Pi bond

Definition

A pi bond is a type of covalent bond formed by the lateral overlap of p orbitals from adjacent atoms, resulting in electron density above and below the internuclear axis. This bond usually occurs in conjunction with a sigma bond, contributing to the overall stability and geometry of molecules. Pi bonds are essential in determining the reactivity and properties of unsaturated compounds, such as alkenes and alkynes.

5 Must Know Facts For Your Next Test

1. Pi bonds are generally weaker than sigma bonds due to the less effective overlap of p orbitals compared to the head-on overlap of orbitals in sigma bonds.
2. The presence of pi bonds restricts the rotation around the bonded atoms, leading to geometric isomerism in compounds with multiple bonds.
3. In polyatomic molecules, pi bonds can contribute to resonance structures, allowing for delocalization of electrons across multiple atoms.
4. Pi bonds are commonly found in compounds with multiple bonds, such as alkenes (which have one double bond) and alkynes (which have one triple bond).
5. The formation of pi bonds is critical in understanding the behavior and properties of conjugated systems, which can exhibit unique optical and electronic characteristics.

Review Questions

• How do pi bonds influence the geometry and reactivity of molecules?
  • Pi bonds significantly influence molecular geometry by restricting rotation around double or triple bonded atoms. This restriction can lead to different spatial arrangements, known as geometric isomers. Additionally, pi bonds increase reactivity because they are typically more reactive than sigma bonds, making unsaturated compounds more likely to undergo reactions such as addition reactions with electrophiles.
• Compare and contrast sigma bonds and pi bonds in terms of their formation and characteristics.
  • Sigma bonds are formed by the head-on overlap of atomic orbitals, providing strong bonding with free rotation around the bond axis. In contrast, pi bonds result from the side-to-side overlap of p orbitals, which creates electron density above and below the internuclear axis. While sigma bonds are generally stronger and allow rotation, pi bonds introduce rigidity into molecular structures and play a key role in determining molecular shape and reactivity.
• Evaluate the role of pi bonds in resonance structures and their implications for molecular stability.
  • Pi bonds play a crucial role in resonance structures by allowing for electron delocalization across multiple atoms. This delocalization stabilizes molecules because it spreads out electron density over a larger area rather than localizing it between two atoms. The presence of resonance increases molecular stability and lowers energy levels, making molecules more stable than if they had fixed single or double bonds without resonance contributions.

Related terms

sigma bond:

A sigma bond is the strongest type of covalent bond formed by the end-to-end overlap of atomic orbitals, allowing for free rotation around the bond axis.

double bond: A double bond consists of one sigma bond and one pi bond, typically found in alkenes, which increases the bond strength and rigidity compared to single bonds.

molecular orbital theory: Molecular orbital theory describes how atomic orbitals combine to form molecular orbitals, which can be occupied by electrons and play a crucial role in bonding and molecular stability.