Beginner Topic 152 of 1102 Bonding & Molecular Structure
Molecular Geometry
The three-dimensional arrangement of atoms only, ignoring lone pairs.
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In-depth explanation of Molecular Geometry
Molecular geometry is the three-dimensional arrangement of the atomic nuclei in a molecule and describes only the positions of the atoms. Lone pairs are not atoms, so they are not seen in the molecular shape, although they strongly influence the bond angles and distortions. Molecular geometry determines properties such as dipole moment and polarity, and it also controls how a molecule fits into a receptor or enzyme active site. It is derived from the electron domain geometry by removing the lone pair positions from the description. Bond angles and bond lengths are usually reported alongside it.
Going deeper: Molecular Geometry
Key ideas: Read the shape from AXnEm: AX2 linear, AX3 trigonal planar, AX2E bent, AX4 tetrahedral, AX3E pyramidal, AX2E2 bent, AX5 trigonal bipyramidal, AX4E see-saw, AX3E2 T-shaped, AX2E3 linear, AX6 octahedral, AX5E square pyramidal, AX4E2 square planar. Give angles with the expected deviation for lone pairs.
Common mistakes and connections: Frequent mistake: using the electron geometry name as the molecular shape, such as calling NH3 tetrahedral. Another is assuming the shape is flat because the Lewis structure is drawn flat on paper. Links to polarity, chirality, enzyme binding, spectroscopy and VSEPR.
Visualization of Molecular Geometry
Water has a tetrahedral electron arrangement but only atoms are counted for shape, so the molecule is bent with an H-O-H angle of 104.5 degrees. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Ammonia has a trigonal pyramidal molecular geometry, with three N-H bonds and one lone pair on nitrogen.
Frequently asked questions about Molecular Geometry
What is Molecular Geometry?
The three-dimensional arrangement of atoms only, ignoring lone pairs.
Is Molecular Geometry a beginner, intermediate or advanced topic?
Molecular Geometry is a beginner topic in Bonding & Molecular Structure. It needs no earlier chemistry lessons and is a good starting point.
What should I learn before Molecular Geometry?
Study these earlier topics in Bonding & Molecular Structure first: Doping, VSEPR Theory, Electron Domain Geometry.
What comes after Molecular Geometry?
The next topics in Bonding & Molecular Structure are Linear Geometry and Trigonal Planar Geometry.
Can I practise Molecular Geometry with quizzes?
Yes. The interactive lesson includes a self-check question on Molecular Geometry, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Where Molecular Geometry fits in Bonding & Molecular Structure
Molecular Geometry is topic 37 of 104 in Bonding & Molecular Structure.