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Understanding Sigma and Pi Bond Formation

Apr 25, 2025

Sigma and Pi Bonds: Understanding Orbital Overlaps

Introduction to Electron Orbitals

  • Electrons are found in distinct orbitals: s, p, d, and f.
  • The octet rule is crucial for atomic stability, achieved when main energy levels are filled with the maximum electrons.

Bond Formation

  • Ionic Bonds: Form when an orbital gains or loses electrons.
  • Covalent Bonds: Occur when electrons are shared between orbitals to satisfy the octet rule.

Sigma Bonds

  • Definition: A covalent bond where two orbitals overlap head-on.
  • Characteristics:
    • Typically involves two s-orbitals, forming a hydrogen molecule.
    • Sigma bonds can result from different overlaps:
      • s-orbitals to s-orbitals
      • s-orbitals to p-orbitals
      • p-orbitals to p-orbitals
  • Visual Representation: Illustrated in diagrams showing head-on overlap, such as Figure 1 showing two s-orbitals in hydrogen.
  • Nomenclature: Represented by the Greek symbol sigma (σ).

Properties of Sigma Bonds

  • Single Bonds: Always sigma bonds, with the electron pair located in the shared space of overlap.
  • Terminology: Head-on overlap is also referred to as axial or end-to-end overlap.

View note sourcehttps://app.kognity.com/study/app/septima-chemistry/sid-426-cid-329683/book/sigma-and-pi-bonds-hl-id-45138/Sigma bonds Electrons are found in orbitals; s, p, d and f (see section S1.3.3–4). When the main energy level is filled with the maximum number of electrons it can hold, the octet rule has been fulfilled and atoms are stable. When an orbital is partially empty, it will gain or lose electrons (ionic bond), or it will share electrons (covalent bond) so it can then fulfil the octet rule. Considered what happens to the different orbitals in an atom when the electrons they contain form a pair. You can see this in Figure 1, which shows a single bond forming between s-orbitals in two hydrogen atoms and results in a hydrogen molecule. Diagram showing the head-on overlap of two s-orbitals forming a hydrogen molecule. [AI] Figure 1. The head-on overlap of two s-orbitals in hydrogen. As you can see in Figure 1, a covalent bond is formed when two orbitals overlap, each one containing one electron. If this orbital-overlap is a head-on overlap, it is known as a sigma bond , and the electron pair is likely to be found in that overlapping shared space. Single bonds are always sigma bonds, which are represented with the Greek symbol for sigma, σ. Sigma bonds can be formed from the head-on overlap of s-orbitals to s-orbitals, s-orbitals to p-orbitals, or p-orbitals to p-orbitals (Figure 2). Note that this head-on overlap can also be referred to as an axial overlap or end-to-end overlap.