Sigma bond

Definition

A sigma bond is a type of covalent bond formed by the head-on overlapping of atomic orbitals, allowing for a single bond between two atoms. This overlap can involve s orbitals, p orbitals, or hybridized orbitals, creating a bond that is characterized by its cylindrical symmetry about the bond axis. Sigma bonds are the first bonds formed between atoms and play a crucial role in determining molecular geometry and stability.

5 Must Know Facts For Your Next Test

1. Sigma bonds are stronger than pi bonds due to the direct overlap of orbitals, resulting in greater electron density along the bond axis.
2. Every single bond in a molecule is a sigma bond, while double and triple bonds contain one sigma bond and one or two pi bonds, respectively.
3. In terms of hybridization, sigma bonds form from hybrid orbitals such as sp, sp², and sp³, depending on the geometry of the molecule.
4. The presence of sigma bonds influences the molecular geometry; for example, molecules with only sigma bonds tend to adopt geometries like linear or tetrahedral based on the arrangement of these bonds.
5. Sigma bonds allow for free rotation about the bond axis, unlike pi bonds which restrict this rotation due to their orbital arrangement.

Review Questions

• How does the formation of a sigma bond differ from that of a pi bond, and what implications does this have for molecular structure?
  • A sigma bond forms from the head-on overlap of atomic orbitals, resulting in a strong bond characterized by cylindrical symmetry along the bond axis. In contrast, a pi bond forms from side-to-side overlapping of p orbitals and exists above and below this axis. This difference affects molecular structure significantly; while sigma bonds allow for free rotation around the bond axis, pi bonds create rigidity in double and triple bonded molecules, influencing their geometric arrangement.
• Discuss how hybridization relates to the formation of sigma bonds and its impact on molecular geometry.
  • Hybridization plays a key role in the formation of sigma bonds by allowing atomic orbitals to mix and create new hybrid orbitals that dictate bonding angles and shapes. For example, sp³ hybridization results in tetrahedral geometry with 109.5-degree angles due to four equivalent sigma bonds. The type of hybridization (sp, sp², sp³) directly impacts how atoms are arranged in three-dimensional space and thus influences the overall molecular structure.
• Evaluate the significance of sigma bonds in determining molecular properties such as strength and reactivity compared to other types of bonds.
  • Sigma bonds are fundamental to understanding molecular properties as they provide greater strength than pi bonds due to their direct orbital overlap. This strength contributes to the overall stability of molecules and affects their reactivity; for example, molecules with multiple sigma bonds may resist certain reactions until these bonds are broken. Furthermore, since sigma bonds permit free rotation around their axes while pi bonds do not, they influence not just molecular strength but also aspects like conformational isomerism and reactivity patterns in organic chemistry.

Related terms

pi bond:

A pi bond is a type of covalent bond formed when two lobes of one atomic orbital overlap with two lobes of another, resulting in a bond that exists above and below the plane of the atoms. Pi bonds usually accompany sigma bonds in double and triple bonds.

hybridization: Hybridization is the process of combining atomic orbitals to form new hybrid orbitals that can accommodate the bonding requirements of atoms, influencing the shape and type of bonds formed in a molecule.

covalent bond: A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms, which can result in single, double, or triple bonds depending on the number of shared pairs.