Atomic orbital hybridization mixes atomic orbitals to create new hybrid orbitals with different shapes and energies. This process enables stronger, more stable covalent bonds when atoms bond with others, combining s, p, and sometimes d orbitals.

Hybrid orbitals have unique shapes and orientations that minimize electron repulsion and maximize bond strength. The type of hybridization can be predicted based on molecular geometry and the number of electron domains surrounding the central atom.

Atomic Orbital Hybridization

Process of orbital hybridization

• Involves mixing atomic orbitals to create new hybrid orbitals with different shapes and energies
  • Enables formation of stronger, more stable covalent bonds when an atom bonds with other atoms
  • Combines s, p, and sometimes d orbitals of an atom
    • s and p orbitals mix to form sp, sp², or sp³ hybrid orbitals (methane, ethene, ethyne)
    • d orbitals can also hybridize, forming sp³d or sp³d² hybrid orbitals (phosphorus pentachloride, sulfur hexafluoride)
• Hybrid orbitals possess unique shapes and orientations that minimize electron repulsion and maximize bond strength
  • sp hybrid orbitals are linear and oriented 180° apart (ethyne)
  • sp² hybrid orbitals are trigonal planar and oriented 120° apart (ethene)
  • sp³ hybrid orbitals are tetrahedral and oriented 109.5° apart (methane)
• Number of hybrid orbitals formed equals the number of atomic orbitals participating in hybridization
• Unhybridized atomic orbitals may remain and can form pi ($\pi$) bonds or exist as lone pairs (ethene, water)

Prediction of hybrid orbital types

• Hybridization of the central atom is predictable based on molecular geometry and number of electron domains (bonding and lone pairs) surrounding it
  1. Linear geometry (2 electron domains): sp hybridization (beryllium chloride)
  2. Trigonal planar geometry (3 electron domains): sp² hybridization (boron trifluoride)
  3. Tetrahedral geometry (4 electron domains): sp³ hybridization (methane)
  4. Trigonal bipyramidal geometry (5 electron domains): sp³d hybridization (phosphorus pentachloride)
  5. Octahedral geometry (6 electron domains): sp³d² hybridization (sulfur hexafluoride)
• Lone pairs on the central atom can affect molecular geometry without changing hybridization
  • Bent (2 bonding domains + 1 lone pair): sp² hybridization (sulfur dioxide)
  • Trigonal pyramidal (3 bonding domains + 1 lone pair): sp³ hybridization (ammonia)
  • Seesaw (4 bonding domains + 1 lone pair): sp³d hybridization (sulfur tetrafluoride)
  • T-shaped (3 bonding domains + 2 lone pairs): sp³d hybridization (chlorine trifluoride)
  • Square pyramidal (5 bonding domains + 1 lone pair): sp³d² hybridization (bromine pentafluoride)
• Valence shell electron pair repulsion (VSEPR) theory helps predict molecular geometry based on electron domain arrangements

Shapes of hybrid vs atomic orbitals

• Atomic orbitals have distinct shapes and orientations
  • s orbitals are spherical (hydrogen 1s)
  • p orbitals are dumbbell-shaped and oriented along x, y, and z axes (carbon 2p)
  • d orbitals have more complex shapes and orientations (iron 3d)
• Hybrid orbitals differ in shape and orientation compared to atomic orbitals
  • sp hybrid orbitals are linear and oriented 180° apart (ethyne)
    • Formed by mixing one s and one p orbital
  • sp² hybrid orbitals are trigonal planar and oriented 120° apart (ethene)
    • Formed by mixing one s and two p orbitals
  • sp³ hybrid orbitals are tetrahedral and oriented 109.5° apart (methane)
    • Formed by mixing one s and three p orbitals
• Shapes and orientations of hybrid orbitals enable formation of stronger, more stable covalent bonds vs atomic orbitals alone
• Unhybridized atomic orbitals maintain original shapes and orientations and can form pi ($\pi$) bonds or exist as lone pairs (ethene, water)

Molecular Structure and Bonding

• Molecular orbital theory provides a more accurate description of electron behavior in molecules
• Electron domains include both bonding and non-bonding electron pairs
• Bond angles between hybrid orbitals are influenced by electron-electron repulsion and molecular geometry