[Chemistry Class Notes] on Periodicity of Valence or Oxidation States of Elements Pdf for Exam

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.”

What does Oxidation State Mean?

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. The valency of the element is a measure of its ability to combine with other elements and is defined as the number of electrons that an object must lose or receive in order to achieve a stable electron configuration.The number of electrons lost or acquired by an atom determines its oxidation state.

Oxidation is one of the most fundamental aspects of elements is state and valency, which may be explored using electron configurations.

Valency and Oxidation State

Generally, electrons that are found in the outermost shell are referred to as valence electrons. At the same time, the number of valence electrons defines 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.

Valence electrons are electrons that are present in the valence shell of a molecule, the outermost shell, and the quantity of valence electrons determines an atom’s valency (or valence).

• The number of valence electrons or eight subtracted from the number of valence electrons is used to compute the valencies of elements in the s-block and p-block of the periodic table.

• Valency is determined for the d-block and f-block elements not only by valence electrons but also by d and f orbital electrons. The typical valencies of these d and f block elements, on the other hand, are 2 and 3.

In the graphic below, the general oxidation state of the elements of the periodic table is depicted.

Valency of First 20 Elements

The periodic table’s valency of the first 30 elements can be tabulated as follows:

Periodic Trends in the Oxidation States of Elements

1. Changes in Oxidation Levels Over Time

The number of valence electrons of elements increases and ranges between 1 and 8 while travelling left to right over a period. However, when elements are mixed with H or O first, their valency increases from 1 to 4, then decreases to zero. Consider the following two oxygen-containing compounds: Na₂O and F₂O. F has a higher electronegativity than oxygen in F₂O.

2. Oxidation State Variation Within a Group

The number of valence electrons does not change as we travel down in a group. As a result, each group’s elements have the same valency.

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 zer
o. 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.

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.

Guidelines for assigning the Oxidation States

• Oxidation states of the elements such as S8, O₂, H₂, Fe, P₄, and more are 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

1. Halogens contain -1 except the time they produce a compound with Oxygen or one another.

2. Alkali Metals like K, Na, Rb, Cs, -Li; have +1

3. And, the Alkali Earth Metals holds +2 such as Ca, Mg, Ba, Sr, -Be, and more related.

Finding Valency of the Elements

As we probably already know, the element’s valency measures its ability to combine with the other elements. The number of electrons counted 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).

A System of Rules that governs the Assignment of Oxidation States

• The oxidation states of elements such as O₂, S₈, H₂, P₄, Fe, and others are all zero.

• The oxidation state of oxygen is -2. However, in peroxides such as Na₂O₂ and H₂O₂, it has an oxidation state of -1.

• Hydrogen, too, has a +1. However, it has a negative value in metal hydrides such as NaH, LiH, and others.

• Some elements, such as carbon, have the same oxidation states as their compounds.

• Except when they form a compound with one another or with Oxygen, halogens have a -1.

• Alkali metals, such as Na, K, Rb, Li, and Cs, have a positive charge.

• Mg, Ca, Ba, Be, Sr, and other alkali earth metals have a +2 rating.