Chem1000A Spring 2007 Practice Assignment 6 - Answers

(x) (xi)
..
: F Xe .. F:
.. .. ..
.. ..
electron-pair geometry: trigonal bipyramidal
the three lone pairs are located in
the equatorial positions, therefore:
molecular geometry: linear
the XeF dipole moments cancel each other
XeF 2 is non-polar
(xii)
..
O..
..
: F :
Xe
..
F : :
..
O..
..
O..
electron-pair geometry: trigonal bipyramidal
molecular geometry: trigonal bipyramidal
the double-bond domains are located in the
equatorial plane.
The XeF bond dipole moments cancel each other.
The three XeO dipole moments cancel each other,
too. Therefore, XeO 3 F 2 is non-polar.
4-5
+
: ..
.. F
: F
..
..
..
: F : ..
F..
.. :
S F..
:
..
-
electron-pair geometry: octahedral
molecular geometry: square pyramidal
the four SF bond dipole moments of the
equatorial fluorines will cancel each other
the axial SF dipole remains
SF 5 - is a polar molecule.
(xiii)
:
..
.. :
..
O O
.. F
P
F
:
..
.. :
..
- ..
: :
..
:
..
: O
.. -
: O:
.. F
P
F
electron-pair geometry: tetrahedral
molecular geometry: tetrahedral
PF bond dipole moments are larger than those
of the PO bond, therefore, a small residual
dipole moment in the direction of the F's remains
PO 2 F 2 - is polar.
4. Determine the oxidation states in the following sulfur compounds (only one resonance structure is
given). Use the original definition of the oxidation state (by cleaving bonds). For (b) and (c),
distinguish between the oxidation states for individual sulfur atoms and an average oxidation state for
sulfur (i.e., the average of the two – or more – values). You would obtain these average oxidation
states if you use the ‘simple rules’, that are usually used for oxidation states.
(a) peroxodisulfate: S2O8 2-
+