Transition metal chemistry
1. What defines a transition metal?
2. Write electron configurations for the following atoms and ions.
a) Sc
b) V
c) Cr
d) Fe
e) Cu
f) Sc3+
g) Mn2+
h) Ni2+
i) Cu2+
j) Cu+
k) Zn2+
3. Which of the ions above are not considered transition metal ions and why not?
4. Why do so many different oxidation states exist within the transition metals?
5. Suggest a structure for the following complex ions and draw them. Work out the
overall charge on the complex ion.
a) [Cu(II)(H2O)6]
b) [Cu(II)(NH3)4(H2O)2]
c) [Cu(II)Cl4]
d) [Fe(III)(C2O4)3]
e) [Ni(II)(NH2CH2CH2NH2)3]
6.
a) What type bonding exists between the ligand and the metal? How does it
arise?
b) Which of the ligands in the above complexes are monodendate and which are
bidentate?
c) Why are transition metals such good catalysts?
d) Explain why many transition metal complexes are intensely coloured. Use the
bright blue complex [Cu(II)(NH3)4(H2O)2]2+ as an example showing the
arrangement of d electrons in the metal ion.
e) [Cu(II)(NH3)4(H2O)2]2+
↔
[Cu(II)(H2O)6] 2+
↔
[Cu(II)Cl4]2-
What do you need to add to push the equilibrium to the left or right in the above
reactions?
7.
i) Write balanced equations and describe what happens when excess sodium
hydroxide is added to solutions of
a) Cr3+
b) Fe2+
c) Fe3+
b) Cu2+
ii) Name an important industrial (catalytic) application for transition metals.
iii) Name an important biological role for transition metals.
1. A transition metal is one which forms an ion with a partially filled d sub-shell.
Sc
V
Cr
Fe
Cu
Sc3+
Mn2+
Ni2+
Cu2+
Cu+
Zn2+
1s22s22p63s23p63d14s2
1s22s22p63s23p63d34s2
1s22s22p63s23p63d54s1
1s22s22p63s23p63d64s2
1s22s22p63s23p63d104s1
1s22s22p63s23p6
1s22s22p63s23p63d5
1s22s22p63s23p63d8
1s22s22p63s23p63d9
1s22s22p63s23p63d10
1s22s22p63s23p63d10
2.
a)
b)
c)
d)
e)
f)
g)
h)
i)
j)
k)
3.
Sc3+, Cu+, Zn2+
4.
There is only a small difference in the ionisation energy for the removal of
sequential d sub-shell electrons; therefore it is possible to remove different amounts of
electrons quite easily. In the s-block the barrier of a new shell is reached quickly limiting
oxidation states to +1 and +2.
5.
a) [Cu(II)(H2O)6]
–
b) [Cu(II)(NH3)4(H2O)2]
2+ , octahedral
–
2+ , octahedral
c) [Cu(II)Cl4]
–
2- , tetrahedral
d) [Fe(III)(C2O4)3]
-
3- , octahedral
e) [Ni(II)(NH2CH2CH2NH2)3]
-
2+ , octahedral
6.
a) A dative or coordinate bond. The ligand donates a lone pair into the
empty d-orbitals on the metal ion.
b)
H2O, NH3, Clmonodentate
C2O42-, NH2CH2CH2NH2 bidentate
c) They accept lone pairs from the reactant molecules to form intermediate
complexes. These modify electron arrangements in the reactants, making it
easier to break bonds (lowers Ea). The variable oxidation states of transition
metals also facilitate redox reactions.
d) The partially filled d-orbitals of similar energy levels are split into two
different energy levels. 2 orbitals have a higher energy level than the other 3 (if
octahedral). The lower energy orbitals will be filled sequentially and at least one
of the higher energy pair will be empty or half full. Electrons can be promoted to
this higher level from the lower one absorbing a small amount of energy (hf) to do
so. This energy happens to correspond to light in the visible region and so some
visible light is absorbed and the rest reflected making the substance appear
coloured.
Cu2+ 3d9
→
↑↓ ↑
↑↓ ↑↓ ↑↓
e)
add water →
add Cl- →
Cu(II)(NH3)4(H2O)2]2+
↔
[Cu(II)(H2O)6] 2+
↔
[Cu(II)Cl4]2← add NH3
← add water
Cr3+(aq)
+
3OH-(aq)
→
Cr(OH)3(s)
green solid
Cr(OH)3(s)
+
3OH-(aq)
→
Cr(OH)-4(aq)
green solution
b)
Fe2+(aq)
+
2OH-(aq)
→
Fe(OH)2(s)
blue/green solid
c)
Fe3+(aq)
+
3OH-(aq)
→
Fe(OH)3(s)
red/brown solid
b)
Cu2++(aq)
+
2OH-(aq)
→
Cr(OH)2(s)
blue solid
7. (i) a)
(ii)
Iron – Haber process
Vanadium – Contact process
Nickel – Hydrogenation
Titanium – Ziegler Natta
(iii)
Iron – haemoglobin
Cobalt – vitamin B12
Molybenum – nitrogenase
Copper - cytochromes