Untitled - Kelly Walsh High School

154 CHEMISTRY FOR THE UTTERLY CONFUSED
double bond. This gives a total of three. Three pairs give a trigonal planar
electron-group geometry, they also imply an sp 2 hybridization. A trigonal planar
electron-group geometry with one lone pair leaves us with a bent molecular
geometry. As a bent species, with atoms of differing electronegativities, it is
polar.
If we examine the other central atom, the oxygen with the attached hydrogen,
we observe the presence of two lone pairs and two bonds. The presence of these
pairs and bonds, which total four, means that the electron-group geometry is
tetrahedral. This arrangement has sp 3 hybridization. Since there are two lone
pairs, the molecular geometry is bent.
An examination of the xenon tetrafluoride structure shows that the central
atom, the xenon, has four bonds and two lone pairs. Six groups lead to an octahedral
electron-group geometry. In this case, the hybridization is sp 3 d 2 . There
are two lone pairs; so, the molecular geometry is square planar. This geometry
indicates that even though the bonds are polar covalent, their arrangement
leads to a nonpolar molecule.
The number of pairs of electrons surrounding the central atom primarily determines
the shape of a molecule, its molecular geometry. You may determine this
by first determining the Lewis structure of the molecule and then applying
VSEPR theory. VSEPR theory assumes that the electron pairs surrounding the
central atom will assume a geometry that minimizes the repulsion between
them. Another method of determining the molecular shape is to use valance
bond theory in which individual atomic orbitals blend to form hybrid orbitals.
Molecular orbital theory is a way of describing covalent bonding in a molecule
in terms of the combining of atomic orbitals to form molecular orbitals.
1. What does the abbreviation VSEPR stand for?
2. Reconstruct Figure 10-1.
3. Determine the molecular geometries about the central atom for each of the
following.
a. H2S b. Cl2O c. BF3 4. Determine the molecular geometries about the central atom for each of the
following.
a. SF4 b. XeF2 c. NH4+ 5. Determine the molecular geometries about the central atom for each of the
following.
a. SF6 b. CS2 6. Determine the hybridization of the central atom for each of the following.
a. H2S b. Cl2O c. BF3