Name: electronegativity in polar covalent bonds
Uploaded: 2025-05-22T09:05:32.000Z
Duration: 2 min 24 s
Channel: JoVE

K12 Standards

Arizona Science Standards

High School

Physical Science

HS.P1

HS.P1U1.2

Polar Covalent Bonds

Les non-métaux ont des énergies d’ionisation élevées, ce qui rend difficile le transfert d’électrons de valence d’un atome à un autre. Par conséquent, les non-métaux ont tendance à partager des électrons de valence entre les atomes, formant des liaisons covalentes.
La paire d’électrons partagée dans la liaison covalente est appelée paire de liaison. Tous les électrons de valence qui ne participent pas à la liaison sont appelés le doublet non liant, ou électrons non liants.
Selon la règle de l’octet, lorsque certains atomes ont moins de huit électrons dans leur couche de valence, ils réagissent pour former des composés stables en atteignant la configuration du gaz noble le plus proche.
Par exemple, dans une molécule d’ammoniac, l’azote a besoin de trois électrons supplémentaires pour atteindre sa configuration de gaz noble la plus proche, ou un octet, tandis que l’hydrogène a besoin d’un électron de plus pour atteindre sa configuration de gaz noble la plus proche, ou un duo. Ainsi, l’atome d’azote forme des liaisons simples avec trois atomes d’hydrogène.
D’autre part, les molécules de dioxyde de carbone et de monoxyde de carbone sont maintenues ensemble par des liaisons doubles et triples carbone-oxygène, respectivement. La formation des liaisons doubles et triples garantit que chacun des atomes constitutifs atteint la configuration de gaz noble la plus proche.
Lorsque des liaisons covalentes se forment entre deux atomes d’éléments différents, l’atome le plus électronégatif attire plus fortement les électrons, formant une liaison covalente polaire. La capacité d’un atome à attirer des électrons vers lui-même est appelée électronégativité. Plus la différence d’électronégativité est grande, plus le lien sera polaire.
L’échelle de Pauling fournit la valeur d’électronégativité de chaque élément sur la base des calculs d’énergie de liaison. L’azote est plus électronégatif que le carbone, qui à son tour est plus électronégatif que l’hydrogène.
Ainsi, dans une liaison covalente entre le carbone et l’azote, plus l’azote électronégatif attire les électrons partagés vers lui, tandis que, dans une liaison entre le carbone et l’hydrogène, plus le carbone électronégatif attire la densité électronique loin de l’hydrogène moins électronégatif.

Adapté de <a href="https://openstax.org/books/chemistry-2e/pages/7-2-covalent-bonding">Openstax, Chimie 2e, Section 7.2 : Liaisons covalentes</a>

liaisons covalentes polaires

Les liaisons covalentes se forment entre deux atomes lorsque les deux ont des tendances similaires à attirer les électrons vers eux-mêmes (c'est-à-dire lorsque les deux atomes ont des énergies d'ionisation et des affinités électroniques identiques ou assez similaires). Les atomes non métalliques forment souvent des liaisons covalentes avec d'autres atomes non métalliques. Par exemple, la molécule d'hydrogène, H2, contient une liaison covalente entre ses deux atomes d'hydrogène. Lorsque deux atomes d'hydrogène distincts avec une énergie potentielle particulière s'approchent l'un de l'autre, leurs orbitales de valence (1s) commencent à se chevaucher. Les électrons simples sur chaque atome d'hydrogène interagissent alors avec les deux noyaux atomiques, occupant l'espace autour des deux atomes. La forte attraction de chaque électron partagé vers les deux noyaux stabilise le système, et l'énergie potentielle diminue à mesure que la distance de liaison diminue. Si les atomes continuent à se rapprocher, les charges positives des deux noyaux commencent à se repousser, et l'énergie potentielle augmente. La longueur de liaison est déterminée par la distance à laquelle l'énergie potentielle la plus faible est atteinte. Le fait que la liaison soit non polaire ou polaire covalente est déterminé par une propriété des atomes de liaison appelée électronégativité.

Les valeurs d'électronégativité des éléments ont été proposées par l'un des chimistes les plus célèbres du XXe siècle : Linus Pauling. L'électronégativité est une mesure de la tendance d'un atome à attirer les électrons (ou la densité électronique) vers lui-même. L'électronégativité détermine comment les électrons partagés sont répartis entre les deux atomes d'une liaison. Plus un atome attire fortement les électrons dans ses liaisons, plus son électronégativité est grande. Elle décrit à quel point un atome attire étroitement les électrons dans une liaison. C'est une grandeur sans dimension qui est calculée, et non mesurée. Pauling a dérivé les premières valeurs d'électronégativité en comparant les quantités d'énergie nécessaires pour rompre différents types de liaisons. Les électrons dans une liaison covalente polaire sont déplacés vers l'atome le plus électronégatif ; ainsi, l'atome le plus électronégatif est celui avec la charge partielle négative. Plus la différence d'électronégativité est grande, plus la distribution des électrons est polarisée et plus les charges partielles des atomes sont importantes.

Liaisons covalentes polaires

Les liaisons covalentes se forment entre deux atomes lorsque les deux ont des tendances similaires à attirer les électrons à eux-mêmes (c’est-à-dire lorsque les deux atomes ont des ...

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Organic Chemistry

Chimie organique

Unit 1

Unité 1

Covalent Bonding and Structure

Liaison covalente et structure

KEY TERMS AND CONCEPTS

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electronegativity in polar covalent bonds

Polar covalent bonds form when atoms share electrons unevenly. This happens in covalent bonds between atoms that have similar, but not identical, tendencies to attract electrons. Nonmetal atoms often make these bonds with other nonmetals. Hydrogen gas, H2, is a simple example of a covalent bond between two hydrogen atoms.

A covalent bond begins when two atoms move close enough for their valence orbitals to overlap. In hydrogen, the 1s orbitals overlap and the single electrons on each atom interact with both nuclei. The shared electrons are attracted to both nuclei, which lowers the potential energy of the system. As the atoms get closer, the bond reaches its length at the point of lowest potential energy.

If the atoms move too close, the positive nuclei begin to repel each other. That repulsion raises the potential energy. The balance between attraction and repulsion sets the bond length. This balance helps explain why covalent bonds are stable at a specific distance.

Whether a covalent bond is polar or nonpolar depends on electronegativity. Electronegativity is an atom’s tendency to attract electron density toward itself. It is a calculated, dimensionless value, not a measured one. Linus Pauling proposed the first electronegativity values by comparing the energy needed to break different bonds.

In a polar covalent bond, the shared electrons shift toward the more electronegative atom. That atom carries the partial negative charge. The other atom carries the partial positive charge. When the electronegativity difference is larger, the bond becomes more polarized and the partial charges become larger.

Electronegativity in Polar Covalent Bonds

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Learn how electronegativity affects polar covalent bonds, why electrons shift unevenly, and how partial charges form in shared bonds like H2.

Electronegativity in Polar Covalent Bonds | JoVE K12

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Electronegativity in Polar Covalent Bonds

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