Name: bond order and molecular orbitals
Uploaded: 2023-04-30T18:28:31.000Z
Duration: 2 min 40 s
Channel: JoVE

K12 Standards

Minnesota Academic Standards in Science

9-12

Chemistry

4.2.1 9C.3.2.1.2

MO Theory and Covalent Bonding

Moleküler orbital teori, elektronları atomlar arasındaki belirli bağlara lokalize etmek yerine bir molekül boyunca dağılımını tanımlar.
Faz içi atomik orbitaller arasındaki yapıcı girişim, pozitif yüklü çekirdekler arasındaki daha büyük elektron yoğunluğuna karşılık gelir ve molekülü daha kararlı hale getirir. Bu bağ moleküler orbitali, orijinal atomik orbitallerin herhangi birinden daha düşük enerjiye sahiptir.
Faz dışı atomik orbitaller arasındaki yıkıcı girişim, çekirdekler arasındaki bir düğüm düzleminde daha düşük elektron yoğunluğuna karşılık gelir ve molekülü daha az kararlı hale getirir. Bu bağlanma önleyici moleküler orbital, enerji bakımından atomik orbitallerden daha yüksektir ve bir yıldız veya yıldız işareti ile işaretlenmiştir.
Moleküler orbitaller, atomik orbitallerin örtüşme şekline göre sınıflandırılır. İki s orbitali veya iki uçtan uca p orbitali arasındaki örtüşme gibi, çekirdekler arası eksen boyunca atomik orbitallerin kafa kafaya kombinasyonu, sigma moleküler orbitallerle sonuçlanır. Sigma orbital elektron yoğunluğu, çekirdekler arası eksen etrafında merkezlenmiştir.
İki p orbitalinin yandan örtüşmesi gibi yanlara doğru örtüşme, pi moleküler orbitalleri ile sonuçlanır. Burada elektron yoğunluğu, çekirdekler arası eksenin zıt taraflarında yoğunlaşmıştır.
Üç farklı p orbitalinin oryantasyonu, tipik olarak bir çiftin uçtan uca örtüştüğü ve diğer iki çiftin yanlara doğru örtüştüğü anlamına gelir. Pi bağ orbitalleri tipik olarak enerji bakımından eşittir veya pi antibonding orbitalleri gibi dejenere olur.
Moleküler orbital teori, molekülün bağ sırasından, bağ orbitallerindeki elektron sayısı eksi antibağ orbitallerindeki elektron sayısının ikiye bölünmesi olan kovalent bağların kararlılığını tahmin eder.
Sıfırdan büyük bir bağ sırası, bir veya daha fazla kovalent bağın var olabileceğini gösterirken, sıfır olan bir bağ sırası, bağların olmaması gerektiği anlamına gelir.
Moleküler orbital teori, benzen gibi çok atomlu moleküller için de yararlıdır. Lewis benzen modeli, delokalize elektronlarını doğru bir şekilde temsil edemezken, moleküler orbital teorisi bu elektronları tüm karbon halkasını kaplayan üç pi bağı moleküler orbitaline atar.

Bu metin <a href="https://openstax.org/books/chemistry-2e/pages/8-4-molecular-orbital-theory">Openstax, Chemistry 2e, Section 8.4 Molecular Orbital Theory adlı kitaptan uyarlanmıştır</a>.

mo teorisi ve kovalent bağlar

Moleküler yörünge teorisi, elektronların moleküllerdeki dağılımını, atomik yörüngelerdeki elektronların dağılımına benzer şekilde açıklar. Bir moleküldeki değerlik elektronunun bulunma ihtimalinin bulunduğu uzay bölgesine moleküler yörünge denir. Matematiksel olarak atomik yörüngelerin (LCAO) doğrusal birleşimi moleküler yörüngeler üretir. Faz içi atomik yörünge dalga fonksiyonlarının kombinasyonları, elektron yoğunluğu olasılığı yüksek olan bölgelerle sonuçlanırken, faz dışı dalgalar, elektron yoğunluğu olmayan düğümler veya bölgeler üretir.

Bitişik atomlardaki iki atomik yörüngenin aynı fazda birleşimi, elektron yoğunluğunun çoğunun doğrudan çekirdekler arasında olduğu daha düşük enerjili bir σs bağlayıcı moleküler yörünge üretir. Faz dışı ekleme, çekirdekler arasında bir düğümün bulunduğu, daha yüksek enerjili bir σs* antibağ moleküler yörüngesi üretir.

Benzer şekilde, p-orbitallerinin dalga fonksiyonu zıt fazlı iki lobun ortaya çıkmasına neden olur. p-orbitalleri uç uca örtüştüğünde σ ve σ* yörüngeleri oluşur. İki p yörüngesinin yan yana örtüşmesi, π bağı ve π* antibağ moleküler yörüngelerini oluşturur.

Dolu moleküler yörünge diyagramı, bağ ve antibağ moleküler yörüngelerindeki elektronların sayısını gösterir. Bir elektron yalnızca bir bağlanma yörüngesini işgal ederse bağlanma etkileşimine katkıda bulunur. Elektronların bir molekülün bağ kuvvetine net katkısı, aşağıdaki şekilde hesaplanan bağ sırasına göre belirlenir:

<img alt="Figure1" src="/files/ftp_upload/11687/11687%20PT%20equation%201.png" style="text-align: center; height: 40px;">

Bağ sırası, kovalent bir bağın kuvvetine ilişkin bir kılavuzdur; Belirli iki atom arasındaki bağ, bağ sırası arttıkça güçlenir. Moleküler yörüngelerdeki elektronların dağılımı sıfır bağ derecesi veriyorsa, kararlı bir bağ oluşmaz.

Moleküler yörünge teorisi aynı zamanda çok atomlu moleküller için de faydalıdır. sp2 hibritlenmiş karbon atomları ile düzlemsel altıgen bir yapıya sahip olan benzenin (C6H6) Lewis modeli, lokalize olmayan elektronlarını doğru bir şekilde temsil edemez. Bununla birlikte, moleküler yörünge teorisi, bu elektronları, tüm karbon halkasını kaplayan üç π bağlayıcı moleküler yörüngeye atar. Bu, benzen halkasına ek termodinamik ve kimyasal stabilite kazandıran, tamamen dolu (6 elektron) bir dizi bağlanma moleküler yörüngesiyle sonuçlanır.

MO Teorisi ve Kovalent Bağlar

Moleküler orbital teorisi, elektronların moleküllerdeki dağılımını, atomik orbitallerdeki elektronların dağılımına benzer bir şekilde tanımlar. ...

Education

JoVE Core

Organic Chemistry

Organik Kimya

Unit 1

Ünite 1

Covalent Bonding and Structure

Kovalent Bağlanma ve Yapı

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

bond order and molecular orbitals

Molecular orbital theory explains how electrons are arranged in molecules. It treats electron regions in a molecule much like atomic orbitals in an atom. A molecular orbital is the region of space where a valence electron is most likely to be found.

Molecular orbitals form through the linear combination of atomic orbitals, or LCAO. When atomic wave functions combine in phase, they create regions with high electron density. When they combine out of phase, they create nodes, or regions with no electron density.

Two adjacent s orbitals can overlap to form a lower-energy sigma s bonding molecular orbital. In this orbital, most of the electron density lies between the nuclei. The out-of-phase combination forms a higher-energy sigma s* antibonding molecular orbital, which has a node between the nuclei.

p orbitals also build molecular orbitals. Their wave functions have two lobes with opposite phases. End-to-end overlap of p orbitals produces sigma and sigma* orbitals, while side-by-side overlap produces pi bonding and pi* antibonding molecular orbitals.

A filled molecular orbital diagram shows how many electrons occupy bonding and antibonding orbitals. An electron adds to bond strength only when it is in a bonding orbital. The overall effect is measured by bond order, which helps show how strong a covalent bond is.

As bond order increases, the bond between two atoms becomes stronger. If the molecular orbital arrangement gives a bond order of zero, a stable bond does not form. Molecular orbital theory also helps explain polyatomic molecules. In benzene, the Lewis model cannot show the delocalized electrons in its planar hexagonal ring of sp2 hybridized carbon atoms. Molecular orbital theory places those electrons in three pi bonding molecular orbitals spread across the whole ring. With 6 electrons filling these bonding orbitals, benzene gains extra thermodynamic and chemical stability.

Bond Order and Molecular Orbitals

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chemical bonds

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polar covalent bonds

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Bond Order and Molecular Orbitals | JoVE K12

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9C.3.2.1.3

4 Communicating reasons, arguments and ideas to others
 4.2 Obtaining, evaluating and communicating information
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Bond Order and Molecular Orbitals

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