CHAPTER 23. The Transition Metals (TM )
TM = metals having partiallyfilled d or f shells as the elements or in common oxidation states.
We shall look only at the d metals.
Orbital energies: 1s2s2p3s3p4s3d4p5s4d5p6s4f5d6p7s5f6d..
2 2 6 2 6
[Ar] = 1s 2s 2p 3s 3p
1 TM Series: [Ar] 4s 3d (the “condensed” configuration)
nd 2 n
2 TM Series: [Kr] 5s 4d
3 TM series: [Xe] 6s 5d 2 n
Group number = sum of outer s and d electrons
∴ Fe : group 8 : [Ar] 4s 3d 2 6
Table 22.1. Filling of s and d orbitals
note stability of halffilled (Cr) and filled (Cu) d
**When TM’s form M ions (i.e. higher
oxidation state than the element), the s/d
energies switch position (now 3d below 4s)
and remaining electrons all go in d
The outer electron confign (“partial” configuration)
thus now is:
Ni metal (= Ni ) = 4s 3d but Ni = 3d , Ni = 9 2+
3d , etc
0 2 9 + 10 2+ 9
Ag metal = (Ag ) = 5s 4d but Ag = 4d , Ag = 4d , etc
2+ 10 3+ 6 4+ 3
Similarly: Cd = 4d Ir = 5d Mn = 3d etc
2+ 3+ 2+ 2+ 3+
Rh = W = Cu = Zr = Co =
General properties of TM’s.
1. all are metals
2. all are solids at 298 K, except mercury (Hg)
1 3. all are stable in multiple oxidation states except groups 3 and 12
4. redox reactions are common
5. partiallyfilled dshell gives colored species
6. partiallyfilled dshell often results in unpaired electrons.
7. size of M ions down a group: 3d 4d Cr > Cr
Therefore, oxide acidity increases with oxidation state.
Let’s compare the Cr oxides to see how this affects properties.
Chromium(II) Oxide (CrO i.e. Cr ): is mainly ionic and basic, typical of a metal oxide
(i.e. like Na O2or CaO). Therefore, reacts with acids but not bases.
CrO (s) + 2 H (aq) → Cr (aq) + H O (l)
Chromium(III) Oxide (Cr O i.e. Cr ): a2pho3 ric (i.e. similar to Al O ) 2 3
can act as an acid: Cr 2 (3) + 2OH(aq) + 3H O(l) → 22r(OH) 4
or as a base: Cr O (s2 +36 H (aq) → 2 Cr (aq) + H O(l) 2
Chromium(VI) Oxide (CrO i.e. Cr ): is covalent and acidic. Cr ion has too high a 6+
charge to exist as the ion, and thus shares electrons (covalent bonding). Like SO (covalent) 3
rather than CaO (ionic).
CrO (3) + H O(l2 → H CrO (a2) (4hromic acid)
Note: very similar behavior to SO , which g3ves H SO (sulfuric 2cid)4in water.
On deprotonation, gives CrO = chromate ion. Compare: SO = sulfate ion. 2
in acid: 2 CrO (4q) + 2 H (aq) → Cr O (aq) +2H 7 (l) 2
3 yellow orange
in base: Cr O (aq) + OH (aq) → 2 CrO (aq) + H (aq) +
2 7 4
2 2 6+ 3+
CrO 4nd Cr O ar2 s7rong oxidizing agents, each Cr picking up 3 e and converting to Cr .
2 + 3+
CrO (4q) + 14H (aq) + 6e → 2Cr (aq) + 7H O 2 E˚=1.33V high!
Strong enough to oxidize stable ions such as NH to N (g) i.e. nitrogen(III) oxidized to
e.g. decomposition of the ammonium dichromate salt
(NH ) Cr O (s) → Cr O (s) + N (g) + 4H O
4 2 2 7 2 3 2 2
halfreactions: 2 Cr + 6 e → 2 Cr 3+
2 NH 4→ N (g) 2 8 H + 6 e
Manganese (Group 7)
Mn: [Ar] 4s 3d 5
2+ 5 3+ 4 4+ 3 7+ 0
most important oxid states: Mn (d ), Mn (d ), Mn (d ), Mn (d )
ionic character of bonds decreases with increasing oxidation state. We see this in the oxides, for
MnO: ionic and basic (like NaCl or CaO)
Mn O 2 3 amphoteric
MnO :in2oluble – no acid/base reactions.
Mn O 2 7 acidic and covalent
Mn O2 (7) + H O (l) 2→ HMnO = permanganic 4cid (compare HClO = 4
HMnO is 4oo unstable for everyday use, but its salts are much more stable. e.g. KMnO = 4
3+ 4+ 7+
Mn , Mn , and Mn are all good oxidizing agents
e.g. MnO (aq) + 4H (aq) + 3e → MnO (s) + 2H O (l) E˚=1.68V
4 2 2