VSEPR Theory and Molecular Geometry: Key Concepts and Shapes in Chemistry
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27 Terms
VSEPR
Valence Shell Electron Pair Repulsion theory; predicts molecular shape because electron pairs repel and spread out as far apart as possible.
Valence Electrons
Electrons in the outermost energy level of an atom that are used in bonding.
Electron Domain
A region of electrons around a central atom; each bond and lone pair counts as one electron domain.
Molecular Geometry
The shape of a molecule based only on the positions of the atoms.
Electron Geometry
The arrangement of all electron domains (bonds and lone pairs) around a central atom.
Molecular Formula
A formula showing the actual number of each type of atom in a molecule (ex. H₂O, CO₂).
Lewis Structure
A diagram showing valence electrons, bonds, and lone pairs in a molecule.
Tetrahedral
A molecular shape with 4 bonding pairs and 0 lone pairs around the central atom; bond angle 109.5°; example CH₄.
Trigonal Pyramidal
A molecular shape with 3 bonding pairs and 1 lone pair around the central atom; example NH₃.
Linear
A molecular shape in which atoms form a straight line; bond angle 180°; example CO₂.
Trigonal Planar
A molecular shape with 3 bonding pairs and 0 lone pairs around the central atom; bond angle 120°; example BF₃.
Bent
A molecular shape caused by lone pairs pushing bonded atoms closer together; example H₂O.
Nonbonded Electron Pair
A pair of valence electrons that is not shared in a bond; also called a lone pair.
Lone Pair
A pair of valence electrons not involved in bonding.
CH₄ Shape
Tetrahedral.
NH₃ Shape
Trigonal Pyramidal.
H₂O Shape
Bent.
CO₂ Shape
Linear.
BF₃ Shape
Trigonal Planar.
Difference Between Electron Geometry and Molecular Geometry
Electron geometry includes all electron domains; molecular geometry only includes the positions of atoms.
What Determines Molecular Shape?
Repulsion between electron domains around the central atom.
Which Repels More Strongly?
Lone pairs repel more strongly than bonding pairs.
Electron Geometry of CH₄
Tetrahedral.
Electron Geometry of NH₃
Tetrahedral.
Electron Geometry of H₂O
Tetrahedral.
Molecular Geometry of NH₃
Trigonal Pyramidal.
Molecular Geometry of H₂O
Bent.