Electron and Molecular Geometries

Electron and Molecular Geometries

Key Terms and Definitions

  • Electron Groups: Groups around a central atom that influence its geometrical arrangement. Each of the following counts as one electron group:

    • Lone pairs

    • Single bonds

    • Double bonds

    • Triple bonds

    • Single electrons

Summary of Geometries and Bond Angles

  • Linear Geometry

    • Electron Groups: 2

    • Bonding Groups: 2

    • Lone Pairs: 0

    • Bond Angles: 180°

    • Example: $0=C=0$

  • Trigonal Planar Geometry

    • Electron Groups: 3

    • Bonding Groups: 3

    • Lone Pairs: 0

    • Bond Angles: 120°

    • Example: $F-B-F$

    • Molecular Geometry: Bent

    • Electron Groups: 3

    • Bonding Groups: 2

    • Lone Pairs: 1

    • Bond Angles: <120°

    • Example: $0――0:H$

  • Tetrahedral Geometry

    • Electron Groups: 4

    • Bonding Groups: 4

    • Lone Pairs: 0

    • Bond Angles: 109.5°

    • Example: $H-C-H$

    • Molecular Geometry: Trigonal Pyramidal

    • Electron Groups: 4

    • Bonding Groups: 3

    • Lone Pairs: 1

    • Bond Angles: <109.5°

    • Example: $H-H-N-H$

    • Molecular Geometry: Bent

    • Electron Groups: 4

    • Bonding Groups: 2

    • Lone Pairs: 2

    • Bond Angles: <109.5°

  • Trigonal Bipyramidal Geometry

    • Electron Groups: 5

    • Bonding Groups: 5

    • Lone Pairs: 0

    • Bond Angles: 120° (equatorial), 90° (axial)

    • Example: $C:$

    • Molecular Geometry: Seesaw

    • Electron Groups: 5

    • Bonding Groups: 4

    • Lone Pairs: 1

    • Bond Angles: <120° (equatorial), <90° (axial)

    • Molecular Geometry: T-shaped

    • Electron Groups: 5

    • Bonding Groups: 3

    • Lone Pairs: 2

    • Bond Angles: <90°

    • Molecular Geometry: Linear

    • Electron Groups: 5

    • Bonding Groups: 2

    • Lone Pairs: 3

    • Bond Angles: 180°

  • Octahedral Geometry

    • Electron Groups: 6

    • Bonding Groups: 6

    • Lone Pairs: 0

    • Bond Angles: 90°

    • Molecular Geometry: Square Pyramidal

    • Electron Groups: 6

    • Bonding Groups: 5

    • Lone Pairs: 1

    • Bond Angles: <90°

    • Molecular Geometry: Square Planar

    • Electron Groups: 6

    • Bonding Groups: 4

    • Lone Pairs: 2

    • Bond Angles: 90°

    • Example: $F-xe-F$

Conclusion

Understanding electron geometries and molecular shapes is crucial for predicting the spatial arrangement and reactivity of molecules. The geometries depend on the number of electron groups around the central atom, influencing bond angles and overall molecular structure.