Name: electron filling order in atomic orbitals
Uploaded: 2020-09-03T13:38:28.000Z
Duration: 3 min 2 s
Channel: JoVE

K12 Standards

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NC K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.1.3

The Aufbau Principle and Hund's Rule

Occorre ricordare che gli orbitali atomici hanno energie diverse e possono ospitare due elettroni ciascuno. Il principio aufbau determina la distribuzione degli elettroni fra i subshell dell'atomo e la regola della massima molteplicità di Hund, spiega, inoltre, il riempimento degli orbitali nei subshell. Il principio aufbau afferma che nello stato fondamentale, gli elettroni riempiono gli orbitali atomici dall'energia più bassa a quella più elevata per ottenere la configurazione a minor energia.

Sebbene l'energia generalmente aumenti con il numero di gusci, la maggiore penetrazione degli orbitali s spesso porta gli orbitali quattro-s e cinque-s ad avere energie inferiori, rispettivamente, degli orbitali tre-d e quattro-d. L'ordine può essere ricordato utilizzando diagrammi come questo, dove il percorso della freccia rivela la sequenza in cui gli elettroni sono assegnati agli orbitali. Si consideri la possibilità di scrivere la configurazione elettronica per il carbonio, un elemento con numero atomico sei.

Certamente, l'orbitale uno, che ha l'energia più bassa, dovrebbe essere riempito prima dell'orbitale due-s. Ogni orbitale può contenere un massimo di due elettroni. Il quinto elettrone entra in un subshell due-p.

Ma quale dei tre orbitali due-p occupa? Dunque! Si presume che gli orbitali in qualsiasi subshell siano degenerati, il che significa che hanno la stessa energia.

Pertanto, il quinto elettrone può entrare in uno qualsiasi dei tre orbitali due-p. E il sesto elettrone? Entra nell'orbitale due-p con un elettrone o uno degli orbitali due-p vuoti?

Secondo la regola della massima molteplicità di Hund, gli elettroni occupano singolarmente tutti gli orbitali di un dato livello di energia prima di iniziare l'appaiamento, e gli elettroni spaiati non possono avere spin opposti:i loro spin devono essere paralleli. Dunque, per il carbonio, i 2 elettroni due-p devono occupare due orbitali diversi e avere spin paralleli. In questo modo, gli elettroni possono diffondersi su un'area più ampia.

Ciò diminuisce la schermatura reciproca, riducendo così al minimo l'energia dell'atomo. Per l'azoto, ciascuno dei tre orbitali due-p è occupato singolarmente. Per l'ossigeno, una volta che gli orbitali degenerati due-p sono riempiti singolarmente, l'ultimo elettrone deve accoppiarsi con un altro elettrone due-p.

L'atomo ha due elettroni spaiati. La configurazione elettronica del neon rivela che il guscio più esterno è riempito alla capacità massima di otto elettroni. Il neon ha due elettroni, detti elettroni del nucleo nel guscio interno, e otto elettroni, detti elettroni di valenza, nel guscio più esterno.

il principio di aufbau e la regola di hund

Per determinare la configurazione elettronica di un particolare atomo, possiamo costruire le strutture nell'ordine dei numeri atomici. Cominciando dall'idrogeno e continuando attraverso i periodi della tavola periodica, aggiungiamo un protone alla volta al nucleo e un elettrone al sottolivello appropriato finch non avremo descritto le configurazioni elettroniche di tutti gli elementi. Questo procedimento chiamato principio Aufbau, dalla parola tedesca aufbau (“costruire?). Ogni elettrone aggiunto occupa il sottolivello di energia pi bassa disponibile, soggetto alle limitazioni imposte dai numeri quantici consentiti secondo il principio di esclusione di Pauli. Gli elettroni entrano nei subshell ad alta energia solo dopo che i subshell a energia inferiore sono stati riempiti al massimo della loro capacit. La Figura 1 illustra il modo tradizionale di ricordare l'ordine di riempimento degli orbitali atomici.

<img alt="Figure1" src="https://www.jove.com/files/core/CDNSource/lessons/986/986Image_1.png" style="width: 700px;" />

Figura 1 Questo diagramma illustra l'ordine energetico per gli orbitali atomici ed utile per derivare configurazioni elettroniche dello stato fondamentale.

Considera l'idea di scrivere la configurazione elettronica del carbonio, un elemento con numero atomico sei. Quattro elettroni riempiono gli orbitali 1 e 2. I restanti due elettroni occupano il sottolivello 2p. Ora possiamo scegliere se riempire uno degli orbitali 2p e accoppiare gli elettroni o lasciarli spaiati in due orbitali p diversi, ma degenerati. Gli orbitali sono riempiti come descritto dalla regola di Hund: la configurazione a energia pi bassa per un atomo con elettroni all'interno di un insieme di orbitali degeneri quella avente il numero massimo di elettroni spaiati. Pertanto, i due elettroni negli orbitali del carbonio 2p hanno numeri quantici n, l e ms identici e differiscono nel loro numero quantico ml (in accordo con il principio di esclusione di Pauli). Il diagramma orbitale del carbonio, con una configurazione elettronica di 1s22s21p2 :

<img alt="Figure2" src="https://www.jove.com/files/core/CDNSource/lessons/986/986Image_2.png" style="width: 300px;" />

L’azoto (numero atomico 7) riempie i subshell 1s e 2s e ha un elettrone in ciascuno dei tre orbitali 2p, secondo la regola di Hund. Questi tre elettroni hanno spin spaiati. L'ossigeno (numero atomico 8) ha una coppia di elettroni in uno qualsiasi degli orbitali 2p (gli elettroni hanno spin opposti) e un singolo elettrone in ciascuno degli altri due. Il fluoro (numero atomico 9) ha solo un orbitale 2p contenente un elettrone spaiato. Tutti gli elettroni nel gas nobile neon (numero atomico 10) sono accoppiati e tutti gli orbitali nei gusci n = 1 e n = 2 sono pieni.

Questo testo adattato da <a href="https://openstax.org/books/chemistry-2e/pages/6-4-electronic-structure-of-atoms-electron-configurations">Openstax, Chemistry 2e, Section 6.4: Electronic Structure of Atoms.</a>

Il principio di Aufbau e la regola di Hund

Per determinare la configurazione elettronica di un particolare atomo, possiamo costruire le strutture nell'ordine dei numeri atomici. A cominciare dall'idrogeno, e ...

Education

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Chimica

Electronic Structure of Atoms

Struttura elettronica degli atomi

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

electron filling order in atomic orbitals

Electron filling order in atomic orbitals follows the aufbau principle and Hund's rule. To write an electron configuration, we build atoms in order of atomic number. Starting with hydrogen and moving across the periods of the periodic table, one proton is added to the nucleus and one electron is placed into the correct subshell. This process describes the ground-state electron configurations of the elements.

The aufbau principle comes from the German word aufbau, which means &quot;to build up.&quot; It says that each added electron enters the lowest-energy subshell available. The Pauli exclusion principle still applies, so electrons must follow the allowed quantum numbers. Higher-energy subshells do not fill until lower-energy subshells reach capacity.

A common filling-order diagram helps show the energy sequence of the atomic orbitals. Carbon is a useful example because it has atomic number 6. Four electrons fill the 1s and 2s orbitals, and the remaining two electrons go into the 2p subshell. At that point, the electrons can either pair in one 2p orbital or stay unpaired in two different p orbitals.

Hund's rule gives the lower-energy choice for degenerate orbitals, which are orbitals with the same energy. The rule states that electrons in a set of degenerate orbitals occupy the arrangement with the maximum number of unpaired electrons. In carbon, the two 2p electrons have the same n, l, and m_s quantum numbers, and they differ in m_l, which matches the Pauli exclusion principle.

Nitrogen, with atomic number 7, fills the 1s and 2s subshells and places one electron in each of the three 2p orbitals. These three electrons are unpaired. Oxygen, atomic number 8, has one pair of electrons in one 2p orbital and one single electron in each of the other two. Fluorine, atomic number 9, has only one 2p orbital with an unpaired electron.

Neon, atomic number 10, has all paired electrons. Its n = 1 and n = 2 shells are completely filled. This pattern shows how electron configurations build step by step across the first ten elements.

Electron Filling Order in Atomic Orbitals

electron-filling-order-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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the aufbau principle and hund's rule

Electron filling order in atomic orbitals follows the aufbau principle and Hund's rule. To write an electron configuration, we build atoms in order of atomic number. Starting with hydrogen and moving across the periods of the periodic table, one proton is added to the nucleus and one electron is placed into the correct subshell. This process describes the ground-state electron configurations of the elements. The aufbau principle comes from the German word aufbau, which means "to build up." It...

electron configuration of multielectron atoms

electron-configuration-of-multielectron-atoms

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Valence electrons and noble gas shorthand help show how electrons are arranged in multielectron atoms. Sodium, the alkali metal with atomic number 11, has one more electron than neon. That extra electron goes into the lowest-energy subshell available, the 3s orbital, so sodium has the configuration 1s2 2s2 2p6 3s1. Electrons in the outermost shell, where n is highest, are called valence electrons. Electrons in the inner shells are called core electrons. Because core electrons often match a...

key terms and concepts

Learn how electron configurations build by atomic number, why lower-energy orbitals fill first, and how Hund's rule shapes carbon, nitrogen, oxygen, fluorine, and neon.

Electron Filling Order in Atomic Orbitals | JoVE K12

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Matter And Its Interactions

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New York State Science Learning Standards

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Electron Filling Order in Atomic Orbitals

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