Name: covalent bond overlap and orbital hybridization
Uploaded: 2025-05-22T09:05:33.000Z
Duration: 2 min 38 s
Channel: JoVE

价键理论提出，化学键是通过部分填充的原子轨道重叠形成的，包括非球形的s轨道以外的其他轨道。
当两个非球形轨道之间形成单键时，这两个轨道将发生头对头重叠。
由原子轨道头对头重叠形成的共价键称为σ键。
s 和 p 轨道重叠形成共价键无法产生价层电子对互斥（VSEPR）模型中的各种分子构型。价键理论通过原子轨道的杂化（即混合）来解释这种分子几何结构。
参与成键的一些原子轨道会重新组合，形成新的轨道，其形状为原始轨道的杂化。原子轨道的初始数量与生成的杂化轨道数量始终相同。
杂化轨道与其组成的原子轨道具有不同的形状，其中一个瓣明显大于另一个瓣。因此，电子概率密度高度集中在具有方向性的大瓣区域，从而更有效地与其他原子的轨道发生重叠。为了清晰起见，这些轨道通常省略较小的瓣而绘制。
例如，在碳的激发态中，含有四个未成对电子的一个s轨道和三个p轨道发生杂化，形成四个等价的s-p-三杂化轨道，这些轨道位于正四面体的四个顶点上。
碳原子在激发态下，一个s轨道与两个p轨道杂化，形成三个具有平面三角形几何构型的等价s-p-双杂化轨道。
类似地，一个 s 轨道和一个 p 轨道的杂化可以形成两个相互呈 180 度取向的 sp 轨道。
杂化概念还可以解释多重键的形成。两个p轨道的侧向重叠形成一个π键。
然而，只有当两个原子之间已存在σ键时，才能在双键和三键中形成π键。由于π键位于核间轴的两侧，因此π键无法围绕该轴旋转。

价键理论和杂化轨道

Valence Bond Theory and Hybridized Orbitals

根据价键理论，当满足以下条件时，就会形成共价键:(1) 一个原子上的轨道与第二个原子上的轨道发生重叠; (2) 每个轨道中的单电子结合形成电子对。 共价键的强度取决于所涉及轨道的重叠程度。 当轨道在两个原子核之间的直线上重叠时，可以实现最大重叠。


 σ键（路易斯结构中的单键）是电子密度集中在核间轴的上共价键。 π 键是由两个 p 轨道并排重叠产生的共价键。 在 π 键中，轨道重叠区域位于核间轴的相对两侧，而沿轴有一个节点（没无电子存在的平面）。 所有单键都是σ键，而多重键由σ键和π键组成。


 当原子结合成分子时，原子轨道的波函数可以结合，产生具有新形状的数学描述。 这个过程称为杂化，通过原子轨道的线性组合完成， 由此产生的新轨道称为杂化轨道。


 杂化轨道仅在共价键合的原子中形成，其形状和方向与孤立原子中的原子轨道不同。 杂化轨道的数量等于生成它们的原子轨道数量。 一组杂化轨道中的所有轨道在形状和能量上等效，并且其方向由VSEPR理论预测。 杂化轨道重叠形成σ键，而未杂化轨道重叠形成π键。


 例如，在碳的激发态下，一个 2s 和三个 2p 轨道发生杂化，产生四个四面体取向的简并杂化 sp3 轨道。 在甲烷分子中，四个氢原子各自的 1s 轨道与碳原子的四个 sp3 轨道之一重叠，形成σ键。


 类似地，碳的1个2s和2个2p轨道的混合产生三个具有三角平面几何结构的等效sp2杂化轨道，而1个2s和1个2p轨道的杂化产生两个彼此成180°取向的sp轨道。


 对于在其价层中具有 d 轨道的原子，五个价层原子轨道（一个 s、三个 p 和一个 d 轨道）的杂化给出了五个sp3d 杂化轨道，呈三角双锥几何形状。 通过混合六个价层原子轨道（一个s、三个p和两个d轨道），可以获得六个sp3d2杂化轨道，形成八面体排列。



 本文改编自 <a href="https://openstax.org/books/chemistry-2e/pages/8-1-valence-bond-theory">Openstax, Chemistry 2e, Section 8.1 Valence Bond Theory</a> and <a href="https://openstax.org/books/chemistry-2e/pages/8-2-hybrid-atomic-orbitals">Section 8.2 Hybrid Atomic Orbitals</a>.

根据价键理论，共价键的形成条件是：（1）一个原子的轨道与另一个原子的轨道发生重叠，且（2）两个原子轨道中各有一个单...

valence-bond-theory-and-hybridized-orbitals

Education

教育

JoVE Core

Organic Chemistry

有机化学

Unit 1

第一单元

Covalent Bonding and Structure

共价键与结构

KEY TERMS AND CONCEPTS

关键术语与概念

covalent bond overlap and orbital hybridization

Covalent bonds form when orbitals on two atoms overlap and their single electrons pair up. The bond is stronger when the overlap is greater. Maximum overlap happens when the orbitals meet along a direct line between the two nuclei.

A sigma bond, or σ bond, is the kind of covalent bond found in a single bond in a Lewis structure. In a σ bond, electron density is concentrated along the internuclear axis. A pi bond, or π bond, forms when two p orbitals overlap side by side. In a π bond, the overlap lies on opposite sides of the internuclear axis, and a node with no electron probability lies along the axis. Single bonds are σ bonds, while multiple bonds include both σ and π bonds.

When atoms join in a molecule, atomic orbital wave functions can combine to make new orbital shapes. This process is called hybridization, and it is described by the linear combination of atomic orbitals. The new orbitals are called hybrid orbitals. They form only in covalently bonded atoms, and their shapes and orientations differ from those of atomic orbitals in isolated atoms. The number of hybrid orbitals matches the number of atomic orbitals used to make them. Orbitals in one hybrid set have the same shape and energy, and their directions follow VSEPR theory. Hybrid orbitals form σ bonds, while unhybridized orbitals form π bonds.

Carbon shows this pattern clearly. In its excited state, one 2s orbital and three 2p orbitals hybridize to form four equivalent sp3 orbitals arranged tetrahedrally. In methane, each hydrogen 1s orbital overlaps with one carbon sp3 orbital to make a σ bond. One 2s orbital and two 2p orbitals can also mix to make three equivalent sp2 orbitals with trigonal planar geometry. When one 2s orbital mixes with one 2p orbital, two sp orbitals form and point 180° apart.

Atoms with d orbitals in the valence shell can form larger hybrid sets. Mixing five valence shell atomic orbitals, one s, three p, and one d, gives five sp3d hybrid orbitals with trigonal bipyramidal geometry. Mixing six valence shell atomic orbitals, one s, three p, and two d, gives six sp3d2 hybrid orbitals with octahedral geometry.

Covalent Bond Overlap and Orbital Hybridization

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Learn how orbital overlap forms sigma and pi bonds, then see how hybridization creates sp3, sp2, sp, sp3d, and sp3d2 orbitals in molecules.

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Covalent Bond Overlap and Orbital Hybridization

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