CHEM 1201 Lecture Notes - Valence Bond Theory, Molecular Geometry, Vsepr Theory
Document Summary
Lewis structure s gives atomic connectivity: they tell us which atoms are physically connected to which. The shape of a molecule is determined by its bond angles. The angles made by the lines joining the nuclei of the atoms in a molecule are the bond angles. Consider ccl4: all cl atoms are located at the vertices of a tetrahedron with the c at its center. Experimentally, we find all cl-c-cl bond angles are 109. 5o. Therefore, the m olecule, ccl4, cannot be planar. In order to predict molecular shape, we assume the valence electrons (lone pairs on atoms and bonding electrons) repel each other. Therefore, the molecule adopts whichever 3d geometry minimizes this repulsion. The valence electrons in a molecule are the bonding pairs of electrons as well as the lone pairs. The bonding pair of electrons occupies space between atoms. A nonbonding pair of electrons (or lone pair) defines an electron domain that is located principally on one atom.
