Sigma bond

Definition

A sigma bond is a type of covalent bond formed when two atomic orbitals overlap along the axis connecting the two bonding nuclei. This bond allows for free rotation around the bond axis and is characterized by a single pair of electrons shared between two atoms. Sigma bonds are essential in the formation of molecules and contribute to their stability and geometry.

5 Must Know Facts For Your Next Test

1. Sigma bonds are the strongest type of covalent bonds due to their head-on overlap of orbitals, leading to greater electron density between the nuclei.
2. In molecules with multiple bonds, each double bond consists of one sigma bond and one pi bond, while each triple bond has one sigma and two pi bonds.
3. Sigma bonds can be formed between different types of orbitals, including s-s, s-p, and p-p orbitals, making them versatile in bonding.
4. The rotation around a sigma bond is unrestricted because the electron density is concentrated along the axis of the bond, unlike pi bonds which create restrictions.
5. Molecular shapes and geometries, like linear or tetrahedral, are heavily influenced by the presence and arrangement of sigma bonds in a molecule.

Review Questions

• How does the formation of a sigma bond differ from that of a pi bond in terms of orbital overlap?
  • A sigma bond forms through the end-to-end overlap of atomic orbitals along the axis connecting two nuclei, resulting in maximum electron density directly between them. In contrast, a pi bond arises from the side-to-side overlap of p orbitals, with electron density located above and below this axis. This difference in overlap leads to varying strengths and rotational characteristics for these types of bonds.
• Discuss how hybridization contributes to the formation of sigma bonds and how this affects molecular geometry.
  • Hybridization involves mixing atomic orbitals to create new hybrid orbitals that optimize overlap during bonding. For example, in methane (CH₄), the sp³ hybridization results in four equivalent sp³ hybrid orbitals forming four sigma bonds with hydrogen atoms. This arrangement determines the tetrahedral geometry of methane, demonstrating how hybridization influences both bonding and shape in molecules.
• Evaluate the importance of sigma bonds in determining molecular stability and behavior during chemical reactions.
  • Sigma bonds play a crucial role in molecular stability due to their strong head-on overlap, providing significant electron density between bonded atoms. This stability influences how molecules interact during chemical reactions; for instance, while sigma bonds allow for rotation and flexibility within a molecule, they also define which bonds must be broken for reactions to occur. Understanding sigma bonds helps predict reactivity patterns and mechanisms in various chemical contexts.

Related terms

pi bond: A pi bond is a type of covalent bond that occurs when two atomic orbitals overlap side-by-side, resulting in electron density above and below the plane of the nuclei. Pi bonds usually accompany sigma bonds in double and triple bonds.

covalent bond: A covalent bond is a chemical bond formed by the sharing of electrons between atoms. Covalent bonds can be classified as single, double, or triple bonds based on the number of shared electron pairs.

hybridization: Hybridization is the process of combining atomic orbitals to form new hybrid orbitals that can explain molecular geometry and bonding properties in molecules.