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

分子軌道理論は、電子を原子間の特定の結合に局在させるのではなく、分子全体の電子の分布を説明しています。
同相原子軌道間の建設的な干渉は、正に帯電した原子核間の電子密度が高いことに対応し、分子をより安定させます。この結合分子軌道は、元の原子軌道のいずれよりもエネルギーが低くなります。
位相がずれた原子軌道間の破壊的な干渉は、原子核間の節面の電子密度の低下に対応し、分子の安定性を低下させます。この反結合性分子軌道は、原子軌道よりもエネルギーが高く、星またはアスタリスクでマークされています。
分子軌道は、原子軌道が重なり合う方法によって分類されます。2つのs軌道または2つの端から端までのp軌道間の重なりなど、核間軸に沿った原子軌道の正面からの組み合わせは、シグマ分子軌道になります。シグマ軌道の電子密度は、核間軸を中心にしています。
2つのp軌道の横方向の重なりなど、横方向の重なりは、π分子軌道になります。ここでは、電子密度は核間軸の反対側に集中しています。
3つの異なるp軌道の向きは、通常、1つのペアが端から端まで重なり、他の2つのペアが横に重なることを意味します。π結合性軌道は、通常、π反結合性軌道と同様に、エネルギーが等しいか縮退します。
分子軌道理論では、分子の結合順序から共有結合の安定性を予測します。これは、結合性軌道の電子数から反結合性軌道の電子数を引いた数を2で割ったものです。
結合次数が 0 より大きい場合は、1 つ以上の共有結合が存在することを示し、結合次数が 0 の場合は、結合が存在しないことを意味します。
分子軌道理論は、ベンゼンのような多原子分子にも有用です。ベンゼンのルイスモデルは、その非局在化電子を正確に表すことができませんが、分子軌道理論では、これらの電子を炭素環全体をカバーする3つのπ結合分子軌道に割り当てます。

このテキストは<a href="https://openstax.org/books/chemistry-2e/pages/8-4-molecular-orbital-theory">Openstax, Chemistry 2e, Section 8.4 Molecular Orbital Theoryから改作</a>されています。

mo理論と共有結合

分子軌道理論は、原子軌道内の電子の分布と同様の方法で分子内の電子の分布を説明します。 分子内の価電子が存在している空間領域の事を分子軌道と呼びます。 数学的には、原子軌道の線形結合 (LCAO) によって分子軌道を求められます。 同相の原子軌道波動関数の組み合わせでは、電子密度の確率が高い領域が生成されますが、位相がずれた原子軌道波動関数は電子密度のないノードまたは領域を生成します。
隣接する2 つの原子の s 軌道の同相結合により、電子密度の大部分が原子核間に直接存在する、より低いエネルギーの σ s 結合分子軌道が生成されます。 位相ずれの付加により、より高いエネルギーの σs* 反結合性分子軌道が生成され、そこでは核間にノードが存在します。
同様に、p 軌道の波動関数は、逆位相の 2 つのローブを生じます。 p 軌道が端から端まで重なると、σ 軌道と σ* 軌道が作成されます。 2 つの p 軌道が隣り合って重なり合うと、π 結合性および π* 反結合性の分子軌道が生成されます。
塗りつぶされた分子軌道図は、結合性および反結合性分子軌道内の電子の数を示します。 電子は、結合性軌道を占有する場合にのみ、結合性相互作用に寄与します。 分子の結合強度に対する電子の正味の寄与は、次のように計算される結合次数から決定されます。
<img alt="Figure1" src="/files/ftp_upload/11687/11687%20PT%20equation%201.png" style="text-align: center; height: 40px;">
結合順序は共有結合の強さの目安です。 結合次数が増加するにつれて、2 つの特定の原子間の結合はより強くなります。 分子軌道内の電子の分布により結合次数がゼロになる場合、安定した結合は形成されません。
分子軌道理論は多原子分子にも役立ちます。 sp2 混成炭素原子を含む平面六角形構造を持つベンゼン (C6H6) のルイスモデルは、その非局在化電子を正確に表すことができません。 しかし、分子軌道理論では、これらの電子は炭素環全体を覆う 3 つの π 結合分子軌道に割り当てられます。 これにより、完全に占有された (電子 6 個) セットの結合分子軌道が生成され、ベンゼン環に熱力学的および化学的安定性がさらに高まります。

MO理論と共有結合

分子軌道理論は、原子軌道の電子の分布と同様の方法で、分子内の電子の分布を説明しています。...

Education

JoVE Core

Organic Chemistry

有機化学

Unit 1

ユニット1

Covalent Bonding and Structure

共有結合と構造

KEY TERMS AND CONCEPTS

主要用語と概念

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

Electronegativity in Polar Covalent Bonds

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vsepr theory

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Predicting Shape and Molecular Polarity

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resonance and hybrid structures

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valence bond theory and hybridized orbitals

valence-bond-theory-and-hybridized-orbitals

Covalent Bond Overlap and Orbital Hybridization

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mo theory and covalent bonding

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intermolecular forces and physical properties

intermolecular-forces-and-physical-properties

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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
  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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