Chem1000A
Spring 2005
Assignment 5 - Solutions
Two or three questions will be marked from each assignment.
DUE ON Feb. 15, 2005 (Tuesday) 1:00 PM
To be dropped off at my office (E860)
1. (a) Draw Lewis structures of the following molecules. (b) Specify electron-pair geometries and
molecular geometries of the following molecules according the VSEPR model. (c) Indicate the bond
dipole moments and the overall molecular dipole moments (if the molecule is polar). Specify whether
the molecule is polar or non-polar. NOTE: In contrast to the book, we use the convention that
THE DIPOLE ARROW POINTS TOWARDS THE NEGATIVE SIDE OF THE DIPOLE
AND HAS A + ON THE POSITIVE SIDE: +
(i) ClO2(ii) XeO4
(iii) BrF4(iv) NO2F
(v) SeF4
(vi) SF3+
(vii) OH2
(viii) OF2
(ix) CFCl3
(x) XeF2
(xi) SF5(xii) XeO3F2
(xiii) PO2F2Due to the nature of the drawing program I used, I omitted the (+) – part of the bond dipole moment
arrow (I included it correctly for the overall dipole). Your hand-written answer should still the
correct dipole arrow( +
) in all cases.
(i)
..
: Cl
:O
.. :
-
O
.. :
..
: Cl
:O
..
..
O
.. :-
+
.. ..
Cl
O
O
electron-pair geometry: tetrahedral (SN = 4)
molecular geometry: bent(the two ClO bonds are equivalent)
polar molecule: molecular dipole moment is pointing towards the side of the oxygens, away from Cl
(ii)
:O :
Xe
:O
..
O
.. :
O
.. :
electron-pair geometry: tetrahedral
(SN =4)
molecular geometry: tetrahedral
bond dipole moments cancel each other,
therefore, no mol. dipole moment
XeO4 is non-polar
(iii)
..
.. - .. F
.. :..
:F
.. .. Br
..F:
..
:F
..
electron-pair geometry: octahedra (SN = 6)
molecular geometry: square planar
(lone pairs on opposite sides of the plane)
bond dipole moments cancel each other,
therefore, no molecular dipole moment
BrF4- is non-polar
1-4
(iv)
..
:..F N
..
O:
..
:..F N
:O :
.. -
.. : O:
(v)
..
: F : ..
F.. :
: Se ..
F.. :
: F:
..
O
F N
O
O
.. :
+
electron-pair geometry: trigonal planar
(both NO bonds are equivalent due to resonance)
molecular geometry: trigonal planar
The bond dipole moment of NF is significantly
larger than that of the NO bonds, hence,
the NF dipole is only partially compensated by the
NO dipoles. The resulting molecular dipole moment
points in the direction of the fluorine.
NOF2 is polar.
+
electron-pair geometry: trigonal bipyramidal
(lone pair goes into the equatorial position)
molecular geometry: see saw
the axial SeF dipoles will cancel each other.
The equatorial SeF dipoles will add up to a
molecular dipole moment, pointing to the side
of the two equatorial fluorines.
SeF4 is polar.
(vi)
(vii)
+
.. +
..
S ..
F
:..
F
.. :
:F :
..
.. ..
O
H
electron-pair geometry: tetrahedral
molecular geometry: trigonal pyramidal
The SF bond dipole moments point have all
a component pointing down.
SF3+ is polar.
electron-pair geometry: tetrahedral
molecular geometry: bent
The OH bond dipole moments point towards O.
H2O is polar.
(ix)
(viii)
.. ..
O
: F : : F:
..
..
+
electron-pair geometry: tetrahedral
molecular geometry: bent
The OF bond dipole moments point towards F.
F2O is polar.
2-4
+
H
..
:F :
..
:Cl
..
:Cl :
..
..
Cl
.. :
+
electron-pair geometry: tetrahedral
molecular geometry: tetrahedral
The CCl bond dipole moments are smaller than
that of the CF bond. Hence, the overall molecular
dipole moment points in the direction of F.
CFCl3 is polar.
(x)
(xi)
.. .. .. ..
:F
F:
.. Xe
.. ..
..
:..
F..
:..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
XeF2 is non-polar
..
O
..
+
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
SF5- is a polar molecule.
..
:F:
(xii)
..
: F : ..
F
....:
S
F
.. :
..
-
..
O
..
Xe ..
O
..
: F:
..
(xiii)
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, XeO3F2 is non-polar.
- ..
:O :
..
:..F
..
O:
P
..
..F:
..
:O
..
:..F
.. :O :
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
PO2F2- is polar.
2. Give the chemical formulae for the following ionic compounds and specify which ions are present.
(a) calcium perchlorate
Ca2+ and ClO4- ion: Ca(ClO4)2
(b) barium phosphate
Ba2+ and PO43- ion: Ba3(PO4)2
(c) aluminum hydrogen sulfate
Al3+ and HSO4- ion: Al(HSO4)3
(d) lithium chlorite
Li+ and ClO2- ion: LiClO2
3-4
(e) ammonium nitrate
NH4+ and NO3- ion: NH4NO3
(f) aluminum sulfate
Al3+ and SO42- ion: Al2(SO4)3
(g) calcium chloride
Ca2+ and Cl- ion: CaCl2
(h) ammonium hypochlorite
NH4+ and ClO- ion: NH4ClO
4-4