The d block:
The d block consists of three horizontal series in periods 4, 5 & 6
10 elements in each series
Chemistry is “different” from other elements
Special electronic configurations important
Differences within a group in the d block are less sharp than in s & p block
Similarities across a period are greater
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Electronic Configuration
Across the 1st row of the d block (Sc to Zn) each element
has 1 more electron and 1 more proton
Each “additional” electron enters the 3d sub-shell
The core configuration for all the period 4 transition elements is that of Ar
1s22s22p63s23p6
1s
2s
3s
4s
2p
3p
3d
Energy
Ar
1s2 2s2 2p6 3s2 3p6
4p
1s
2s
3s
4s
2p
3p
3d
Energy
Sc
1s2 2s2 2p6 3s2 3p6 3d1 4s2
4p
Chromium and Copper
Cr and Cu don’t fit the pattern of building up the 3d sub-shell, why?
In the ground state electrons are always arranged to give lowest total energy
Electrons are negatively charged and repel each other
Lower total energy is obtained with e- singly in orbitals rather than if they are paired in an orbital
Energies of 3d and 4s orbitals very close together in Period 4
Chromium and Copper
At Cr
Orbital energies such that putting one e- into each 3d and 4s orbital gives lower energy than having 2 e- in the 4s orbital
At Cu
Putting 2 e- into the 4s orbital would give a higher energy than filling the 3d orbitals
1s
2s
3s
4s
2p
3p
3d
Energy
Cr
1s2 2s2 2p6 3s2 3p6 3d5 4s1
4p
1s
2s
3s
4s
2p
3p
3d
Energy
Cu
1s2 2s2 2p6 3s2 3p6 3d10 4s1
4p
What is a transition metal?
Transition metals [TM’s] have characteristic properties
e.g. coloured compounds, variable oxidation states
These are due to presence of an inner incomplete d sub-shell
Electrons from both inner d sub-shell and outer s sub-shell can be involved in compound formation
What is a transition metal?
Not all d block elements have incomplete d sub-shells
e.g. Zn has e.c. of [Ar]3d104s2, the Zn2+ ion ([Ar] 3d10) is not a typical TM ion
Similarly Sc forms Sc3+ which has the stable e.c of Ar. Sc3+ has no 3d electrons
What is a transition metal?
For this reason, a transition metal is defined as being an element which forms at least one ion with a partially filled sub-shell of d electrons.
In period 4 only Ti-Cu are TM’s!
Note that when d block elements form ions the s electrons are lost first
What are TM’s like?
TM’s are metals
They are similar to each other but different from s block metals eg Na and Mg
Properties of TM’s
Dense metals
Have high Tm and Tb
Tend to be hard and durable
Have high tensile strength
Have good mechanical properties
What are TM’s like?
Properties derive from strong metallic bonding
TM’s can release e- into the pool of mobile electrons from both outer and inner shells
Strong metallic bonds formed between the mobile pool and the +ve metal ions
Enables widespread use of TMs!
Alloys very important: inhibits slip in crystal lattice usually results in increased hardness and reduced malleability

Effect of Alloying on TM’s
TM Chemical Properties
Typical chemical properties of the TM’s are
Formation of compounds in a variety of oxidation states
Catalytic activity of the elements and their compounds
Strong tendency to form complexes
See CI 11.6
Formation of coloured compounds
See CI 11.6

Variable Oxidation States
TM’s show a great variety of oxidation states cf s block metals
If compare successive ionisation enthalpies (Hi) for Ca and V as follows
M(g)  M+(g) + e- Hi(1)
M+(g)  M2+(g) + e- Hi(2)
M2+(g)  M3+(g) + e- Hi(3)
M3+(g)  M4+(g) + e- Hi(4)
Hi for Ca and V
Hi for Ca and V
Both Ca & V always lose the 4s electrons
For Ca
Hi(1) & Hi(2) relatively low as corresponds to removing outer 4s e-
Sharp increase in Hi(3) & Hi(4) cf Hi(2) due to difficulty in removing 3p e-
For Sc
Gradual increase from Hi(1) to Hi(4) as removing 4s then 3d e-
Oxidation States of TM’s
In the following table
Most important OS’s in boxes
OS = +1 only important for Cu
In all others sum of Hi(1) + Hi(2) low enough for 2e- to be removed
OS = +2, where 4s e- lost shown by all except for Sc and Ti
OS = +3, shown by all except Zn
Oxidation States of TM’s
Oxidation States of TM’s
No of OS’s shown by an element increases from Sc to Mn
In each of these elements highest OS is equal to no. of 3d and 4s e-
After Mn decrease in no. of OS’s shown by an element
Highest OS shown becomes lower and less stable
Seems increasing nuclear charge binds 3d e- more strongly, hence harder to remove
Oxidation States of TM’s
In general
Lower OS’s found in simple ionic compounds
E.g. compounds containing Cr3+, Mn2+, Fe3+, Cu2+ ions
TM’s in higher OS’s usually covalently bound to electronegative element such as O or F
E.g VO3-, vanadate(V) ion; MnO4-, manganate(VII) ion
Simple ions with high OS’s such as V5+ & Mn7+ are not formed
Stability of OS’s
Change from one OS to another is a redox reaction
Relative stability of different OS’s can be predicted by looking at Standard Electrode Potentials
E values

Stability of OS’s
General trends
Higher OS’s become less stable relative to lower ones on moving from left to right across the series
Compounds containing TM’s in high OS’s tend to be oxidising agents e.g MnO4-
Compounds with TM’s in low OS’s are often reducing agents e.g V2+ & Fe2+
Stability of OS’s
General trends (continued)
Relative stability of +2 state with respect to +3 state increases across the series
For compounds early in the series, +2 state highly reducing
E.g. V2+(aq) & Cr2+(aq) strong reducing agents
Later in series +2 stable, +3 state highly oxidising
E.g. Co3+ is a strong oxidising agent, Ni3+ & Cu3+ do not exist in aqueous solution.
Catalytic Activity
TM’s and their compounds effective and important catalysts
Industrially and biologically!!
The “people in the know” believe
catalysts provide reaction pathway with lower EA than uncatalysed reaction (see CI 10.5)
Once again,
availability of 3d and 4s e-
ability to change OS
among factors which make TM’s such good catalysts
Heterogeneous Catalysis
Catalyst in different phase from reactants
Usually means solid TM catalyst with reactants in liquid or gas phases
TM’s can
use the 3d and 4s e- of atoms on metal surface to from weak bonds to the reactants.
Once reaction has occurred on TM surface, these bonds can break to release products
Important example is hydrogenation of alkenes using Ni or Pt catalyst
Heterogeneous Catalysis
Homogeneous Catalysis
Catalyst in same phase as reactants
Usually means reaction takes place in aqueous phase
Catalyst aqueous TM ion
Usually involves
TM ion forming intermediate compound with ome or more of the reactants
Intermediate then breaks down to form products
Homogeneous Catalysis
Above reaction is that used in Activity SS5.2
2,3-dihydroxybutanoate ion with hydrogen peroxide
Reaction catalysed by Co2+

Suggested Mechanism
REACTANTS
H2O2 +
-O2CCH(OH)CH(OH)C02-
Co2+ (pink)
INTERMEDIATE
containing
Co3+ (green)
PRODUCTS
CO2, methanoate, H2O
Co2+ (pink)