed valencies are referred to as the variable valency.
4. Which elements contain multiple valencies?
MERCURY, COPPER, and IRON contain multiple or variable valency. Mercury holds a valency of 1 and 2, called mercurous and mercuric, respectively. And, iron contains a valency of 2 and 3, called ferrous and ferric, respectively. In contrast, copper holds a valency of 1 and 2, called cuprous and cupric, respectively.