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Thursday, 28 January 2016

TRANSITION METALS

TRANSITION METALS
Illustrated by the elements:  Cr, Mn, Fe and Cu.

Summary
·      The d block elements in the fourth period contain the traditional metals - there are 10

·      all metallically bond, and are often hexagonally close packed. They form alloys eg steel, brass and bronze. These are of variable composition; and can be made to alter both physical (strength, malleability) and chemical properties (chemical reactivity, catalytic effect)

·      Have high melting points and boiling points, and are very strong and dense. This is because their metallic bonds are strong, with a large number of delocalised electrons (4s + some 3d) and radii are small

·      Radii are very similar and relatively small. This is because the nuclear charge is high and the 3 d electrons are diffuse and do not screen the valence electrons from this large charge.

·      they are not very reactive because  their ionisation energies are high compared to Groups I and II, this high IE again arises because of the large nuclear charge and small radii

·      They form compounds with ionic and covalent character and with variable oxidation states; The small highly charged cations have a string polarising power and even simple compounds like chlorides and bromides have a very large % covalency in nominally ionic bonds.

·      They form complexes, which are often coloured, with a huge variety of ligands. The bonding is dative covalent, but usually called co-ordinate bonding, in transition metal complexes..

·      They are of major importance as industrial catalysts and play a part in biological enzymes

The electron configurations are shown  in Table 1

Table 1
Element
Atomic number
Element Electron
configuration
Common
2+
oxidation states -compounds
other
Scandium
21
1s2 2s22p63s23p63d14s2
18Ar3d1
3+  18Ar
Titanium
22
1s2 2s22p63s23p63d24s2
18Ar3d2
4+    18Ar
Vanadium
23
1s2 2s22p63s23p63d34s2

3+, 4+ and 5+
Chromium
24
1s2 2s22p63s23p63d54s1 *
18Ar3d4
3+ 18Ar3d3; VI 3d0
Managanese
25
1s2 2s22p63s23p63d54s2
18Ar3d5
VII 3d0 - most stable
Iron
26
1s2 2s22p63s23p63d64s2
18Ar3d6
3+ 18Ar3d5- most stable
Cobalt
27
1s2 2s22p63s23p63d74s2


Nickel
28
1s2 2s22p63s23p63d84s2


Copper
29
[Ar]3d104s1 *
18Ar3d9
1+ Ar3d10
Zinc
30
1s2 2s22p63s23p63d104s2
18Ar3d10
none
* Anomalous


Properties of the Elements - Table 2

Element
Metal (ionic ) radii
/ 10-8 cm 
1st ionisation energy
 / kJ mol-1
2nd ionisation energy
 / kJ mol-1
EoM2+ /M
/ V
 density
/g cm -3
melting point
 / oC
Chromium
1.29 (0.73)
653
1592
-0.41
Cr3+/Cr
7.20
1857
Managanese
1.37 (0.67)
715
1509
-1.19
7.20
1242
Iron
1.26 (0.61)
759
1561
-0.44
7.86
1535
Copper
1.28 (0.73)
746
1958
+0.34
8.92
1083
Zinc (3d10)
1.37 (0.75)
906
1733
-0.76
7.14
420
Calcium group II
1.97 (1.00)
590
1145
-2.87
1.54
839



Radii

·      The radii are small for their atomic number. The radii are very similar within the d block This fact is dominant in the physical and chemical properties of the d block.
·      Calcium, in the same period, is 51% larger than the average d block element.
·      There is no uniform decrease in metallic radii across the period.
·      The increasing nuclear charge does make the radii smaller, but the most important factor is the diffuse nature of the d orbitals. When the set of 5 d orbitals  are not full they screen the 4s electrons very poorly from the nuclear charge. The effective nuclear charge is relatively large and radii decrease as the 4s electrons are attracted strongly to the nucleus.
·      Note that Zn, with a full 3d shell, has a relatively large radius, given that it has the largest nuclear charge.
·      The metallic radius is much greater than the ionic radius; since on forming a cation  the  outer shell of electrons is lost.

Ionisation energies I.E. and the formation of positive ions


·      Both 1st and 2nd I.E. are large compared to Group I and II metals. This arises because of the diffuse nature of the d orbitals, poor screening, relatively large effective nuclear charges and small radii. See the discussion of radii above.
To read complete topic click here ................................




Chemistry for class 12 ...........
biodegradable-polymers
electrochemistry
reaction-kinetics
functional-derivatives-of-carboxylic
enzyme-catalysis regulation
carboxylic-acids-and-their-derivatives
introduction-to-d-block-element
transition-metals
coordination-chemistry
solid-state-2
polymer
amino-acidspeptide-and-proteins
benzene-and-aromatic-compounds
solutions-questions
biomolecules



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