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A2 Transition Elements 1




The Transition Elements (dblock)

The transition elements are the elements in the middle of the periodic table. There are three rows of transition metal
we shall only be concerned with the first row.

The definition of a transition metal that we shall use is:
An element…

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A2 Transition Elements 2




26 Fe2+


26 Fe3+


27 Co2+


25Mn4+

The transition elements form a series of fairly closely related elements. The variation of atomic size
and first ionisation energy across the series is fairly small and they show a set of characteristic
properties.



Characteristics of Transition Metals:



They…

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A2 Transition Elements 3





A complex ion consists of a central transition metal ion surrounded by LIGANDS.


LIGANDS may be negative ions or neutral molecules. The ligands bond to the transition
metal ion by using lone pairs to form dative covalent bonds, i.e. by donation of electrons
into vacant d,…

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A2 Transition Elements 4









Transition metal complexes do NOT obey VSEPR rules so that, although 6 coordinate complexes are virtually
ALWAYS OCTAHEDRAL, 4 coordinate complexes may be tetrahedral or square planar.
Differences may be subtle, e.g. [CuCl4] is planar in (NH4)2[CuCl4] but tetrahedral (approximately) in Cs2[CuCl4].

Oxidation state of central…

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A2 Transition Elements 5





The [Fe(H2O)6]3+ can then only be prepared in strongly acidic solution (Le Chatelier)









Polarisation of water by Fe3+




If a high concentration of cyanide (!) ions is added to a solution containing the [Fe(H2O)6]3+ ion, the [Fe(CN)6]3 ion
can be formed:

[Fe(H2O)6]3+(aq) + 6CN [Fe(CN)6]3(aq) +…

Page 6

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A2 Transition Elements 6




2 2 2

1 1 1 1 1 1 1

0 0 0 0 0 0 0 0
1 1 1 1 1 1 1


2 2 2 2 2 2 2 2


3 3 3 3 3 3 3 3

4 4 4 4 4…

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A2 Transition Elements 7










IRON(III)
The most common oxidation states for iron are +2 and +3.

Oxidation state +3

Most iron(II) salts are oxidised slowly by the air to iron(III) salts.

The pale violet hexaaquo ion is found in the solid state but cannot exist in neutral aqueous solutions because…

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A2 Transition Elements 8




[Cr(H2O)6]3+ + H2O [Cr(H2O)5(OH)]2+ + H3O+

The addition of alkali to Cr3+(aq) results in formation of Cr(OH)3, which dissolves in excess alkali to form a complex
which may be [Cr(OH)6]3. Chromium (III) hydroxide is thus showing amphoteric properties, i.e. the tendency to
react with both acids…

Page 9

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A2 Transition Elements 9





2Cu2+(aq) + 4I(aq) 2CuI(s) + I2(aq)
white
precipitate












Formation of Coloured Complexes ­ Ligand Field theory

[Cu(H2O)6]2+ blue

[Cu(NH3)4(H2O)2]2+ deep blue/violet

[Fe(SCN)(H2O)5]2+ blood red

[Ni(H2O)6]2+ green


Formation of coloured complex ions/compounds requires the presence
of a partiallyfilled d subshell.


Energy in the form of visible light…

Page 10

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A2 Transition Elements 10




dd transitions electronic transitions between d orbitals





Cu+ complexes/compounds are usually colourless because copper(I) has a full d subshell. For the same reason
zinc(II) compounds are colourless. Sc3+ has no d electrons and is colourless.









Catalytic Ability

The elements and their compounds/complexes can act as catalysts.…

Comments

Uman Nulla

Quite long notes for just one topic

Hajra

Just what I needed! Thank you X

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