Name: shielding and orbital penetration
Uploaded: 2020-09-03T13:38:28.000Z
Duration: 3 min 21 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry and Physics

IPC.7

IPC.7.E

The Energies of Atomic Orbitals

Atomik orbitaller, Coulomb etkileşimleri, kalkanlama etkisi ve orbital penetrasyonuyla açıklanan farklı enerjilere sahiptir. Coulomb yasası, iki yüklü parçacık arasındaki çekici veya itici kuvvetin, aralarındaki mesafenin karesi ile ters orantıya sahip olduğunu belirtir. Atomik orbital boyutları, kabuk sayısı ile artar ve elektronlar, alt kabuk orbitallerinin kapladığı alandan itilir.Bu nedenle, Coulomb yasası, kabuk sayısı arttıkça elektronların çekirdeğe daha az çekim duyduğunu, bunun da daha yüksek orbital enerjilerine karşılık geldiğini ileri sürer. Ek olarak, çekirdekten yaklaşık olarak aynı uzaklıkta veya ona daha yakın olan elektronlar, çekirdeğe olan çekiciliği daha da azaltan bir perdeleme etkisine sahiptir. Perdeleme etkisi ne kadar büyükse, çekirdeğe o kadar az ilgi hissedilir.Bu, elektron kabukları içindeki orbital enerjilerindeki farklılıkların bir nedenidir. Örneğin, 3s ve 3p elektronları 3d elektronları önemli ölçüde perdeler. Bir elektronun hissettiği etkin nükleer yük, perdeleyici elektronların sayısına ve işgal ettikleri alt kabukların sayısına bağlı olan perdeleme sabiti S'nin atom numarasından çıkarılmasıyla hesaplanır.Örneğin atom numarası 3 olan lityumdaki iki 1s elektronu, 2s elektronunu tarar. Bu elektron için perdeleme sabiti yarı ampirik kurallardan 1, 7 olarak belirlenir. Dolayısıyla, 2s elektronunun hissettiği etkin nükleer yük 1, 3'tür.Orbitallerin şekilleri de enerjilerini belirler. Eğer bir dış orbitaldeki elektronlar, çekirdeğe yakın olmak için iç elektronların işgal ettiği alanlara gidebilirlerse, orada çok daha az perdelenmiş olurlar. Böylece, o dış orbitalin enerjisi daha düşüktür.Bu, çekirdekten belirli bir mesafede bir elektron bulma olasılığını tanımlayan bir radyal dağılım fonksiyonu ile görselleştirilebilir. 1s, 2s ve 2p alt kabuklarının radyal dağılım fonksiyonu grafikleri, 2s elektronlarının çekirdeğe yakın olma olasılığı ortalama iken, 2p elektronlarının çoğunlukla 1s bölgesinin dışında veya dış kenarında kaldığını ortaya koymaktadır. Bu nedenle 2s orbitalinin daha fazla penetrasyon kabiliyetine sahip olduğu söylenir.Üçüncü kabukta, 3s elektronları en çok ve 3d elektronlar en az penetrandır. Genel olarak, atomik orbital enerjisi kabuk sayısı ile ve alt kabuk seviyesinde s'den f'ye yükselir. Bununla birlikte, dördüncü ve beşinci kabuklarda penetrasyon etkisi o kadar önemli hale gelir ki, 4s ve 5s orbitalleri genellikle sırasıyla 3d ve 4d orbitallerinden daha düşük bağıl enerjilere sahiptir.

atomik orbitallerin enerjileri

Bir atomda, negatif yüklü elektronlar, pozitif yüklü çekirdeğe çekilir. Bir multielektron atomunda, elektron-elektron itmeleri de gözlenir. Çekici ve itici kuvvetler, parçacıklar arasındaki mesafenin yanı sıra ayrı parçacıklar üzerindeki yüklerin işareti ve büyüklüğüne bağlıdır. Parçacıkların üzerindeki yükler zıt olduğunda birbirlerini çekerler. Her iki parçacık da aynı yüke sahipse, birbirlerini iterler.
 
 Yüklerin büyüklüğü arttıkça kuvvetin büyüklüğü de artar. Ancak yüklerin ayrışması fazla olduğunda kuvvetler azalır. Bu nedenle, bir elektron ile çekirdeği arasındaki çekim kuvveti, aralarındaki mesafeyle doğru orantılıdır. Elektron çekirdeğe daha yakınsa çekirdeğe daha sıkı bağlanır; bu nedenle, farklı kabuklardaki (farklı mesafelerde) elektronların farklı enerjileri vardır.
 
 Birden fazla enerji seviyesine sahip atomlar için, iç elektronlar, elektron-elektron itmeleri nedeniyle dış elektronları çekirdeğin çekmesinden kısmen korur. Çekirdek elektronlar elektronları dış kabuklarda korurken, aynı değerlik kabuğundaki elektronlar birbirlerinin deneyimlediği nükleer çekimi etkili bir şekilde engellemez. Bu, etkin nükleer yük kavramı Zeff ile açıklanabilir. Bu, herhangi bir elektron-elektron itmesi hesaba katılarak çekirdeğin belirli bir elektrona uyguladığı çekmedir. Hidrojen için yalnızca bir elektron vardır ve bu nedenle nükleer yük (Z) ve etkin nükleer yük (Zeff) eşittir. Diğer tüm atomlar için, iç elektronlar, dış elektronları çekirdeğin çekmesinden kısmen korur ve böylece:
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/985/985_Equations-01.png" style="height: 40px;" />
 
 Orbital penetrasyonu, bir elektronun çekirdeğe daha yakın olma yeteneğini tanımlar. s-orbitalindeki elektronlar çekirdeğe yaklaşabilir ve daha fazla penetrasyon etme kabiliyetine sahip olabilirler. Küresel bir s-orbital için olasılık yoğunluğu çekirdekte sıfır değildir.  Farklı alt kabukların farklı uzamsal yönelimleri vardır. Dambıl şeklindeki yörünge nedeniyle, p-elektron çok daha az penetre eder. Dalga işlevi, elektron bulma olasılığının sıfır olduğu çekirdekten geçen bir düğüme sahiptir. Böylece, s orbital elektronu çekirdeğe daha sıkı bağlanır ve p-elektrondan daha düşük enerjiye sahiptir. Bir d-elektron, p orbital elektrondan daha düşük penetrasyona ve daha yüksek enerjiye sahiptir. 
 
 Çeşitli kabuklar ve alt kabuklar için, bir elektronun penetrasyon gücü eğilimi aşağıdaki gibi gösterilebilir
 
 <img alt="Eq2" src="https://www.jovecore.com/CDNSource/lessons/985/985_Equations-02.png" style="height: 40px;" />
 
 Koruma ve penetrasyonun etkisi büyüktür ve 4s elektronu 3d elektrondan daha düşük enerjiye sahip olabilir.
 
 Bu metin bu kaynaktan uyarlanmıştır: <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 (Electron Configurations).</a>

Atomik Orbitallerin Enerjileri

Bir atomda, negatif yüklü elektronlar pozitif yüklü çekirdeğe çekilir. Çok elektronlu bir atomda, elektron-elektron itmeleri ...

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Electronic Structure of Atoms

Atomların Elektronik Yapısı

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

shielding and orbital penetration

Shielding and orbital penetration help explain why electrons in an atom have different energies. Electrons are attracted to the positive nucleus, but they also repel one another in atoms with more than one electron. The strength of these forces depends on the charge and the distance between the particles. Opposite charges attract, like charges repel, and the force gets weaker as the particles move farther apart.

An electron that stays closer to the nucleus is held more tightly. That means electrons in different shells can have different energies because they sit at different distances from the nucleus. In atoms with several energy levels, inner electrons partly block the nucleus from outer electrons. This blocking is called shielding, and it happens because of electron-electron repulsions.

The pull felt by one electron after shielding is the effective nuclear charge, or Zeff. It describes the attraction from the nucleus after repulsions are taken into account. For hydrogen, which has only one electron, Z and Zeff are the same. In atoms with more than one electron, core electrons shield outer electrons, while electrons in the same valence shell do not block the nuclear pull very well.

Orbital penetration describes how close an electron can get to the nucleus. s orbitals penetrate best because their spherical probability density is non-zero at the nucleus. p orbitals penetrate less because their dumbbell shape has a node through the nucleus, where the chance of finding an electron is zero. d orbitals penetrate even less than p orbitals.

Because of shielding and penetration, s electrons are usually bound more tightly and have lower energy than p electrons. d electrons have higher energy than p electrons. These effects can be strong enough that a 4s electron may have lower energy than a 3d electron.

Shielding and Orbital Penetration

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Shielding and orbital penetration help explain why electrons in an atom have different energies. Electrons are attracted to the positive nucleus, but they also repel one another in atoms with more than one electron. The strength of these forces depends on the charge and the distance between the particles. Opposite charges attract, like charges repel, and the force gets weaker as the particles move farther apart. An electron that stays closer to the nucleus is held more tightly. That means...

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key terms and concepts

Learn how shielding, effective nuclear charge, and orbital penetration affect electron energy levels, and why s, p, and d orbitals differ in energy.

Shielding and Orbital Penetration | JoVE K12

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Shielding and Orbital Penetration

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