Name: electron regions in atomic orbitals
Uploaded: 2020-09-03T13:38:27.000Z
Duration: 2 min 44 s
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Atomic Orbitals

La région la plus dense du nuage d'électrons où un électron est le plus susceptible d'être trouvé est décrite en termes d'orbitales atomiques. La forme d'une orbitale atomique est déterminée par le nombre quantique de moment angulaire, l. Rappelons que les valeurs de l sont basées sur le nombre quantique principal n les valeurs possibles de l vont de zéro à n moins un.Lorsque n est supérieur à un, plusieurs sous-niveaux existent. Chaque valeur de l correspond à une orbitale s, p, d ou f. L'orbitale d'énergie la plus basse est l'orbitale 1-s.C'est une orbitale sphérique symétrique. La densité de probabilité d'une orbitale 1-s révèle que l'électron est le plus susceptible d'être trouvé au niveau du noyau. Cependant, étant donné les forces électrostatiques entre les protons et les électrons-ce n'est pas probable.Multiplier la densité de probabilité par le volume des shells sphériques minces avec des rayons r est plus représentatif. La probabilité totale de trouver un électron dans le shell mince à une distance r du noyau est la fonction de distribution radiale. Pour l'hydrogène, la plus grande probabilité de trouver un électron est à 52, 9 picomètres du noyau.Ainsi, la forme de l'orbitale atomique 1-s pour l'hydrogène est sphérique avec un rayon de 52, 9 picomètres. Les orbitales deux-s et trois-s sont également sphériques. Ils sont plus grands et ont des nœuds.À un nœud, la probabilité de trouver un électron est nulle. Les niveaux principaux avec n égal à deux ou plus contiennent également trois orbitales p. Ceux-ci sont en forme de lobe avec un nœud au niveau du noyau.Leur orientation est décrite par la valeur de m-l. Les trois orbitales p sont orthogonales l'une à l'autre. Les niveaux principaux de n égaux à trois ou plus ont également cinq orbitales d.Les orbitales d en forme de feuille de trèfle ont quatre lobes denses aux électrons et deux plans nodaux perpendiculaires. L'un des d-orbitales est légèrement différente. Les orbitales f ont plus de lobes et de nœuds.Ces orbitales existent pour les niveaux principaux de n égal à quatre ou plus. Lorsque vous superposez les orbitales les unes sur les autres, une forme à peu près sphérique émerge. C'est pourquoi les atomes sont généralement représentés comme des sphères.

orbitales atomiques

Une orbitale atomique représente les régions tridimensionnelles d'un atome où un électron a la plus grande probabilité de demeurer. La fonction de distribution radiale indique la probabilité totale de trouver un électron sur la couche mince à une distance r du noyau. Les orbitales atomiques ont des formes distinctes qui sont déterminées par l, le nombre quantique du moment angulaire. Les orbitales sont souvent représentées par une surface limite, qui renferme les régions les plus denses du nuage.  
 
 Le nombre quantique du moment angulaire est un nombre entier qui peut prendre les valeurs, l = 0, 1, 2, …, n – 1. Une orbitale dont le nombre quantique principal est 1 (n = 1) ne peut avoir qu'une seule valeur de l (l = 0), alors qu'un nombre quantique principal de 2 (n = 2) permet l = 0 et l = 1. Les orbitales ayant la même valeur de l définissent une sous-couche. 
 
 Les orbitales dont l = 0 sont appelées les orbitales s et elles constituent les sous-couches s. La valeur l = 1 correspond aux orbitales p. Pour un n donné, les orbitales p constituent une sous-couche p (c.-à-d., 3p si n = 3). Les orbitales dont l = 2 sont appelées les orbitales d. Les orbitales dont l = 3, 4 et 5 sont les orbitales f, g et h. 
 
 L'orbitale d'énergie la plus basse est l'orbitale 1s. Il s'agit d'une orbitale de symétrie sphérique. La densité de probabilité de présence (ψ2) d'une orbitale 1s implique que l'électron est le plus susceptible d'être trouvé au noyau. Cependant, étant donné les forces électrostatiques entre les protons et les électrons, cela ne représente pas précisément l'emplacement de l'électron. Au lieu de cela, la fonction de distribution radiale est utilisée, qui est un tracé de la probabilité totale de trouver un électron dans une orbitale à un rayon r donné. La fonction de distribution radiale est trouvée en multipliant la densité de probabilité par le volume des couches sphériques minces avec les rayons, r. Pour l'orbitale 1s de l'hydrogène, la fonction de distribution radiale a une valeur nulle au niveau du noyau, qui augmente jusqu'à un maximum à 52,9 picomètres avant de diminuer avec l'augmentation de r.
 
 Il y a certaines distances du noyau auxquelles la densité de probabilité de trouver un électron situé sur une orbitale particulière est nulle. En d'autres termes, la valeur de la fonction d'onde ψ est nulle à cette distance pour cette orbitale. Une telle valeur de r est appelée un nœud radial. Le nombre de nœuds radiaux dans une orbitale est de n – l – 1. Pour les orbitales 2s, où n = 1, il y a un nœud radial, alors que les orbitales 3s ont deux nœuds radiaux.  
 
 Chaque niveau principal dont n = 2 ou plus contient trois orbitales p. Les trois orbitales p ont deux lobes avec un nœud situé au niveau du noyau. L'orientation des orbitales p dans l'espace est décrite par la valeur de ml. Les trois orbitales p sont mutuellement perpendiculaires (orthogonales) les unes aux autres. Les orbitales p plus hautes (3p, 4p, 5p et plus) ont des formes similaires mais sont plus grandes avec des nœuds radiaux supplémentaires. 
 
 Les niveaux principaux dont n = 3 ou plus contiennent cinq orbitales d. Quatre de ces orbitales ont une forme de trèfle, avec quatre lobes de densité d'électrons. Il existe deux plans nodaux perpendiculaires qui se croisent au noyau. Au niveau de ces plans nodaux, la densité électronique est nulle. L'une des orbitale d a une forme légèrement différente et a deux lobes orientés sur l'axe des z avec un anneau en forme de beignet dans le plan xy. Les principaux niveaux dont n = 4 et plus contiennent sept orbitales f, qui ont des formes complexes. Ces orbitales ont plus de nœuds et de lobes que les orbitales d.
 
 <img alt="Figure1" src="https://www.jovecore.com/CDNSource/lessons/983/983Image 1.png" style="width: 700px;" />
 
 Figure 1 : orbitales s, p, d et f représentatives. 
 
 Ces différentes formes des orbitales atomiques représentent les régions tridimensionnelles dans lesquelles l'électron est susceptible d'être trouvé. Les orbitales toutes ensemble constituent une forme à peu près sphérique, ce qui explique pourquoi les atomes sont généralement représentés comme des sphères. 
 
 Ce texte est adapté de <a href="https://openstax.org/books/chemistry-2e/pages/6-3-development-of-quantum-theory">Openstax, Chimie 2e, Section 6.3 : Développement de la théorie quantique.</a>

Orbitales atomiques

Une orbitale atomique représente les régions tridimensionnelles d’un atome où un électron a la plus grande probabilité de résider. La distribution radiale ...

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electron regions in atomic orbitals

Electron regions in atomic orbitals show where an electron is most likely to be found in an atom. These three-dimensional regions are often drawn as boundary surfaces around the densest part of the cloud.

The shape of an orbital depends on the angular momentum quantum number, l. This value can range from 0 to n - 1, where n is the principal quantum number. For n = 1, only l = 0 is allowed. For n = 2, both l = 0 and l = 1 are allowed.

Orbitals with the same value of l form a subshell. The l = 0 orbitals are s orbitals, and they make up s subshells. The l = 1 orbitals are p orbitals, which form a p subshell such as 3p when n = 3. The l = 2 orbitals are d orbitals. The l = 3, 4, and 5 orbitals are called f, g, and h orbitals.

The lowest-energy orbital is the 1s orbital. It is spherically symmetric. The probability density, ψ², suggests that an electron is most likely found at the nucleus. But this does not fully match electron behavior. The radial distribution function gives the total probability of finding an electron at a distance r from the nucleus. It is found by multiplying the probability density by the volume of thin spherical shells.

For the 1s orbital of hydrogen, the radial distribution function is zero at the nucleus. It rises to a maximum at 52.9 picometers and then decreases as r increases. Some distances from the nucleus have zero probability density for a given orbital. These points are called radial nodes. The number of radial nodes is n - l - 1. A 2s orbital has one radial node, and a 3s orbital has two.

Each principal level with n = 2 or more contains three p orbitals. Each p orbital has two lobes and a node at the nucleus. Their orientation in space is described by m_l. The three p orbitals are mutually perpendicular. Higher p orbitals, such as 3p, 4p, and 5p, have the same general shape but are larger and contain additional radial nodes.

Principal levels with n = 3 or more contain five d orbitals. Four of them have a cloverleaf shape with four electron-dense lobes. They also have two perpendicular nodal planes that meet at the nucleus. The fifth d orbital has two lobes along the z-axis and a donut-shaped ring in the xy plane.

Principal levels with n = 4 and greater contain seven f orbitals. These orbitals have complex shapes with more nodes and lobes than d orbitals. Together, s, p, d, and f orbitals help explain why atoms are often drawn as spheres, even though the electron regions inside them have distinct shapes.

Electron Regions in Atomic Orbitals

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Explore electron regions in atomic orbitals, including s, p, d, and f shapes, radial nodes, and the radial distribution function for high school chemistry.

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Electron Regions in Atomic Orbitals

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