課程名稱︰化學鍵
課程教師：金必耀/王瑜
開課系所︰化學系
考試時間︰2004/04/21
課程性質︰選修
Chemical Structure and Bonding
2004. 4.21
1.Show that there exists for the carbon monoxide molecule(CO);
(a)A Lewis structure where the octet rule is obeyed at each atom but which
contains a separation of charge, and
(b)a Lewis structure which does not have a separation of charge but does not
obey the octet rule. (8%)
2.Give the electronic configuration for platinum (Pt,Z=78) which is in accord
with Klechkowsky's rule. Knowing that the 6s and 5d levels are very close
in energy, suggest two other configurations which should be close in energy
to this. (8%)
3.Consider the distortion of a equilateral triangular H3 (I) to an isosceles
triangular geometry (II). With reference to the equilateral structures the
isosceles triangular geometry is generated by elonggation of the distance
Ha-Hb and Hb-Hc.
Hb Hb
‧ ‧
╱╲ ──→ ∕﹨
Ha‧──‧Hc ∕ ﹨
Ha‧──‧Hc
I II
(a)Select a pair of fragments for construction of the MOs for both
geometries. (2%)
(b)Find a symmetry element which will allow a seperation of orbitals into
two sets, those symmetric and those antisymmetric with respect to this
operation. (2%)
(c)Construct the fragment orbital interaction diagram for both equilateral
and isosceles triangular H3. By analysis of the overlaps between the
interacting orbitals, what is the electronic differences between the two
geometries. (8%)
(d)Compare the form and relative energy of the molecular orbitals of these
two type of geometries. Show in particular that the degeneracy of the
orbitals in equilateral H3 is removed. (4%)
4.Consider the model tetrahedral system H2X2 in which the X atom only comes
with an s type orbital(sX).
H
﹨﹎X
∕◣
H X
(a)Suggest a fragmentation route for the construction of the molecular
orbitals. (2%)
(b)Choose two symmetry planes. (2%)
(c)Assuming that X is more electronegative than H
(i)on an energy diagram draw out the energies of the fragment orbitals.
Give their form in terms of the constituent AOs and their symmetry
with respect to the two planes you chose in (b).
(ii)Construct the MOs via interaction of the fragment orbitals.
(iii)Compare their composition and energy with those of the tetrahedral
H4 molecule. (8%)
(d)Repeat part (c) for the case where X is less electronegative than H.
(4%)
5.Construct the MOs of an octahedral H6. The six hydrogen atoms are assumed
to be located on six vertices of octahedron respectively.
H
│..H
H─┼─H
◤│
H H
(a)Suggest a fragmentation process for the molecule. (2%)
(b)Select three planes of symmetry and derive the symmetry properties of the
fragment orbitals with respective to these planes. (4%)
(c)Construct the fragment orbital interaction diagram. (6%)
(d)Give the form of the MOs you have derived. In particular show that the
MOs belonging to the same degenerate manifold can be constructed in such
a way that they have the same orbital shape but different orientation.
(8%)
6.Consider the effect of substitution on the molecular orbitals of an
octahedral H4X2:
X
│..H
H─┼─H
◤│
H X
in which the X atom only comes with an s type orbital (sX)
(a)Suggest a fragmentation route for the construction of the molecular
orbitals. (2%)
(b)Choose suitable symmetry planes. (2%)
(c)Assuming that X is more electronegative than H
(i)on an energy diagram draw out the energies of the fragment orbitals.
Give their form in terms of the constituent AOs and their symmetry
with respect to the two planes you chose in (b).
(ii)Construct the MOs via interaction of the fragment orbitals. (8%)
(d)Compare their composition and energy with those of the tetrahedral H6
molecule. (4%)
7.There is a different isomer for H4X2
X
│..H
H─┼─X
◤│
H H
(a)Suggest a fragmentation route for the construction of the molecular
orbitals. (2%)
(b)Choose suitable symmetry planes. (2%)
(c)Assuming that X is more electronegative than H
(i)on an energy diagram draw out the energies of the fragment orbitals.
Give their form in terms of the constituent AOs and their symmetry
with respect to the two planes you chose in (b).
(ii)Construct the MOs via interaction of the fragment orbitals. (8%)
(d)Compare their composition and energy with those of the tetrahedral H6
and trans-H4X2 molecule. (4%)
Total:104%
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