Sigma bond

Definition

A sigma bond is a type of covalent bond that is formed when two atomic orbitals overlap along the axis connecting the two nuclei. This bond is characterized by its cylindrical symmetry around the bond axis, allowing for free rotation of the bonded atoms. Sigma bonds are fundamental to the structure of molecules and play a key role in both molecular orbital theory and valence bond theory, as they help explain how atoms combine to form stable compounds.

5 Must Know Facts For Your Next Test

1. Sigma bonds are the strongest type of covalent bond due to the direct overlap of atomic orbitals, which maximizes electron density between the nuclei.
2. Every single bond between atoms is a sigma bond, while double and triple bonds consist of one sigma bond and one or more pi bonds.
3. In molecular orbital theory, sigma bonds are formed from the combination of s and p orbitals, contributing to the bonding characteristics of diatomic and polyatomic molecules.
4. The formation of sigma bonds influences molecular geometry and contributes to the shape of molecules according to VSEPR theory.
5. Sigma bonds allow for free rotation about the bond axis, unlike pi bonds, which restrict rotation due to their lateral overlap.

Review Questions

• How does the concept of sigma bonds enhance our understanding of molecular structure in chemical bonding?
  • Understanding sigma bonds helps us grasp how atoms share electrons to form stable structures. In molecular bonding, sigma bonds are the primary links between atoms, establishing the basic framework of molecular geometry. They allow for free rotation around the bond axis, which can affect the spatial arrangement of substituents in larger molecules. This understanding also aids in predicting molecular shapes and reactivity.
• Compare and contrast sigma bonds with pi bonds in terms of their formation and influence on molecular geometry.
  • Sigma bonds are formed through the end-to-end overlap of atomic orbitals along the bond axis, while pi bonds result from lateral overlap above and below this axis. Sigma bonds allow for free rotation between bonded atoms, contributing to flexible molecular shapes, whereas pi bonds restrict this rotation due to their orientation. This difference plays a crucial role in determining the physical properties and reactivity of molecules, especially in unsaturated compounds where double or triple bonding exists.
• Evaluate the significance of hybridization in forming sigma bonds and how it affects molecular geometry.
  • Hybridization is essential for creating new orbitals that facilitate the formation of sigma bonds, leading to stronger connections between atoms. By combining different atomic orbitals—such as s and p—hybridization results in unique hybrid orbitals that optimize bonding angles and molecular shapes. This process directly influences molecular geometry as it determines how many sigma bonds can be formed and their spatial arrangement, which ultimately impacts the reactivity and properties of compounds.

Related terms

pi bond:

A pi bond is a type of covalent bond that occurs when two atomic orbitals overlap laterally, above and below the bond axis, and is typically found alongside sigma bonds in double and triple bonds.

hybridization: Hybridization is the process of mixing atomic orbitals to create new hybrid orbitals that can form stronger bonds, such as sigma bonds, in molecules.

covalent bond: A covalent bond is a chemical bond formed when two atoms share one or more pairs of electrons, including both sigma and pi bonds.