Sigma orbital

Definition

A sigma orbital is a type of molecular orbital formed by the head-on overlap of atomic orbitals, resulting in a cylindrical shape of electron density along the bond axis. This kind of bonding interaction is crucial for understanding the structure and stability of molecules, as sigma bonds are typically the strongest type of covalent bond found in nature, allowing for single bonds between atoms.

5 Must Know Facts For Your Next Test

1. Sigma orbitals can be formed from the overlap of two s orbitals, an s and a p orbital, or two p orbitals oriented along the bond axis.
2. In a diatomic molecule, the formation of a sigma bond is typically the first step in bonding, followed by the potential formation of pi bonds if additional overlaps occur.
3. Sigma bonds allow for free rotation around the bond axis due to their symmetrical electron distribution, unlike pi bonds which restrict this rotation.
4. Each sigma bond corresponds to one shared pair of electrons between two atoms, establishing a strong and stable connection in the molecule.
5. The energy of a sigma bond is lower than that of the individual atomic orbitals from which it forms, contributing to molecular stability.

Review Questions

• How does the formation of a sigma orbital differ from that of a pi orbital?
  • The formation of a sigma orbital involves head-on overlap of atomic orbitals, leading to electron density concentrated along the bond axis. In contrast, a pi orbital forms from side-to-side overlap of p orbitals, resulting in electron density located above and below this axis. This fundamental difference contributes to the strength and characteristics of the bonds formed; sigma bonds are generally stronger than pi bonds due to their direct overlap.
• Discuss the significance of sigma orbitals in determining molecular geometry and stability.
  • Sigma orbitals play a crucial role in determining both molecular geometry and stability. Since they are formed by direct overlap along the bond axis, they establish a strong connection between bonded atoms. This allows for predictability in geometric arrangements based on VSEPR theory. Furthermore, because sigma bonds have lower energy than unbonded atomic orbitals, they contribute significantly to overall molecular stability.
• Evaluate how understanding sigma orbitals can enhance our comprehension of chemical reactivity in organic compounds.
  • Understanding sigma orbitals is essential for grasping how organic compounds react chemically. Sigma bonds serve as foundational links between atoms within molecules and can influence reactivity patterns. By recognizing that sigma bonds allow for rotation and flexibility while being stronger than pi bonds, we can predict how molecules will orient during reactions. Additionally, knowing that breaking sigma bonds generally requires more energy than breaking weaker pi bonds helps explain why certain reactions proceed under specific conditions.

Related terms

pi orbital: A pi orbital is a type of molecular orbital formed by the side-to-side overlap of p orbitals, which results in electron density above and below the bond axis, typically found in double and triple bonds.

molecular orbital: A molecular orbital is a region in a molecule where electrons are likely to be found, formed from the combination of atomic orbitals, which can be bonding, antibonding, or non-bonding.

covalent bond: A covalent bond is a chemical bond formed when two atoms share one or more pairs of electrons, which can involve different types of orbitals and bonding interactions.