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

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IPC.7

IPC.7.E

Atomic Orbitals

La regione più densa della nuvola di elettroni, dove è più probabile che si trovi un elettrone, è descritta in termini di orbitali atomici. La forma di un orbitale atomico è determinata dal numero quantico del momento angolare, l. Ricordate che i valori di l sono basati sul numero quantico principale, n i possibili valori di l vanno da zero a n meno uno.

Quando n è maggiore di uno, esistono più sottolivelli. Ogni valore di l corrisponde ad un orbitale s, p, d o f. L'orbitale a energia più bassa è l'orbitale 1 s.

Questo è un orbitale sfericamente simmetrico. La densità di probabilità di un orbitale 1 s rivela che è più probabile che l'elettrone si trovi nel nucleo. Tuttavia, date le forze elettrostatiche fra protoni ed elettroni, questo non è probabile.

La moltiplicazione della densità di probabilità per il volume dei gusci sferici sottili con raggi r è più rappresentativa. La probabilità totale di trovare un elettrone all'interno del guscio sottile ad una distanza r dal nucleo è una funzione della distribuzione radiale. Per l'idrogeno, la più grande probabilità di trovare un elettrone è a 52, 9 picometri dal nucleo.

Pertanto, la forma dell'orbitale atomico 1-s per l'idrogeno è sferica con un raggio di 52, 9 picometri. Anche gli orbitali di due-s e tre-s sono sferici. Sono più grandi e possiedono nodi.

In un nodo, la probabilità di trovare un elettrone è zero. I livelli principali con n uguale a due o più contengono anche tre orbitali p. Questi ultimi sono a forma di lobo, con un nodo nel nucleo.

Il loro orientamento è descritto dal valore di m-l. I tre orbitali p sono ortogonali fra di loro. I livelli principali di n uguali a tre o più hanno anche cinque orbitali d.

Gli orbitali d, con forma a quadrifoglio, hanno quattro lobi densi di elettroni e due piani nodali perpendicolari. Uno degli orbitali d è leggermente diverso. Gli orbitali f hanno più lobi e nodi.

Questi orbitali esistono per livelli principali di n uguali a quattro o più. Quando gli orbitali si sovrappongono uno all'altro, emerge una forma approssimativamente sferica. Questo è il motivo per cui gli atomi sono generalmente rappresentati come sfere.

orbitali atomici

Un orbitale atomico rappresenta le regioni tridimensionali di un atomo in cui un elettrone ha la più alta probabilità di risiedere. La funzione di distribuzione radiale indica la probabilità totale di trovare un elettrone all'interno del guscio sottile ad una distanza r dal nucleo. Gli orbitali atomici hanno forme distinte determinate da l, il numero quantico del momento angolare. Gli orbitali sono spesso disegnati con una superficie di confine, che racchiude le regioni più dense della nuvola.

Il numero quantico del momento angolare è un numero intero che può assumere i valori l = 0, 1, 2, …, n – 1. Un orbitale con un numero quantico principale pari a 1 (n = 1) può avere un solo valore di l ( l = 0), mentre un numero quantico principale pari a 2 (n = 2) consente l = 0 e l = 1. Orbitali con lo stesso valore di l definiscono una sottozona.

Gli orbitali con l = 0 sono chiamati orbitali s e costituiscono i sottogusci s. Il valore l = 1 corrisponde agli orbitali p. Per un dato n, gli orbitali p costituiscono una sottozona p (cioè 3p se n = 3). Gli orbitali con l = 2 sono chiamati orbitali d. Gli orbitali con l = 3, 4 e 5 sono gli orbitali f, g e h.

L'orbitale con l'energia più bassa è l'orbitale 1s. Questo è un orbitale sfericamente simmetrico. La densità di probabilità (ψ_2) di un orbitale 1s implica che è più probabile che l'elettrone si trovi nel nucleo. Tuttavia, date le forze elettrostatiche tra protoni ed elettroni, ciò non rappresenta accuratamente dove risiederà l’elettrone. Viene invece utilizzata la funzione di distribuzione radiale, che è un grafico della probabilità totale di trovare un elettrone in un orbitale con un dato raggio r. La funzione di distribuzione radiale si trova moltiplicando la densità di probabilità per il volume di gusci sferici sottili con raggi, r. Per l'orbitale 1s dell'idrogeno, la funzione di distribuzione radiale ha un valore zero al nucleo, che aumenta fino a un massimo a 52,9 picometri prima di diminuire all'aumentare di r.

Ci sono certe distanze dal nucleo alle quali la densità di probabilità di trovare un elettrone situato su un particolare orbitale è zero. In altre parole, il valore della funzione d'onda ψ è zero a questa distanza per questo orbitale. Un tale valore di r è chiamato nodo radiale. Il numero di nodi radiali in un orbitale è n – l – 1. Per gli orbitali 2s, dove n = 1, c'è un nodo radiale, mentre gli orbitali 3s hanno due nodi radiali.

Ogni livello principale con n = 2 o più contiene tre orbitali p. I tre orbitali p hanno due lobi con un nodo situato nel nucleo. L'orientamento degli orbitali p nello spazio è descritto dal valore di ml. I tre orbitali p sono reciprocamente perpendicolari (ortogonali) tra loro. Gli orbitali p più alti (3p, 4p, 5p e superiori) hanno forme simili ma sono di dimensioni maggiori con nodi radiali aggiuntivi.

I livelli principali con n = 3 o più contengono cinque orbitali d. Quattro di questi orbitali sono costituiti da una forma a quadrifoglio, con quattro lobi densi di elettroni. Ci sono due piani nodali perpendicolari che si intersecano nel nucleo. In questi piani nodali la densità elettronica è zero. Uno degli orbitali d ha una forma leggermente diversa e ha due lobi orientati sull'asse z con un anello a forma di ciambella sul piano xy. I livelli principali con n = 4 e superiori contengono sette orbitali f, che hanno forme complesse. Questi orbitali hanno più nodi e lobi degli orbitali d.

<img alt="Figure1" src="https://www.jove.com/files/core/CDNSource/lessons/983/983Image 1.png" style="width: 700px;" />

Figura 1: orbitali rappresentativi s, p, d e f.

Queste diverse forme degli orbitali atomici rappresentano le regioni tridimensionali all'interno delle quali è probabile che si trovi l'elettrone. Tutti gli orbitali insieme formano una forma approssimativamente sferica, motivo per cui gli atomi sono generalmente rappresentati come sfere.

Questo testo è adattato da <a href="https://openstax.org/books/chemistry-2e/pages/6-3-development-of-quantum-theory">Openstax, Chemistry 2e, Section 6.3: Development of Quantum Theory.</a>

Orbitali atomici

Un orbitale atomico rappresenta le regioni tridimensionali di un atomo in cui un elettrone ha la più alta probabilità di risiedere. La distribuzione 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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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 =...

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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.

Electron Regions in Atomic Orbitals | JoVE K12

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Electron Regions in Atomic Orbitals

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