Periodicity of Valence or Oxidation States of Elements

Dhristi JEE 2022-24

Introduction to Periodicity of Valence States of Elements

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:

Element

Valency

Atomic Number

Hydrogen valency

1

1

Helium valency

0

2

Lithium valency

1

3

Beryllium valency

2

4

Boron valency

3

5

Carbon valency

4

6

Nitrogen valency

3

7

Oxygen valency

2

8

Fluorine valence

1

9

Neon valency

0

10

Sodium (Na) valency

1

11

Magnesium (Mg) valency

2

12

Aluminium valency

3

13

Silicon valency

4

14

Phosphorus valency

3

15

Sulphur valency

2

16

Chlorine valency

1

17

Argon valency

0

18

Potassium (K) valency

1

19

Calcium valency

2

20

Scandium valency

3

21

Titanium valency

4

22

Vanadium valency

5, 4

23

Chromium valency

2

24

Manganese valency

7, 4, 3

25

Iron (Fe) valency

2, 3

26

Cobalt valency

3, 2

27

Nickel valency

2

28

Copper (Cu) valency

2, 1

29

Zinc valency

1

30


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.


  1. 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.


  • 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.


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.

FAQs (Frequently Asked Questions)

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.

5. Define a method for determining the valency of items.

The valency of multi-element compounds can be calculated in a variety of methods. For example, to discover the valency of an element, such as phosphorus tetroxide, multiply the total valency of the four oxygen atoms (valency as 2) and then subtract it from the valency of the phosphorus atom (valency as 5) to get the solution of 3.You can read about the explained and in detail concepts of valency of elements with the free pdf of Periodicity of Valence or Oxidation States of Elements - Explanation. 

6. Why are there variable valencies in the elements?

The number of electrons that can be taken or donated is referred to as valency, and it is determined by the number of electrons present in the outer shell. As a result, each element has a different amount of electrons in its outermost shell, as well as a different electrical arrangement. Hence, the valency of the elements holds variable valency. Vedantu explains the concepts in a simpler manner with the help of a team of experts. Download the free pdf from Vedantu now. 

7. Differentiate valence and variable valency.

The combining capacity of an element is defined as valency. The valency of a metal is defined as the number of valence electrons it contains, whereas the valency of a non-metal is defined as 8 minus the number of valence electrons. However, the valency of the element can alter under certain circumstances. The variable valency refers to the valencies or altered valencies. The free document Periodicity of Valence or Oxidation States of Elements - Explanation explains valence and variable valency thoroughly.

8. Which components have more than one valency?

Multiple or variable valency exists in mercury, copper, and iron. Mercury has two valencies: 1 and 2, which are referred to as mercurous and mercuric, respectively. Iron also has valencies of 2 and 3, which are known as ferrous and ferric, respectively. Copper, on the other hand, has valencies of 1 and 2, which are known as cuprous and cupric, respectively. These elements contain multiple valanencies. You can study the concept of elements in an explained manner with the help of a free pdf of Periodicity of Valence or Oxidation States of Elements - Explanation.

9. Is the periodicity of valence or oxidation states of elements - Explanation helpful? 

The free PDF of Periodicity of Valence or Oxidation States of Elements - Explanation is very helpful. It provides the basic introduction of the concepts of periodicity of valence and oxidation states of elements. You’ll be able to know the theory behind the loss and gain of electrons and how it works. Vedantu provides the free online classes along with the pdf that provides help to students who aren’t clear about the concepts of periodicity. 

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