Transition Metals Notes 5.2.4 aqa

Transition Metal Notes

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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 which forms at least one stable ion with a partiallyfilled d subshell
Sc and Zn are NOT transition elements
According to this definition scandium and zinc must be omitted from the list because the only ion formed by
scandium is the 3+ ion and that formed by zinc is the 2+ ion. Sc3+ has no d electrons, Zn2+ has d10, i.e. a full d
Electronic configurations of transition metals:
The 4s orbital is filled before the 3d
since it is lower in energy. The electronic configurations are thus of the form
[Ar] 3dn 4s2
26 Fe :
Chromium and copper are exceptions to the general rule and both have one electron in the 4s orbital,
You do not need to know that the electronic configurations of Cr and Cu are different.
e.g. Cr : [Ar] 3d5 4s1
29 Cu :
Ionisation of transition elements
The 4s electrons are always removed before the
3d electrons
Thus the electronic configurations of some transition metal ions are:
Electronic configuration

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A2 Transition Elements 2
26 Fe2+
26 Fe3+
27 Co2+
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
Characteristics of Transition Metals:
They are all typical metals, i.e. they have
high melting points and densities.
They form complex ions.
They can exhibit more than one oxidation
state in compounds/complexes.
They usually form coloured
compounds/complexes.…read more

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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, s or p orbitals on the central ion. Forming a coordinate bond
e.g.…read more

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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 atom Geometry
[Fe(CN)6]3 Octahedral
[Cu(NH3)4]2+ (Square Planar)*
[Ag(NH3)2]+ Linear
[CuCl4]2 Tetrahedral
* actually [Cu(NH3)4(H2O)2]2+, a distorted octahedral complex.…read more

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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) + 6H2O
If ammonia solution is added to a solution of silver nitrate the colourless [Ag(NH3)2]+ ion is formed:
[Ag(H2O)2]+ + 2NH3(aq) [Ag(NH3)2]+(aq) + 2H2O(l)
This is also formed in an extension of the test for…read more

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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 4 4 4
5 5 5 5
6 6 6
The greatest number of oxidation states and the highest oxidation states are found in the middle of the series.…read more

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A2 Transition Elements 7
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.…read more

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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 (a salt would be formed with acids) and bases.
The 3+ oxidation state is the most stable and common one for chromium.…read more

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A2 Transition Elements 9
2Cu2+(aq) + 4I(aq) 2CuI(s) + I2(aq)
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 can be absorbed to cause rearrangement of electrons within the d subshell.
In the presence of 6 coordinate complexes (octahedral) the 3d orbitals in a transition metal ion are no longer
degenerate.…read more

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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.
e.g.…read more


Uman Nulla

Quite long notes for just one topic


Just what I needed! Thank you X

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