Oxidation Number vs. Valency

Attribute	Oxidation Number	Valency
Definition	The hypothetical charge assigned to an atom in a compound or ion	The combining capacity of an atom in a compound
Representation	Written as a positive or negative integer	Written as a positive integer
Significance	Indicates the electron transfer in a chemical reaction	Indicates the number of bonds an atom can form
Can be fractional?	Yes	No
Can be zero?	Yes	No
Can be different for different compounds?	Yes	Yes
Can be different for different atoms in the same compound?	Yes	Yes
Can change during a reaction?	Yes	No

Introduction

Oxidation number and valency are two important concepts in chemistry that help us understand the behavior of elements and compounds. While they both relate to the electron configuration of atoms, they have distinct characteristics and applications. In this article, we will explore the attributes of oxidation number and valency, highlighting their similarities and differences.

Oxidation Number

Oxidation number, also known as oxidation state, is a concept used to describe the degree of oxidation or reduction of an atom in a compound. It is a hypothetical charge assigned to an atom, assuming that all the shared electrons are assigned to the more electronegative atom in a bond. Oxidation numbers can be positive, negative, or zero, depending on the electron transfer in a chemical reaction.

One of the key attributes of oxidation numbers is that they can be fractional or decimal values, representing partial electron transfers. For example, in the compound H2O2 (hydrogen peroxide), each oxygen atom has an oxidation number of -1, while the overall molecule is neutral. This fractional oxidation number indicates that the oxygen atoms have not fully gained or lost electrons.

Oxidation numbers are essential in balancing redox reactions, where electrons are transferred between species. By assigning oxidation numbers to each atom, we can determine the changes in oxidation states and balance the equation accordingly. Additionally, oxidation numbers help in identifying the oxidizing and reducing agents in a reaction.

It is important to note that oxidation numbers are not necessarily related to the actual charge of an atom in a compound. For example, in the compound NaCl (sodium chloride), the oxidation number of sodium is +1, while the actual charge of the sodium ion is +1. However, in some cases, the oxidation number and the charge may coincide, such as in simple ionic compounds.

Valency

Valency, on the other hand, is a concept used to describe the combining capacity of an atom or ion. It represents the number of electrons an atom can gain, lose, or share to achieve a stable electron configuration. Valency is typically associated with the outermost energy level (valence shell) of an atom.

Unlike oxidation numbers, valency is always a whole number. It is determined by the number of valence electrons an atom possesses. For example, carbon has a valency of 4 because it has four valence electrons, while oxygen has a valency of 2 because it has six valence electrons and tends to gain two electrons to achieve stability.

Valency is crucial in predicting the formation of chemical compounds and understanding their bonding patterns. Elements with similar valencies often exhibit similar chemical behavior and tend to form compounds with each other. For instance, elements in Group 1 of the periodic table, such as lithium, sodium, and potassium, all have a valency of 1 and readily form compounds by losing one electron.

It is important to note that valency is not always fixed for an element. Some elements can exhibit multiple valencies depending on the specific compound or reaction. For example, iron can have a valency of 2 or 3 in different compounds, as it can lose either two or three electrons from its valence shell.

Comparison

While oxidation number and valency are related to the electron configuration of atoms, they have distinct characteristics and applications. Let's compare some of their attributes:

Definition

• Oxidation number: Hypothetical charge assigned to an atom in a compound, based on electron transfer.
• Valency: Combining capacity of an atom or ion, representing the number of electrons it can gain, lose, or share.

Value Type

• Oxidation number: Can be positive, negative, zero, or fractional/decimal.
• Valency: Always a whole number.

Relation to Charge

• Oxidation number: Not necessarily related to the actual charge of an atom in a compound.
• Valency: Often coincides with the actual charge of an atom in a compound.

Application

• Oxidation number: Balancing redox reactions, identifying oxidizing and reducing agents.
• Valency: Predicting compound formation, understanding bonding patterns.

Examples

Let's consider a few examples to illustrate the differences between oxidation number and valency:

In the compound H2SO4 (sulfuric acid), the oxidation number of sulfur is +6, while its valency is 2. The oxidation number of hydrogen is +1, and the oxidation number of oxygen is -2. However, the valency of hydrogen is 1, and the valency of oxygen is 2. This example demonstrates how oxidation numbers can be different from valencies, as they are based on electron transfer rather than combining capacity.

Another example is the compound FeCl3 (iron(III) chloride). The oxidation number of iron is +3, indicating the loss of three electrons, while its valency is 2. This discrepancy arises because iron can exhibit multiple oxidation states, but its valency is determined by the number of valence electrons it possesses.

Conclusion

Oxidation number and valency are both important concepts in chemistry that help us understand the behavior of elements and compounds. While oxidation number focuses on the hypothetical charge assigned to an atom based on electron transfer, valency describes the combining capacity of an atom or ion. They have different value types, applications, and relationships to the actual charge of an atom in a compound. Understanding these concepts is crucial for balancing redox reactions, predicting compound formation, and comprehending bonding patterns in chemistry.