Name: electron transfer in redox
Uploaded: 2019-03-11T09:21:00.000Z
Duration: 1 min 24 s
Channel: JoVE

K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Earth and Environmental Science

Earth's Systems

ESS.EES.3.1

Redox Reactions

Lors d'une réaction d'oxydo-réduction,ou réaction redox,des électrons sont transférés entre les atomes. 
La molécule qui cède l'électron est oxydée,et la molécule qui capte l'électron est réduite,ayant une charge moins positive. 
Par exemple, lorsque les atomes neutres dusodium et du chlore deviennent des ions,le sodium perd un électron, il est oxydé,et le chlore gagne un électron, il est réduit. 
De plus, la molécule qui cède un électronest appelée agent réducteur,tandis que la molécule qui reçoit l'électronest l'agent oxydant. 
Donc, le sodium est oxydé : c'est donc l'agent réducteur,et le chlore est réduit : c'est l'agent oxydant.

Flowers, P., Theopold, K., Langley, R., Robinson, W. R., Clark, M. A., Douglas, M., Choi, J. Section 4.2 : Classification des réactions chimiques. En chimie 2e. OpenStax. Houston, Texas (2019).

réactions d'oxydoréduction

Les réactions d’oxydation-réduction, ou redox, modifient l’état d’oxydation des atomes par le transfert d’électrons d’un atome, l’agent réducteur, vers un autre atome qui reçoit l’électron, l’agent oxydant. Ici, l’atome qui donne des électrons est oxydé — il perd des électrons — et l’atome qui accepte les électrons est réduit — il a une charge moins positive parce qu’il gagne des électrons. Le mouvement de l’énergie dans les réactions redox dépend du potentiel des atomes pour attirer les électrons liants — leur électronégativité. Si l’agent oxydant est plus électronégatif que l’agent réducteur, alors l’énergie est libérée. Toutefois, si l’agent oxydant est moins électronégatif que l’agent réducteur, l’apport d’énergie est nécessaire.
 
 <h4>Les agents réducteurs s’oxydent</h4>
 
 L’oxydation est-elle une perte ou un gain d’électrons ? La terminologie peut être déroutante. On utilise généralement l’acronyme OEP REG pour s’en souvenir. Il signifie que l’oxydation est une perte ; la réduction est un gain. Donc, si un atome est oxydé, alors il perd des électrons. En tant qu’agent réducteur, l’atome oxydé transfère des électrons vers un autre atome, ce qui le réduit. Avec OEP REG à l’esprit, on peut répondre à la plupart des questions sur les membres d’une réaction redox.
 
 <h4>L’électronégativité et l’énergie</h4>
 
 Les réactions redox produisent ou nécessitent de l’énergie. Si un atome cède un électron à un atome plus électronégatif, alors c’est une réaction énergétiquement favorable, et l’énergie est libérée. C’est en effet très logique — semblable à un homme fort gagnant un bras de fer avec un homme plus faible — parce qu’un atome plus électronégatif a une plus grande capacité à tirer des électrons vers lui. Un exemple biologique de ce type de réaction est la respiration cellulaire, dans laquelle l’énergie est libérée et utilisée pour créer l’ATP, une forme d’énergie que les cellules peuvent facilement utiliser.
 
 D’autres réactions redox ont besoin d’énergie, plutôt que d’en libérer. Si un électron passe d’un atome plus électronégatif à un atome moins électronégatif, de l’énergie doit être utilisée. C’est comme un homme plus faible qui gagne le bras de fer avec un homme plus fort, il faut de l’énergie d’une source extérieure. Un exemple biologique est la photosynthèse, dans laquelle les électrons sont transférés de l’eau au dioxyde de carbone à l’aide de l’énergie sous forme de lumière.
 
 <h4>Transfert incomplet d’électrons</h4>
 
 Une réaction redox peut se produire non seulement lorsqu’un électron est transféré, mais aussi lorsqu’il y a une modification au partage d’un électron dans une liaison covalente ! Par exemple, lorsque le méthane et l’oxygène réagissent, ils produisent du dioxyde de carbone et de l’eau. Dans ce cas, le carbone dans le méthane est oxydé. C’est parce que les électrons dans le méthane sont partagés de façon uniforme entre le carbone et l’hydrogène, alors que le carbone dans le dioxyde de carbone est partiellement positif puisque l’oxygène attire plus les électrons que ne le fait le carbone.

Réactions d'oxydoréduction

Les réactions d’oxydoréduction ou d’oxydoréduction impliquent le transfert d’électrons d’une molécule ou d’un atome à un autre. Lorsqu’un atome gagne un électron, un autre ...

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electron transfer in redox

Redox reactions are chemical reactions that involve electron transfer between atoms or molecules. When one particle gains electrons, another must lose them at the same time. That is why oxidation and reduction always happen together.

The two roles in a redox reaction are linked. The atom that is oxidized acts as the reducing agent, or reductant. The atom that is reduced acts as the oxidizing agent, or oxidant. A simple way to remember the ideas is OIL-RIG, which means oxidation is losing electrons and reduction is gaining electrons.

Redox reactions also change oxidation states, or oxidation numbers. An oxidation state is the charge an atom would have if all of its bonds were purely ionic. Checking whether oxidation numbers change in the reactants can help identify a redox reaction.

A sodium and chlorine reaction makes this idea clear. Sodium is oxidized, and chlorine is reduced to form sodium chloride. The process can be shown with half-reactions, which separate the fate of each reactant. In these equations, sodium goes from an oxidation number of 0 to 1+, while chlorine in Cl2 goes from 0 to 1-.

Electron transfer is not always complete. A redox reaction can also happen when the sharing of electrons changes in a covalent bond. Methane and oxygen can react to form carbon dioxide and water. In methane, electrons are shared equally between carbon and hydrogen, but in carbon dioxide the carbon is partially positive because oxygen pulls electrons more strongly. In that reaction, carbon dioxide is oxidized and oxygen is reduced.

Electron Transfer in Redox

the periodic table and organismal elements

the-periodic-table-and-organismal-elements

Periodic Table Basics for Living Things

The periodic table helps explain which elements living things need and how those elements are related. Elements are the smallest units of matter that cannot be broken down further by chemical processes. There are 118 known elements, but not all occur naturally, and even fewer are essential for life. Living matter is made mostly of carbon, nitrogen, hydrogen, and oxygen. Together, these elements make up most of the human body and are also found in all life on Earth. Smaller amounts of calcium,...

atomic structure

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electron behavior

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covalent bonds

Electronegativity and Covalent Bond Polarity

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ionic bonds

Ionic Compounds and Electrolytes

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hydrogen bonds

Hydrogen Bonds in Water

Hydrogen bonds in water are weak attractions between atoms that are already part of other chemical bonds. One atom is electronegative, such as oxygen, and carries a partial negative charge. The other is a hydrogen atom that is bonded to another electronegative atom and has a partial positive charge. These attractions form because hydrogen has very weak electronegativity when it binds with a strongly electronegative atom like oxygen or nitrogen. The electrons in that bond are shared unequally.

van der waals interactions

Intermolecular Forces in Polar Solutions

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elements and compounds

Elements, Compounds, and Bonding

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chemical reactions

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redox reactions

Redox reactions are chemical reactions that involve electron transfer between atoms or molecules. When one particle gains electrons, another must lose them at the same time. That is why oxidation and reduction always happen together. The two roles in a redox reaction are linked. The atom that is oxidized acts as the reducing agent, or reductant. The atom that is reduced acts as the oxidizing agent, or oxidant. A simple way to remember the ideas is OIL-RIG, which means oxidation is losing...

cohesion

Water Molecules and Surface Tension

Water molecules stick to each other through cohesion. Water is neutral overall, but it is a polar molecule. The oxygen atom in one water molecule has a partial negative charge, and it can bind with a hydrogen atom that has a partial positive charge in another water molecule. This forms a hydrogen bond. Each water molecule can form up to four hydrogen bonds with other water molecules, and these bonds give water its cohesive nature. Cohesion helps water form droplets on a surface. Water does not...

adhesion

Water Climbing by Adhesion

Water can climb or stick to surfaces because of adhesion, which is the attraction between different kinds of molecules. In water, this is easy to see on polar surfaces such as glass or cellulose in plants. The positive hydrogen side of water is more attracted to the negative oxygen in silica than to nearby water molecules. This attraction helps explain capillary action. If a narrow glass tube is placed in a beaker of water, water molecules attach to the tube’s surface and the water level rises.

states of water

Water Phase Changes and Ice Density

Water changes between solid, liquid, and gas states as temperature and molecular motion change. In this lesson, the focus is on how water freezes, melts, vaporizes, and returns to liquid or solid form. The balance between intermolecular forces, which pull molecules together, and kinetic energy, which pushes them apart, controls each state. Water freezes when intermolecular forces become stronger than kinetic energy. Unlike most substances, ice is less dense than liquid water. This happens...

specific heat

How Specific Heat Affects Temperature

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vaporization

Vaporization, Boiling, and Evaporation

Vaporization changes a liquid into vapor when temperature adds enough kinetic energy to overcome intermolecular forces. It is a surface phenomenon, which means it starts at the liquid’s surface. The energy needed to vaporize a set amount of liquid at a given pressure and constant temperature is called the heat of vaporization. Water shows this process clearly. When liquid water is vaporized, it becomes steam. One way this happens is boiling, which occurs when vapor bubbles form beneath the...

solvents

Water as a Biological Solvent

Water acts as a biological solvent in many living systems. A solvent is a substance, usually a liquid, that dissolves another substance called a solute. When a solvent and a solute mix, they form a solution, which is a uniform mixture of both parts. Water is called a universal biological solvent because its polar structure helps it dissolve many other polar compounds. Polarity means that one side of the molecule has a slight positive charge and the other side has a slight negative charge.

carbon skeletons

Carbon Backbones in Biomolecules

Carbon backbones give biological molecules their structure and flexibility. Living things are built from macromolecules that contain carbon atoms, and organic compounds are defined by a carbon backbone. Carbon is tetravalent, so each carbon atom can bond with four other atoms. Its valence electrons are stable, so carbon rarely becomes an ion. As carbon chains get longer, they can form ring structures, double bonds, and branching side chains. Carbon-carbon bonds create the carbon skeleton.

key terms and concepts

Learn how redox reactions move electrons, change oxidation states, and use half-reactions to track sodium, chlorine, methane, and oxygen.

Electron Transfer in Redox | JoVE K12

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Electron Transfer in Redox

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