1.8_ Hybridization - Chemistry LibreTexts

1.8: Hybridization

Hybridization was introduced to resolve the limitations of valence bond theory in predicting molecular structures. It helps understand the observed bond angles in organic compounds, commonly around 109.5°, 120°, or 180°. The framework of Valence Shell Electron Pair Repulsion (VSEPR) theory suggests that electron pairs repel each other, aiming to occupy positions that minimize this repulsion, leading to predictable molecular geometries.

Introduction to Hybridization (Example of CH₄)

• Ground state electron configuration of carbon shows two unpaired valence electrons, suggesting it could form two bonds (e.g., CH₂).

  • In practice this isn’t the case → so how does CH₄ exist?

    • for CH₄ to form → carbon’s configuration needs to have four unpaired electrons

  • sp³ Hybridization: Combines 2s (1 orbital) and 2p (3 orbitals) orbitals to yield four equivalent sp hybrid orbitals

    • (75% p and 25% s character).

  • Allows carbon to create four equal energy bonds

    • hybridized orbitals are more directional → greater overlap in bond formation → stronger bonds

    • hybridization leads to more stable compounds

Types of Hybridization

sp Hybridization

• Characteristics:

  • Forms four hybrid orbitals, 75% p and 25% s character.

  • Results in bond angles of approximately 109.5°, creating a tetrahedral structure.

• Example - Methane (CH₄):

  • Each sp orbital from carbon overlaps with the s orbitals from four hydrogen atoms.

  • Resulting shape: Tetrahedral, confirming stability due to minimized electron repulsion.

sp² Hybridization

• Characteristics:

  • The 2s and two 2p orbitals hybridize, resulting in three sp² orbitals (67% p and 33% s character).

  • The remaining p orbital remains perpendicular to this plane, forming a trigonal planar geometry with 120° bond angles.

• Example - Aluminum Trihydride (AlH₃):

  • One 2s and two 2p orbitals hybridize into three sp² orbitals, bonding with hydrogen through sp²-s overlap and achieving minimal repulsion.

sp Hybridization

• Characteristics:

  • Involves hybridizing one 2s and one 2p orbital, creating two sp orbitals (50% s and 50% p character).

  • Bonds formed exhibit a linear structure (180° angle) with minimal electron repulsion.

• Examples:

  • Ethyne (C₂H₂): Each carbon forms two sp hybrid orbitals allowing for linear geometry and two additional pi bonds due to remaining p orbitals.

  • Magnesium Hydride (MgH₂): Hybridization of 3s and a 3p orbital creates linear bonds with hydrogens.

Energy Changes During Hybridization

• Hybridization lowers the energy of electrons, promoting the formation of stable bonds.

• Directionality and increased overlap of hybridized orbitals result in stronger covalent bonds.

Summary of Bond Formation

• Hybridization accounts for complex bonding scenarios:

  • sp³ for tetrahedral structures (4 bonded atoms)

  • sp² for trigonal planar (3 bonded atoms)

  • sp for linear geometries (2 bonded atoms)

• The understanding of hybridization aids in predicting the geometry and reactivity of molecules in organic chemistry.