Sigma bond

Definition

A sigma bond is a type of covalent bond formed when two atomic orbitals overlap head-on, allowing for the sharing of electron density along the axis connecting the two nuclei. This bond is characterized by its cylindrical symmetry and is the first bond formed between two atoms in a molecule, playing a crucial role in the molecular structure 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, providing greater electron density between the nuclei.
2. In hybridization, atomic orbitals combine to form new hybrid orbitals, which can create multiple sigma bonds in molecules with different geometries.
3. Every single covalent bond in a molecule is a sigma bond, while double and triple bonds contain one sigma bond and one or more pi bonds.
4. Sigma bonds allow for free rotation around the bond axis, unlike pi bonds which create rigidity in molecular structures.
5. The presence of sigma bonds contributes significantly to the stability and geometry of molecules, influencing their chemical reactivity.

Review Questions

• How do sigma bonds differ from pi bonds in terms of their formation and characteristics?
  • Sigma bonds are formed through the head-on overlap of atomic orbitals, resulting in a cylindrical symmetry around the bond axis. In contrast, pi bonds arise from side-by-side overlap of p orbitals, creating a nodal plane along the internuclear axis. This fundamental difference makes sigma bonds stronger than pi bonds and allows for rotation around sigma bonds but restricts rotation around pi bonds.
• Discuss how hybridization leads to the formation of sigma bonds in molecules with different geometries.
  • Hybridization involves mixing atomic orbitals to create new hybrid orbitals that have specific shapes and energies. For example, sp³ hybridization leads to tetrahedral geometry with four equivalent sp³ hybrid orbitals forming four sigma bonds. In contrast, sp² hybridization results in trigonal planar geometry with three sp² orbitals forming three sigma bonds and one remaining p orbital used for forming a pi bond. This process helps explain molecular shapes and bonding patterns in various compounds.
• Evaluate the significance of sigma bonds in determining molecular stability and reactivity.
  • Sigma bonds are crucial for molecular stability as they represent the primary means by which atoms share electrons and form stable connections. The strength of these bonds allows molecules to maintain their structure under various conditions. Additionally, because sigma bonds permit free rotation, they influence how molecules interact during chemical reactions. Understanding sigma bonds aids in predicting reactivity patterns, as the presence or absence of pi bonds can significantly alter how molecules behave in different environments.

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 a bond that has a nodal plane along the internuclear axis and is generally weaker than a sigma bond.

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

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