Molecular Geometry Study Pack

Kibin's free study pack on Molecular Geometry includes a 3-section study guide, 8 quiz questions, 10 flashcards, and 1 open-ended Explain review question. Sign up free to track your progress toward mastery, plus upload your own notes and recordings to create personalized study packs organized by course.

Last updated May 21, 2026

Topic mastery0%
Save progress →

Molecular Geometry Study Guide

Master the logic behind molecular shapes by working through VSEPR theory, electron vs. molecular geometry, and the five fundamental geometries — from linear to octahedral. See how lone pairs compress bond angles below ideal values and learn to predict molecular polarity by analyzing bond dipoles and symmetry. Perfect for students tackling shape-based reasoning and dipole moment problems.

Key Takeaways

  • •VSEPR theory predicts molecular geometry by assuming that electron groups around a central atom arrange themselves as far apart as possible to minimize repulsion.
  • •Electron geometry describes the arrangement of all electron groups (bonding and lone pairs), while molecular geometry describes only the arrangement of atoms.
  • •Lone pairs exert greater repulsion than bonding pairs, compressing bond angles below the idealized values predicted by electron geometry alone.
  • •The five fundamental electron geometries — linear, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral — each produce a family of molecular shapes depending on how many lone pairs replace bonding positions.
  • •Molecular polarity depends on both the polarity of individual bonds and the overall symmetry of the molecular geometry; symmetric arrangements of identical bonds cancel dipole moments, producing nonpolar molecules.
  • •Electronegativity differences between bonded atoms create bond dipoles, which are vector quantities that must be added together to determine the net molecular dipole moment.

VSEPR Theory: The Logic Behind Molecular Shape

Valence Shell Electron Pair Repulsion (VSEPR) theory provides the foundational framework for predicting three-dimensional molecular geometry based on the behavior of electron groups around a central atom.

Core Principle of Electron Repulsion

  • •Electron groups — which include single bonds, double bonds, triple bonds, and lone pairs — all carry negative charge and repel one another.
  • •Each of these groups, regardless of bond order, counts as one region of electron density for VSEPR purposes; a triple bond occupies one electron group position, not three.
  • •Electron groups distribute themselves around the central atom at maximum angular separation to achieve the lowest-energy, most stable arrangement.

Electron Groups vs. Bonding Positions

  • •The total number of electron groups determines the electron geometry, which is the spatial arrangement of all groups including lone pairs.
  • •The number of groups that are actual bonds to other atoms determines the molecular geometry, which describes only the positions of nuclei.
  • •A molecule can have the same electron geometry as another molecule but a completely different molecular shape if the number of lone pairs differs.

Electron Geometries and Their Idealized Bond Angles

Five parent electron geometries arise from arrangements of two through six electron groups around a central atom, each with a characteristic set of idealized bond angles.

Linear Arrangement: Two Electron Groups

  • •Two electron groups position themselves on opposite sides of the central atom, producing a bond angle of exactly 180°.
  • •Carbon dioxide (CO₂) exemplifies this geometry; the two double bonds act as two electron groups, giving a linear shape.

Trigonal Planar Arrangement: Three Electron Groups

  • •Three electron groups spread into a flat triangle around the central atom, with idealized bond angles of 120°.
  • •Boron trifluoride (BF₃), which has no lone pairs, is a textbook example of trigonal planar molecular geometry.

Tetrahedral Arrangement: Four Electron Groups

  • •Four electron groups point toward the corners of a tetrahedron, producing idealized bond angles of 109.5°.
  • •Methane (CH₄) achieves this geometry with four identical bonding pairs and no lone pairs.

Trigonal Bipyramidal Arrangement: Five Electron Groups

  • •Five electron groups occupy two distinct position types: three equatorial positions in a plane (120° apart) and two axial positions above and below the plane (90° from equatorial).
  • •Phosphorus pentachloride (PCl₅) represents this geometry with all five positions occupied by bonds.

Octahedral Arrangement: Six Electron Groups

  • •Six electron groups point toward the corners of an octahedron, with all bond angles equal to 90°.
  • •Sulfur hexafluoride (SF₆) is the canonical example, with all six positions filled by bonding pairs.

About this Study Pack

Created by Kibin to help students review key concepts, prepare for exams, and study more effectively. This Study Pack was checked for accuracy and curriculum alignment using authoritative educational sources. See sources below.

Sources

More in AP Chemistry

See all topics →

Browse other courses

See all courses →