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

تصف النظرية المدارية الجزيئية توزيع الإلكترونات في جميع أنحاء الجزيء بدلا من توطينها في روابط محددة بين الذرات.
يتوافق التداخل البناء بين المدارات الذرية في الطور مع زيادة كثافة الإلكترون بين النوى الموجبة الشحنة ، مما يجعل الجزيء أكثر استقرارا. هذا المدار الجزيئي الترابط أقل في الطاقة من أي من المدارات الذرية الأصلية.
يتوافق التداخل المدمر بين المدارات الذرية خارج الطور مع انخفاض كثافة الإلكترون في مستوى عقدي بين النوى ، مما يجعل الجزيء أقل استقرارا. هذا المدار الجزيئي المضاد للترابط أعلى في الطاقة من المدارات الذرية ويتميز بنجمة أو علامة النجمة.
تصنف المدارات الجزيئية حسب طريقة تداخل المدارات الذرية. ينتج عن الجمع وجها لوجه من المدارات الذرية على طول المحور بين النوى ، مثل التداخل بين مدارين s أو مدارين p من طرف إلى طرف ، مدارات جزيئية سيجما. تتركز كثافة الإلكترون المداري سيجما حول المحور بين النوى.
ينتج عن التداخل الجانبي ، مثل التداخل الجانبي لمدارين p ، مدارات جزيئية pi. هنا ، تتركز كثافة الإلكترون على جانبي المحور بين النوى.
يعني اتجاه المدارات p الثلاثة المختلفة أنه عادة ما يتداخل زوج واحد من طرف إلى طرف ويتداخل الزوجان الآخران بشكل جانبي. عادة ما تكون مدارات الترابط pi متساوية في الطاقة ، أو متدهورة ، وكذلك المدارات المضادة للترابط pi.
تتوقع نظرية المدار الجزيئي استقرار الروابط التساهمية من ترتيب رابطة الجزيء ، وهو عدد الإلكترونات في مدارات الترابط مطروحا منه عدد الإلكترونات في المدارات المضادة للترابط مقسوما على اثنين.
يشير ترتيب الرابطة الأكبر من الصفر إلى أنه يمكن أن توجد رابطة تساهمية واحدة أو أكثر ، في حين أن ترتيب الرابطة صفر يعني أنه لا ينبغي أن تكون الروابط موجودة.
النظرية المدارية الجزيئية مفيدة أيضا للجزيئات متعددة الذرات مثل البنزين. لا يمكن لنموذج لويس للبنزين تمثيل إلكتروناته غير المتمركزة بدقة ، في حين أن النظرية المدارية الجزيئية تخصص هذه الإلكترونات إلى ثلاثة مدارات جزيئية رابطة pi تغطي حلقة الكربون بأكملها.

هذا النص مقتبس من <a href = "https://openstax.org/books/chemistry-2e/pages/8-4-molecular-orbital-theory" >Openstax ، الكيمياء 2 ه ، القسم 8.4 النظرية المدارية الجزيئية</a>.

نظرية المدارات الجزيئية mo والترابط التساهمي

<div style="direction:rtl">تصف نظرية المدارات الجزيئية توزيع الإلكترونات في الجزيئات بطريقة مشابهة لتوزيع الإلكترونات في المدارات الذرية. تسمى منطقة الفضاء التي من المحتمل أن يوجد فيها إلكترون التكافؤ في الجزيء بالمدار الجزيئي. رياضياً، يؤدي الجمع الخطي للمدارات الذرية (LCAO) إلى توليد مدارات جزيئية. تؤدي مجموعات وظائف الموجة المدارية الذرية في الطور إلى مناطق ذات احتمالية عالية لكثافة الإلكترون، بينما تنتج الموجات خارج الطور عقدًا أو مناطق لا توجد بها كثافة إلكترون. يؤدي الجمع في الطور بين مدارين ذريين s على ذرات متجاورة إلى إنتاج مدار جزيئي σs منخفض الطاقة حيث تكون معظم كثافة الإلكترون مباشرة بين النوى. الجمع خارج الطور ينتج مدار جزيئي مضاد للترابط σs* ذي طاقة أعلى، حيث توجد عقدة بين النوى. وبالمثل، فإن الدالة الموجية للمدارات p تؤدي إلى فصين لهما طورين متقابلين. عندما تتداخل مدارات p من طرف إلى طرف، فإنها تكوّن σ وσ*. يؤدي التداخل جنبًا إلى جنب بين مدارين p إلى إنشاء مدارات جزيئية π و π* مضادة للترابط. يوضح الرسم التخطيطي المداري الجزيئي المملوء عدد الإلكترونات الموجودة في المدارات الجزيئية المترابطة والمضادة. يساهم الإلكترون في تفاعل الترابط فقط إذا كان يحتل مدار الترابط. يتم تحديد المساهمة الصافية للإلكترونات في قوة الرابطة للجزيء من ترتيب الرابطة، والذي يتم حسابه على النحو التالي: <img alt="Figure1" src="/files/ftp_upload/11687/11687%20PT%20equation%201.png" style="text-align: center; height: 40px;"> ترتيب الرابطة هو دليل على قوة الرابطة التساهمية؛ الرابطة بين ذرتين معينتين تصبح أقوى مع زيادة ترتيب الرابطة. إذا أدى توزيع الإلكترونات في المدارات الجزيئية إلى رتبة رابطة صفر، فلن تتشكل رابطة مستقرة. النظرية المدارية الجزيئية مفيدة أيضًا للجزيئات متعددة الذرات. لا يمكن لنموذج لويس للبنزين (C6H6), الذي يحتوي على بنية سداسية مستوية مع ذرات الكربون المهجنة sp2، أن يمثل بدقة إلكتروناته غير المتمركزة. ومع ذلك، فإن النظرية المدارية الجزيئية تحدد تلك الإلكترونات إلى ثلاثة مدارات جزيئية مرتبطة بـ π تغطي حلقة الكربون بأكملها. وينتج عن ذلك مجموعة مشغولة بالكامل (6 إلكترونات) من المدارات الجزيئية المترابطة التي تمنح حلقة البنزين استقرارًا ديناميكيًا حراريًا وكيميائيًا إضافيًا.</div>

نظرية المدارات الجزيئية MO والترابط التساهمي

تصف النظرية المدارية الجزيئية توزيع الإلكترونات في الجزيئات بطريقة مشابهة لتوزيع الإلكترونات في المدارات الذرية. ...

Education

JoVE Core

Organic Chemistry

الكيمياء العضوية

Unit 1

الوحدة الأولى

Covalent Bonding and Structure

الترابط التساهمي والبنية

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

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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9C.3.2.1.3

4 Communicating reasons, arguments and ideas to others
 4.2 Obtaining, evaluating and communicating information
  4.2.1 Students will be able to read and interpret multiple sources to obtain information, evaluate the merit and validity of claims and design solutions, and communicate information, ideas, and evidence in a variety of formats.

Bond Order and Molecular Orbitals

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