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Make a model of an ammonia molecule using one blue ball and attaching three white balls to it using the rigid gray pegs. Draw a diagram of the model and a Lewis structure of ammonia below.
This section explores how we predict the molecular and electron-pair shapes of molecules using the VSEPR (Valence Shell Electron Pair Repulsion) theory. We will first go over what VSEPR theory is and how it defines an electron-pair geometry and a molecular geometry.
Explore molecule shapes by building molecules in 3D! How does molecule shape change with different numbers of bonds and electron pairs? Find out by adding single, double or triple bonds and lone pairs to the central atom. Then, compare the model to real molecules!
Ammonia has 4 regions of electron density around the central nitrogen atom (3 bonds and one lone pair). These are arranged in a tetrahedral shape. The resulting molecular shape is trigonal pyramidal with H-N-H angles of 106.7°.
You can investigate the structure of molecules, or of model shapes using VSEPR. By placing the cursor on any of the non central atoms or lone pairs you can rotate the molecules. You can add atoms and lone pairs to make any of VSEPR shapes
When a molecule or polyatomic ion has only one central atom, the molecular structure completely describes the shape of the molecule. Larger molecules do not have a single central atom, but are connected by a chain of interior atoms that each possess a “local” geometry.
Valence shell electron pair repulsion (VSEPR) theory is a model in chemistry used to predict the shape of individual molecules based upon the extent of electron-pair electrostatic repulsion. It is also named Gillespie-Nyholm* theory after its two main developers.
