Molecular Geometry MOLECULAR GEOMETRY VSEPR stands for Valence
- Slides: 8
Molecular Geometry
MOLECULAR GEOMETRY VSEPR stands for: Valence Shell Electron Pair Repulsion theory. Molecules form their shapes to minimize the repulsions of the electrons. • Most important factor in determining the shape of the molecule is the repulsion between electron pairs. *They get as far away from each other as possible!
VSEPR Charts • Use the Lewis Structure to determine the geometry of the molecule. • Focus only on the CENTRAL atom for all molecules! Count the number of electron regions. • Look for REGIONS WHERE ELECTRONS ARE FOUND rather than number of bonds. (Ex: Double and Triple bonds count as 1 region)
Lets look at Methane (CH 4). The molecule is really three dimensional, not planar and flat. H H C H H
When models are constructed, they show the bonds, but not the lone pairs of electrons. . . 109. 5° (109. 5°) 109. 5° (107°) . . 109. 5° (104. 5°)
Some Common Geometries
Structure Determination by VSEPR Water, H 2 O • 1) Looking at the central atom, • • how many regions are • • there? H O H 2 bond pairs 2 lone pairs • 2) How many bonded atoms? How many lone pairs? The electron pair geometry is TETRAHEDRAL The molecular geometry is BENT.
Structure Determination by VSEPR Ammonia, NH 3 The electron pair geometry is Tetrahedral , and the Geometry name is TRIGONAL PYRAMID.
