# What is the Oxidation Number of Phosphorus and How to find It

Phosphorus's oxidation number indicates its charge in compounds. By following rules, we can find it and understand its chemical role.

Sarah Taylor-

Published on 2023-06-07

## Introduction

In the field of chemistry, oxidation numbers play a crucial role in understanding the behavior of elements within compounds. Phosphorus is a versatile element with various oxidation states, making it an intriguing subject of study. In this article, we will explore the concept of oxidation numbers, delve into the oxidation number of phosphorus, and learn how to calculate it.

## Understanding Oxidation Numbers

Oxidation numbers, also known as oxidation states, are assigned to atoms within a compound to represent the charge that an atom would possess if the compound were composed of ions. These numbers aid in understanding electron distribution and the transfer of charges between atoms.

## Oxidation Number of Phosphorus

Phosphorus is an element with multiple oxidation states, which means it can exhibit different oxidation numbers depending on the compound it is present in. To determine the oxidation number of phosphorus in a compound, we need to apply a set of rules and considerations.

## Finding the Oxidation Number for Phosphorus

### Rule for Oxygen:

In most compounds, oxygen has an oxidation number of -2, unless it is combined with a more electronegative element. For the purpose of calculating the oxidation number of phosphorus, we can assume that oxygen has an oxidation number of -2.

### Rule for the Overall Charge of the Compound:

The overall charge of a compound must be zero for neutral compounds. The sum of the oxidation numbers of all atoms in a neutral compound should add up to zero.

### Rule for Hydrogen:

Hydrogen typically has an oxidation number of +1, except when it is combined with a more electronegative element, such as phosphorus.

### Calculation

To calculate the oxidation number of phosphorus (P) in a compound, we can utilize the information obtained from the aforementioned rules. Let's denote the oxidation number of phosphorus as x.

Considering a compound that contains oxygen and hydrogen, we need to account for their oxidation numbers. For example, in the compound H3PO4 (phosphoric acid), we know that there are four oxygen atoms, each with an oxidation number of -2, and three hydrogen atoms, each with an oxidation number of +1.

Applying the rule for the overall charge of the compound (zero), we can set up the equation: x + 3(+1) + 4(-2) = 0.

Simplifying the equation, we get: x + 3 - 8 = 0.

Solving for x, we find that the oxidation number of phosphorus in H3PO4 is +5. Therefore, in this compound, phosphorus has an oxidation number of +5.

## Importance of Oxidation Numbers

Understanding the oxidation number of an element, such as phosphorus, is vital in predicting its behavior in chemical reactions. It assists in balancing equations, identifying the type of reaction, and determining the reducing and oxidizing agents involved.

## Additional Examples of Phosphorus Oxidation Numbers

To further illustrate the concept of phosphorus oxidation numbers, let's consider a few additional examples:

### Phosphine (PH3):

In phosphine, which is a compound containing phosphorus and hydrogen, hydrogen has an oxidation number of +1. Since the compound is neutral, the sum of the oxidation numbers should equal zero. Therefore, in PH3, the oxidation number of phosphorus is -3.

### Phosphorus Pentoxide (P2O5):

In phosphorus pentoxide, there are five oxygen atoms, each with an oxidation number of -2. Applying the rule for the overall charge of the compound (zero), we can set up the equation: 2x + 5(-2) = 0. Simplifying the equation, we get: 2x - 10 = 0. Solving for x, we find that the oxidation number of phosphorus in P2O5 is +5.

## Conclusion

In conclusion, the oxidation number of phosphorus can vary depending on the compound it is present in. By applying the rules and calculations discussed above, we can determine the oxidation number of phosphorus in different compounds. Understanding oxidation numbers is essential for predicting the behavior of elements in chemical reactions and for a comprehensive understanding of their role within compounds.