Pi bond

Definition

A pi bond is a type of covalent bond formed when two atomic orbitals overlap sideways, resulting in the sharing of electrons between two atoms. This bond typically occurs in addition to a sigma bond, which is the first bond formed between two atoms, and is crucial in determining the geometry and reactivity of molecules. Pi bonds are found in double and triple bonds and contribute to the delocalization of electrons in certain molecular structures.

5 Must Know Facts For Your Next Test

1. Pi bonds are weaker than sigma bonds due to their sideways overlap, making them more reactive and less stable.
2. In a double bond, one bond is a sigma bond and the other is a pi bond; in a triple bond, there are one sigma bond and two pi bonds.
3. The presence of pi bonds restricts rotation about the bonded atoms, leading to cis-trans isomerism in alkenes.
4. Pi bonds can contribute to resonance structures in molecules, allowing for greater stability through electron delocalization.
5. Pi bonds are typically formed by the overlap of p-orbitals from adjacent atoms, leading to specific molecular geometries.

Review Questions

• How do pi bonds influence molecular geometry and isomerism in compounds?
  • Pi bonds play a significant role in determining molecular geometry because they restrict rotation around the bond axis. In compounds like alkenes, where double bonds are present, this restriction leads to cis-trans isomerism, where different spatial arrangements of groups attached to the double-bonded carbon atoms can exist. As a result, pi bonds not only affect the shape of molecules but also their chemical behavior and reactivity.
• Compare and contrast the characteristics of sigma and pi bonds regarding their formation and strength.
  • Sigma bonds are formed by the head-on overlap of atomic orbitals, which provides strong bonding interactions that allow free rotation around the bond axis. In contrast, pi bonds result from sideways overlap of p-orbitals and are generally weaker than sigma bonds. While sigma bonds can exist independently as single bonds, pi bonds always accompany at least one sigma bond in double or triple bonding scenarios. This difference significantly impacts molecular stability and reactivity.
• Evaluate how pi bonds contribute to resonance in molecules and their overall stability.
  • Pi bonds significantly contribute to resonance by allowing for the delocalization of electrons across multiple atoms in a molecule. When a molecule can be represented by two or more valid Lewis structures, it indicates that pi electrons can shift positions while maintaining overall charge neutrality. This delocalization lowers the energy of the molecule, enhancing its stability. Resonance involving pi bonds allows molecules to distribute their electron density more evenly, leading to unique properties such as increased reactivity or stability compared to structures without resonance.

Related terms

sigma bond:

A sigma bond is the strongest type of covalent bond formed by the head-on overlapping of atomic orbitals, allowing for free rotation around the bond axis.

bond order: Bond order refers to the number of chemical bonds between a pair of atoms, indicating the stability and strength of a bond, with higher bond orders signifying stronger bonds.

resonance: Resonance is a phenomenon where a molecule can be represented by two or more valid Lewis structures, contributing to the overall electronic structure and stability of the molecule.