This short video will explain oxidation-reduction reactions, or redox reactions for short.
The focus is on how electrons are transferred during redox reactions. Learn some neat mnemonic devices to help you remember when an atom is oxidizing or reducing.
Reduction and Oxidation
Are you familiar with the reaction that forms table salt? Do you know what kind of reaction it is? This lesson is Redox Reactions and is part of the review of inorganic chemistry.There is a specific type of chemical reaction called oxidation-reduction reactions (or redox reactions for short).
In these reactions, electrons are transferred from one reactant to another. So, simply put, electrons are lost from one substance and gained by another.Oxidation refers to the loss of electrons from a substance, while reduction refers to the gain of electrons by a substance. These two processes cannot occur without the other. That being said, if there’s a reduction reaction, there must be an oxidation reaction.
Or, if there’s an oxidation reaction, there must be a reduction reaction. Don’t be confused by reduction being a gain, though. Adding electrons is called reduction because the overall charge is reduced – more electrons means the substance becomes more negative.For example, carbon typically has six protons, six neutrons and six electrons.
If we reduce carbon, it gains an electron. If you remember, electrons are negative, so adding another electron would make seven, and the carbon atom would become more negative. We would say that the carbon’s overall charge has decreased, or it has been reduced.An easy way to keep it straight is by using the mnemonic device ‘LEO the lion says GER.
‘ LEO stands for ‘lose electrons oxidation.’ GER stands for ‘gain electrons reduction.’ So, oxidation is when an atom loses electrons, while reduction is when an atom gains electrons.
Redox Reaction Examples
The easiest way to fully understand redox reactions is to look at some examples. So let’s start by looking at the reaction that forms table salt. Sodium is oxidized and loses an electron to have a +1 charge; meanwhile chlorine is reduced because it gains the electron to have a -1 charge. The redox reaction creates two ions with opposite charges that are attracted to one another and create sodium chloride, or table salt.At this point it’s also important to discuss reducing and oxidizing agents. A reducing agent donates electrons or reduces another substance. So, in the case of our table salt reaction, sodium is the reducing agent.
An oxidizing agent accepts electrons or oxidizes another substance. So, in the case of our table salt reaction, chlorine is the oxidizing agent. An oxidizing agent gains electrons, and an oxidizing agent is reduced.A silly mnemonic device to help you remember this is ‘Ryan already likes eating ostriches. Ostriches are getting eaten regularly.
‘ The mnemonic stands for a reducing agent loses electrons and is oxidized, while an oxidizing agent gains electrons and is reduced.
Another example of a redox reaction is the formation of hydrogen fluoride. We can break the reaction down to analyze the oxidation and reduction of reactants.
The hydrogen is oxidized and loses two electrons, so each hydrogen becomes positive. The two electrons are gained by fluorine, which is reduced. This makes the two fluorines negative. The oxidation of hydrogen and reduction of fluorine creates two ions with opposite charges of +1 and -1.
Opposites attract, so they combine and form hydrogen fluoride.But not all redox reactions are cut and dry with gaining and losing electrons; electron sharing exists with covalent bonding. With covalently bonded molecules, whether a substance oxidizes or reduces is based on the atom’s pull on electrons, or electronegativity. Electronegativity is the attractive force that an atom exerts on electrons. It’s based on the atomic number and the distance of valence electrons in an atom.
We’ve already talked about electronegativity when discussing bonding. When atoms have similar electronegativity, they use nonpolar covalent bonding. But, in ionic bonding, the two atoms have very different electronegativity numbers, leading to them exchanging an electron. Then, when electronegativity numbers are somewhere in the middle, the atoms will form polar covalent bonds.For example, consider a reaction between methane and chlorine. Methane and chlorine react to form chloromethane and hydrochloric acid. The atoms in both reactant molecules are covalently bonded.
The carbon atom in the methane molecule has a slightly higher electronegativity than the hydrogen atoms, so it exerts a slight pull on the electrons. The electrons in the chlorine molecule are shared equally because each chlorine atom has the same pull (or electronegativity). Once the two molecules react with each other, the electrons in chloromethane and in hydrochloric acid are not shared evenly.
In the reaction, one atom has been reduced and one atom has been oxidized. Which is which? Because chlorine is a very electronegative atom, it exerts a stronger pull on the electrons in each new molecule. This can be viewed as gaining electrons (or reduction).
So, the reactant chlorine is the oxidizing agent in this reaction, and it goes through reduction to form both chloromethane and hydrochloric acid. Conversely, methane is a classic reducing agent. The carbon and hydrogen have a low electronegativity (as compared to chlorine), so they gladly donate electrons to the chlorines.
The methane molecule is oxidized during the reaction since it has less of a pull on the electrons than chlorine.
So, let’s recap. Oxidation-reduction reactions involve the gaining and losing of electrons by reactants. They’re called redox reactions for short. An easy way to remember this is by using the mnemonic device ‘LEO the lion says GER.’ LEO stands for lose electrons oxidation, while GER stands for gain electrons reduction.
When determining the oxidizing and reducing agents in a reaction, consider whether the reactant gains or loses electrons. Reducing agents lose electrons, while oxidizing agents gain electrons. However, in some cases, electrons are shared by atoms (such as in covalent bonding).
When these molecules are involved in redox reactions, you must look at the uneven sharing, or pull, of the electrons between atoms. This is referred to as electronegativity. This will help you determine which substance is being oxidized and which is being reduced. The pull can be interpreted as a gain or loss of electrons.
After this lesson, you should be able to:
- Explain oxidation-reduction reactions
- Recite the mnemonic for these reactions
- Describe how to determine which is the oxidizing agent and which is the reducing agent when covalent bonding is involved