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

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Atomic Orbitals

A região mais densa da nuvem de elétrons onde é mais provável que se encontre um elétron é descrito em termos de orbitais atômicos. A forma de um orbital atômico é determinada pelo número quântico de impulso angular, l. Recorde-se que os valores de l são baseados no número de quantum principal, n os valores possíveis de l variam entre zero e n menos um.Quando n é maior do que um, existem múltiplos subníveis. Cada valor de l corresponde ou a um s, p, d, ou f orbital. O orbital de menor energia é o orbital 1-s.Este é um orbital esférico simétrico. A densidade de probabilidade de um orbital de 1-s revela que o elétron é mais provável de ser encontrado no núcleo. No entanto, dadas as forças eletrostáticas entre protões e elétrons isto não é provável.Multiplicando a densidade da probabilidade pelo volume das camadas esféricas finas com raios r esta é mais representativa. A probabilidade total de encontrar um elétron dentro da camada fina a uma distância r do núcleo é a função de distribuição radial. Para o hidrogénio, a maior probabilidade de encontrar um elétron está a 52, 9 picometros a partir do núcleo.Assim, a forma do orbital atômico 1-s para o hidrogénio é esférico com um raio de 52, 9 picometros. As orbitais de dois e três também são esféricas. São maiores e têm nós.Num nódulo, a probabilidade de encontrar um elétron é zero. Os principais níveis com n igual a dois ou mais também contêm três p-orbitais. Estes são em forma de lóbulo com um nó no núcleo.A sua orientação é descrita pelo valor de m-l. Os três p-orbitais são ortogonais um para o outro. Os principais níveis de n igual a três ou mais também têm cinco d orbitais.As orbitais com a forma de trevo têm quatro lóbulos densos de elétrons e dois planos nodais perpendiculares. Um dos d-orbitais é ligeiramente diferente. Os f orbitais têm mais lóbulos e nós.Estes orbitais existem para os níveis principais de n iguais a quatro ou mais. Quando os orbitais se sobrepõem uns aos outros, emerge uma forma aproximadamente esférica. É por isso que os átomos são geralmente representados como esferas.

orbitais atómicas

Uma orbital atómica representa as regiões tridimensionais de um átomo onde um eletrão tem a maior probabilidade de residir. A função de distribuição radial indica a probabilidade total de encontrar um eletrão dentro da fina camada a uma distância r do núcleo. As orbitais atómicas têm formas distintas que são determinadas por l, o número quântico do momentum angular. As orbitais são frequentemente desenhadas com uma superfície de limite, envolvendo as regiões mais densas da nuvem. 

O número quântico do momentum angular é um número inteiro que pode ter os valores, l = 0, 1, 2, …, n – 1. Uma orbital com um número quântico principal de 1 (n = 1) pode ter apenas um valor de l (l = 0), enquanto que um número quântico principal de 2 (n = 2) permite l = 0 e l = 1. Orbitais com o mesmo valor de l definem uma subcamada.

As orbitais com l = 0 são chamadas orbitais s e formam as subcamadas s. O valor l = 1 corresponde às orbitais p. Para um determinado n, as orbitais p constituem uma subcamada p (isto é, 3p se n = 3). As orbitais com l = 2 são chamadas de orbitais d. As orbitais com l = 3, 4, e 5 são as orbitais f, g, e h. 

A orbital de menor energia é a orbital 1s. Trata-se de uma orbital esfericamente simétrica. A densidade de probabilidade (ψ2) de uma orbital 1s implica que é mais provável encontrar o eletrão no núcleo. No entanto, dadas as forças eletrostáticas entre protões e eletrões, isto não representa com precisão o local onde o eletrão reside. Em vez disso, é utilizada a Função de Distribuição Radial,  que é um gráfico da probabilidade total de encontrar um eletrão em uma orbital em um determinado raio r. A função de distribuição radial é encontrada multiplicando a densidade de probabilidade pelo volume de camadas esféricas finas com raios, r. Para a orbital 1s do hidrogénio, a Função de Distribuição Radial tem um valor de zero no núcleo, que aumenta até ao máximo de 52,9 picómetros antes de diminuir com o aumento do r.

Existem algumas distâncias do núcleo em que a densidade de probabilidade de encontrar um eletrão localizado em uma orbital específica é zero. Por outras palavras, o valor da função de onda ψ é zero a essa distância para essa orbital. Esse valor de r é chamado de nó radial. O número de nós radiais em uma orbital é n – l – 1. Para orbitais 2s, onde n = 1, há um nó radial, enquanto que orbitais 3s têm dois nós radiais. 

Cada nível principal com n = 2 ou mais contém três orbitais p. As três orbitais p têm dois lóbulos com um nó localizado no núcleo. A orientação das orbitais p no espaço é descrita pelo valor de ml. As três orbitais p são mutuamente perpendiculares (ortogonais) entre si. As orbitais p superiores (3p, 4p, 5p, e superiores) têm formas semelhantes, mas são maiores em tamanho com nós radiais adicionais.

Níveis principais com n = 3 ou mais contêm cinco orbitais d. Quatro dessas orbitais consistem em uma forma de folha de trevo, com quatro lóbulos densos em eletrões. Existem dois planos de nós perpendiculares que se cruzam no núcleo. Nesses planos de nós, a densidade de eletrões é zero. Uma das orbitais d é ligeiramente diferente na forma e tem dois lóbulos orientados no eixo z com um anel em forma de donut no plano xy. Níveis principais com n = 4 e superior contêm sete orbitais f, que têm formas complexas. Estas orbitais têm mais nós e lóbulos do que as orbitais d.

<img alt="Figure1" src="https://www.jove.com/files/core/CDNSource/lessons/983/983Image 1.png" style="width: 700px;" />

Figura 1: Orbitais s, p, d e f representativas.

Estas diferentes formas das orbitais atómicas representam as regiões tridimensionais dentro das quais é provável que o eletrão seja encontrado. Todas as orbitais juntas formam uma forma aproximadamente esférica, e é por isso que os átomos são geralmente representados como esferas.

Este texto é adaptado de <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>

Orbitais Atómicas

Um orbital atômico representa as regiões tridimensionais em um átomo onde um elétron tem a maior probabilidade de residir. A distribuição radial ...

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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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