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How To Find Oxidation Number?

Written by:
Reviewed by: Philip Calahan
How To Find Oxidation Number?

Have you ever wondered how chemists determine the oxidation number of a particular element in a compound? Understanding oxidation numbers is crucial for predicting chemical reactions and identifying the types of bonds between atoms. Although it may seem daunting at first, determining the oxidation number of an element is actually quite simple and can be done using a few basic rules. In this article, we will guide you through the process of finding oxidation numbers and explain the significance of these numbers in the world of chemistry.

1. Introduction: Understanding the Oxidation Number and Its Importance in Chemistry

As we dive into the world of chemistry, it’s essential to understand the concept of oxidation numbers. Sometimes called oxidation states, these numbers represent an atom’s electrons and are used to track the transfer of electrons during chemical reactions. The oxidation number is the charge that an atom would have if electrons were transferred completely from the atom of one element to the atom of another element.

Oxidation numbers are essential as they help determine the direction and feasibility of a chemical reaction. In simple terms, they can tell us whether a compound will oxidize or reduce. This understanding is crucial in predicting how chemicals will react and designing new compounds. Additionally, oxidation numbers are used to name compounds, particularly those with transition metals, and to write chemical equations. Understanding oxidation numbers is also necessary when studying redox reactions, a type of chemical reaction where electrons are transferred.

Overall, understanding the concept of oxidation numbers is vital in chemistry. It allows scientists to predict chemical reactions and design new compounds with specific properties. In the next section, we will dive deeper into the rules and guidelines for assigning oxidation numbers to atoms in a compound.

2. Rules for Finding Oxidation Numbers in Elements and Compounds

Once you understand the basics of oxidation numbers, they’re easy to determine for most elements and compounds. Here are the rules that can be applied to determine oxidation numbers:

1. The oxidation number of an uncombined element is always 0.
2. For ions, the oxidation number is equal to the charge of the ion.
3. The oxidation number of oxygen in most compounds is -2, except in peroxides where it is -1 and in OF2 (oxygen difluoride) where it is +2.
4. The oxidation number of hydrogen is usually +1 in compounds, except in metal hydrides where it is -1.
5. For a neutral compound, the sum of the oxidation numbers of all atoms equals zero.
6. For a polyatomic ion, the sum of the oxidation numbers of all atoms equals the charge of the ion.

These rules are just a starting point, there are always exceptions and special cases, so it’s important to check with a reference or textbook when in doubt.

It’s also important to note that oxidation numbers are just a formalism used to help us understand chemical reactions, and they don’t necessarily correspond to real electron configurations of atoms or molecules. However, they are useful for balancing redox reactions and predicting the behavior of certain compounds. With practice, determining oxidation numbers will become second nature and you’ll be able to apply these rules without even thinking about it.

3. Practical Examples of Finding Oxidation Numbers

After understanding the rules for assigning oxidation numbers, practical examples can help solidify the concept. Here are a few examples to help you understand the methodology behind determining oxidation numbers:

1. In NaCl (sodium chloride), sodium has a lower electronegativity than chlorine. Therefore, it loses an electron to chlorine’s outermost shell, making sodium’s oxidation number +1, and chlorine’s oxidation number -1.

2. In H2SO4 (sulphuric acid), hydrogen atoms have a +1 oxidation number. Since oxygen has -2 as the oxidation number, then sulfur atom’s oxidation number can be seen as follows:

2* (+1) + x + 4* (-2) = 0

This simplifies to:

+2 + x -8 = 0

From which we solve to generate an oxidation number for sulfur of +6.

3. In KMnO4 (potassium permanganate), potassium has an oxidation number of +1. Since oxygen has an oxidation number of -2 and there are four oxygen atoms, the total oxidation number from oxygen is -8. That leaves the manganese atom with an oxidation number of +7.

In conclusion, it is necessary to keep practicing various examples to gain confidence in assigning oxidation numbers, which are essential for many practical applications in chemistry.

4. Calculating Oxidation Numbers in Complex Molecules

When it comes to complex molecules, calculating oxidation numbers can be a daunting task. However, understanding oxidation numbers is crucial in predicting reaction outcomes and identifying chemical trends. Here are some steps to follow when :

1. Determine the oxidation states of known atoms:
Start by identifying the atoms in the molecule and their respective oxidation numbers. Remember that atoms in their elemental form have an oxidation number of 0. Also, keep in mind that hydrogen always has an oxidation number of +1 and oxygen has an oxidation number of -2, except in peroxides, where it has an oxidation number of -1.

2. Compute the oxidation state of unknown atoms:
Use the total charge of the molecule to determine the oxidation state of the unknown atoms. For example, in a neutral molecule, the sum of all oxidation numbers must be 0. If the molecule is an ion, the sum of all oxidation numbers must equal the charge of the ion.

3. Check the oxidation state of element groups:
Be mindful of elements that typically have the same oxidation state, such as alkali metals with +1 and alkaline earth metals with +2.

4. Use rules of electronegativity:
In some cases, electronegativity can help determine an atom’s oxidation state. For instance, if an element has a higher electronegativity than another element in the compound, it is expected to have a negative oxidation number.

Following these steps will help you to calculate the oxidation numbers in complex molecules accurately. Remember to practice regularly and seek further guidance if you require additional support.

5. Common Misconceptions about Oxidation Numbers and Techniques to Avoid Them

When it comes to chemistry, oxidation numbers play an essential role in determining the chemical properties of elements and compounds. Unfortunately, many misconceptions surround this concept, leading to confusion and potential errors. Here are some common misconceptions and techniques to avoid them:

1. The oxidation number always corresponds to the number of electrons gained or lost: This is not always true. The oxidation number can also represent the hypothetical charge an atom would have if the compound was ionic. Therefore, it is important to understand the context of the compound and its molecular structure.

2. The oxidation number of an atom in a compound is always positive: This is also incorrect. The oxidation number can be negative or zero, depending on the electronegativity of the atom and its shared electrons. For example, in hydrogen peroxide, the oxidation number of oxygen is -1.

Techniques to avoid these misconceptions include practicing exercises and understanding the fundamental principles of electron transfer and bonding. It can also help to approach the problem systematically, identifying the central atom, applying the rules of oxidation numbers, and balancing the equation. Finally, it is essential to double-check your work and seek help if needed. Remember, mastering oxidation numbers can take time and practice, but it is a critical skill for success in chemistry.

People Also Ask

What is oxidation number?

Oxidation number is a measure of the number of electrons that an atom gains or loses in a chemical reaction. It is a way of keeping track of the electron transfer between atoms.

How do you find oxidation number?

To find the oxidation number of an atom, you need to know the oxidation rules for the elements involved. You then assign the electrons based on these rules, taking into account any charges if the compound is an ion.

What are the rules for assigning oxidation numbers?

The oxidation numbers for most elements are their usual valences. Some rules include the following: hydrogen is +1, oxygen is -2, and the sum of the oxidation numbers in a compound equals zero. For ions, the sum of the oxidation numbers equals the charge of the ion.

Can an atom have multiple oxidation numbers?

Yes, an atom can have multiple oxidation numbers, depending on the compound it is in. For example, iron can have oxidation numbers of +2 or +3, depending on the compound.

What is the importance of knowing oxidation numbers?

Knowing the oxidation number is important for predicting the reactivity and behavior of compounds in chemical reactions. It also helps in balancing chemical equations and determining the electron transfer in redox reactions.


Finding the oxidation number of an atom is an important part of understanding the properties of compounds and predicting how they will behave in chemical reactions. By following the basic rules for assigning oxidation numbers, it becomes possible to determine the electron transfer and balance chemical equations.

Paul McCoy

Paul McCoy

Content Marketing Manager
In addition to my expertise as a Content Marketing Manager, I've also honed my skills in editorial processes and content curation through my role as an Editor at Dude Ask, a leading digital platform. At Dude Ask, I've spearheaded editorial initiatives, overseeing the publication of high-quality content and ensuring consistency in tone and messaging across all channels. My experience in editorial management has equipped me with a keen eye for detail and a knack for refining content to resonate with diverse audiences. Leveraging my passion for storytelling and deep understanding of audience behavior, I collaborate closely with writers and contributors to craft compelling narratives that captivate and inspire action. My tenure at Dude Ask has further solidified my commitment to driving engagement and growth through strategic content initiatives, positioning me as a versatile leader in the dynamic landscape of digital marketing and editorial management.

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