Transcript the second and third row metals

Inorganic Chemistry B
Chapter 23
d-Block metal chemistry:
the second and third row metals
Dr. Said El-Kurdi
1
23.1 Introduction
Dr. Said El-Kurdi
2
The abundances of some of the heavier metals are very low,
e.g. Os, 1104 ppm and Ir, 6106 ppm; Tc does not occur
naturally
Yttrium and lanthanum are similar to the lanthanoids and
occur with them in nature.
Zirconium is the next most abundant d-block metal in the
Earth’s crust after Fe, Ti and Mn
Zirconium and hafnium occur naturally together and are hard
to separate. Hf is rarer than Zr, 5.3 and 190 ppm, respectively,
of the Earth’s crust.
Dr. Said El-Kurdi
3
Very pure metals can be obtained by zone refining
Beginning with a polycrystalline rod, a small zone (which lies
perpendicular to the direction of the rod) is melted.
The focus-point of the zone is gradually moved along the
length of the rod; under carefully controlled conditions,
cooling, which takes place behind the melt-zone, produces
single crystals while impurities migrate along the rod with
the molten material.
Dr. Said El-Kurdi
4
Niobium (formerly known as columbium) and tantalum occur
together in the mineral columbite (Fe,Mn)(Nb,Ta)2O6
molybdenum and tungsten compounds
isomorphous, the elements occur separately.
are
Technetium is an artificial element, available as
particle emitter
usually
99Tc
(a -
Rhenium is rare and occurs in small amounts in Mo ores.
The platinum-group metals (ruthenium Ru, Osmium Os,
Rhodium Rh, iridium Ir, Pd and Pt) are rare and expensive,
and occur together either native or in sulfide ores of Cu and
Ni.
Dr. Said El-Kurdi
5
Silver and gold occur native, and in sulfide, arsenide and
telluride ores, e.g. argentite (Ag2S)
Cadmium occurs as the rare mineral greenockite (CdS), but the
metal is isolated almost entirely from zinc ores, CdS occurring
(<0.5%) in ZnS.
Cadmium has a relatively low melting point (594 K) and is used
as an alloying agent in low-melting alloys.
The main use of cadmium is in NiCd batteries
Dr. Said El-Kurdi
6
The symbol Hg is derived from hydrargyrum (Latin) meaning
‘liquid silver’. The major source of mercury is cinnabar (HgS),
from which the metal is extracted by roasting in air
23.3 Physical properties
The electronic configurations of the ground state M(g) atoms
change rather irregularly with increasing atomic number more
so than for the first row metals
the nd and (n+1)s atomic orbitals are closer in energy for
n = 4 or 5 than for n = 3
Dr. Said El-Kurdi
7
Dr. Said El-Kurdi
8
Dr. Said El-Kurdi
9
with the exception of Hg (group 12), the heavier metals have
higher values of aHo than their first row congeners. This is a
consequence of the greater spatial extent of d orbitals with
an increase in principal quantum number, and greater
orbital overlap. 5d–5d > 4d–4d > 3d–3d.
Dr. Said El-Kurdi
10
The heavier metals exhibit many more compounds containing
M  M bonds.
In general, the stability of high oxidation states increases for
a given triad in the sequence first row  second row < third
row metals.
 easier promotion of electrons for the 5d metals
compared with 4d or 3d metals;
 better orbital overlap for 5d orbitals (or those with 5d
character) than for 4d or 3d orbitals.
Dr. Said El-Kurdi
11
Relativistic effects
If Einstein’s theory of relativity is combined with quantum
mechanics, in which case they are attributed to relativistic
effects.
According to the theory of relativity, the mass m of a particle
increases from its rest mass m0 when its velocity v
approaches the speed of light, c, and m is then given by the
equation:
Dr. Said El-Kurdi
12
For a one-electron system, the Bohr model of the atom leads
to the velocity of the electron being expressed by the
equation:
where Z = atomic number, e = charge on the electron, 0 =
permittivity of a vacuum, h = Planck constant
For n = 1 and Z = 1, v/c is only (1/137)
but for Z = 80, v/c = 0.58 leading to m = 1.2m0. Since the
radius of the Bohr orbit is given by the equation
Dr. Said El-Kurdi
13
the increase in m results in an approximately 20% contraction
of the radius of the 1s (n = 1) orbital; this is called relativistic
contraction.
Other s orbitals are affected in a similar way and as a
consequence, when Z is high, s orbitals have diminished
overlap with orbitals of other atoms.
p orbitals (which have a low electron density near to the
nucleus) are less affected.
d orbitals (which are more effectively screened from the
nuclear charge by the contracted s and p orbitals) undergo a
relativistic expansion; a similar argument applies to f
orbitals.
Dr. Said El-Kurdi
14
The relativistic contraction of the s orbitals means that for an
atom of high atomic number, there is an extra energy of
attraction between s electrons and the nucleus.
Dr. Said El-Kurdi
15
Effects of the lanthanoid contraction
pairs of metals in a triad (Zr and Hf, Nb and Ta etc.) are of
similar radii. This is due to the lanthanoid contraction: the
steady decrease in size along the series of lanthanoid
metals Ce–Lu which lie between La and Hf in the third row
of the d-block.
This observation is due to the presence of a filled 4f
level
the shielding of one 4f electron by another is less than for
one d electron by another, and as the nuclear charge
increases from La to Lu, there is a fairly regular decrease in
the size of the 4f n sub-shell.
Dr. Said El-Kurdi
16
Coordination numbers
Consistent with the increase in size in going from a first row
to later metals in a triad, the heavier metals tend to show
higher coordination numbers.
23.4 Group 3: yttrium
In the coordination chemistry of Y3+, coordination numbers
of 6 to 9 are usual.
The Y3+ ion is ‘hard’ and in its complexes favors hard N- and
O- donors
Dr. Said El-Kurdi
17
23.5 Group 4: zirconium and hafnium
The Lewis acidity of the halides is seen in the formation of
complexes such as HfCl42L (L = NMe3, THF)
23.6 Group 5: niobium and tantalum
The properties of Nb and Ta (and of pairs of corresponding
compounds) are similar. At high temperatures, both are
attacked by O2 (equation 23.20) and the halogens (equation
23.21) and combine with most non-metals.
Dr. Said El-Kurdi
18
The halides NbF5, TaF5, NbCl5 and TaCl5 are useful starting
materials in the chemistry of these metals.
23.7 Group 6: molybdenum and tungsten
Octahedral geometries are common for complexes of Mo(IV)
and W(IV),
The salt K4[Mo(CN)8]2H2O was the first example (in 1939)
of an 8-coordinate (dodecahedral) complex.
However, studies on a range of salts of [Mo(CN)8]4 and
[W(CN)8]4 reveal cation dependence, both dodecahedral
and square antiprismatic anions being found
Dr. Said El-Kurdi
19
23.8 Group 7: technetium and rhenium
Dr. Said El-Kurdi
20
23.9 Group 8: ruthenium and osmium
Like all platinum-group metals, Ru and Os are relatively noble.
Osmium powder reacts slowly with O2 at 298K to give the
volatile OsO4
Dr. Said El-Kurdi
21
Dr. Said El-Kurdi
22