1. High School Chemistry - Core Concept Cheat Sheet
17: Molecular Geometry - VSEPR
Key Structure Terms
Molecular Geometries
 Valence Shell: Electrons in the outermost shell that are
involved in bonding.
A = central atom; X = ligands; E = lone pairs
Electron
Regions
2
 Lewis Structure: A 2D representation of a molecule and
its bonds.
 Lone Pair: Pair of electrons not being shared in a bond.
Molecular
Formula
AX2
Name
Shape
Linear
(BeCl2, CO2)
 Bonding Pair: Pair of electrons used to make a bond.
Both atoms sharing the electrons can “count” them in their
valence shell.
3
AX3
 Single bond: One pair of shared electrons.
(BF3, CO32-,
NO3-, SO3)
 Double bond: Two pairs of shared electrons. Shorter and
stronger than a single bond.
AX2E
 Triple bond: Three pairs of shared electrons. Shorter and
stronger than a double bond.
Trigonal
Planar
(NO2-, SO2,
O3)
 Valence Shell Electron Pair Repulsion Theory
(VSEPR): Bonds and lone pairs are electrons, all electrons
are negative, negative things repel other negative things,
therefore all bonds and lone pairs arrange themselves in 3D
as far away from each other as possible.
4
AX4
(CH4, NH4+,
PO43-, SO42-,
ClO4-)
AX3E
 Electron Geometry: 3D structure of a molecule
determined by counting the electron regions around a
central atom (bonds and lone pairs).
(NH3, H3O+,
PCl3, SO32-)
 Electron Region: Each bond (single, double or triple) and
lone pair count as “1” electron region.
AX2E2
 Molecular Geometry: 3D structure determined by the
atoms bonded to the central atom.
Bent
Tetrahedron
Trigonal
pyramidal
(H2O, ClO2-,
OF2, SCl2)
5
 Ligand: Atoms bonded to the central atom.
AX5
(PCl5)
VSEPR Theory and Geometry
Electron geometry is determined by looking at the number
of electron regions around the central atom.
AX4E
Molecular geometry is determined by looking at the
number of atoms bonded to the central atom (ligand) and
the number of lone pairs around the central atom.
Trigonal
bipyramidal
See-saw
(SF4, SCl4)
AX3 E2
Electronic Geometry Mnemonic: Linear(2) – Trigonal
Planar(3) – Tetrahedral (4) – Trigonal Bipyramidal(5) –
Octahedron(6) = “Long TriP To TriBe Overseas.”
T-shaped
(ClF3, ICl3)
AX2E3
Examples:
H
H C H
H
Bent
Linear
(XeF2, I3-)
6
AX6
Octahedron
(SF6, PCl6-)
Electron geometry: Tetrahedron
Molecular geometry: Tetrahedron
AX5E
(BrF5, IF5)
H N H
AX4 E2
H
(XeF4)
Square
pyramidal
Square
planar
Electron geometry: Tetrahedron
Molecular geometry: Trigonal pyramidal
How to Use This Cheat Sheet: These are the keys related to this topic. Try to read through it carefully twice then write it out on a blank
sheet of paper. Review it again before the exams.
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