Electron groups around a central atom repel one another and arrange to minimize repulsion, determining molecular shape.
Practise Bonding & Molecular Structure All Bonding & Molecular Structure topics
The valence shell electron pair repulsion model predicts molecular shapes from the idea that electron groups around a central atom arrange themselves as far apart as possible. Electron groups include bonding pairs, lone pairs and multiple bonds, with each multiple bond counted as one region. Lone pairs repel more strongly than bonding pairs, so they compress the angles between bonds. The procedure is to draw the Lewis structure, count the electron groups around the central atom, choose the geometry that minimizes repulsion and then name the molecular shape by ignoring the lone pairs. VSEPR is simple yet predicts the shapes of most main-group molecules.
Key ideas: Method: count electron domains (bonded atoms plus lone pairs), choose the geometry from the number (2 linear, 3 trigonal planar, 4 tetrahedral, 5 trigonal bipyramidal, 6 octahedral), and place lone pairs where repulsion is least. Name the shape from atoms only. A double bond counts as one domain. Use the table of AXnEm notation to read off the answer.
Common mistakes and connections: Common errors are not counting lone pairs, counting every bond of a multiple bond as separate domains, and naming the electron geometry instead of molecular geometry. VSEPR gives approximate angles and fails for some heavy-element compounds. Connects to Lewis structures, hybridization, polarity and dipole moments.
Four electron groups around carbon repel each other and settle at the corners of a tetrahedron with H-C-H angles of 109.5 degrees. The interactive lesson shows this as a live animation or chart.
The four electron groups around nitrogen in NH3 point to a tetrahedron, but the molecular shape is trigonal pyramidal because one position holds a lone pair.
Electron groups around a central atom repel one another and arrange to minimize repulsion, determining molecular shape.
VSEPR Theory is a beginner topic in Bonding & Molecular Structure. It needs no earlier chemistry lessons and is a good starting point.
Study these earlier topics in Bonding & Molecular Structure first: Band Theory, Semiconductors, Doping.
The next topics in Bonding & Molecular Structure are Electron Domain Geometry and Molecular Geometry.
Yes. The interactive lesson includes a self-check question on VSEPR Theory, and the Bonding & Molecular Structure quiz draws on every topic in this area.
VSEPR Theory is topic 35 of 104 in Bonding & Molecular Structure.