Small Molecule Geometry
VSEPR Theory
Atoms and electrons within a molecule will repel one another. Therefore, scientists developed the Valence Shell Electron Pair Repulsion (VSEPR) Theory: In a small molecule, the pairs of valence electrons are arranged as far apart from each other as possible. In other words, bonded atoms and unshared pairs of electrons take up room around the central atom, and try to get as far away from one another as possible. This theory does not work for all elements (esp. the transition metals), but is a good basis for understanding
Molecular Geometry
With small molecules (both ionic and covalent), there are five typical shapes that exist. Most small molecules can be classified as one of the following shapes:
Atoms and electrons within a molecule will repel one another. Therefore, scientists developed the Valence Shell Electron Pair Repulsion (VSEPR) Theory: In a small molecule, the pairs of valence electrons are arranged as far apart from each other as possible. In other words, bonded atoms and unshared pairs of electrons take up room around the central atom, and try to get as far away from one another as possible. This theory does not work for all elements (esp. the transition metals), but is a good basis for understanding
Molecular Geometry
With small molecules (both ionic and covalent), there are five typical shapes that exist. Most small molecules can be classified as one of the following shapes:
4) Pyramidal:
Same as tetrahedral, but with one pair of unshared electrons. This electron pair takes the place of one of the bonds of a tetrahedral molecule. A pyramidal molecule typically has a central atom with three atoms bonded and an unshared pair of electrons. The unshared pair of electrons take up a little more room (have a greater repulsion force) than a bonded atom, so the bond angle is reduced to 107 degrees. |
5) Bent:
Same as tetrahedral, but with two pairs of unshared electrons. These electron pairs take the place of two of the bonds of a tetrahedral. A bent molecule has a central atom with two atoms attached and 2 unshared pairs of electrons. These 2 unshared electron pairs take up still a little more room (have an even greater repulsion force) than a bonded atom, so the bond angle is reduced to 105 degrees. |
The following diagram summarizes the information above: