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Summary Notes 3.2.5 - Transition metals and the Reactions of Aqueous Ions(A-level only)
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Summary Notes 3.2.5 - Transition metals (A-level only)
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Taylor’s Notes Transition Metals and Reactions of Aqueous Ions NotesTransition Metals and d-Block Elements
The term ‘d-block elements’ refers to those elements in which this d-subshell is filing (Sc-Zn),
A transition element is an element with one or more stable ions with a partially filled d subshell
Zinc is not included as a transition metal because its only common oxidation state is Zn2+ configuration: 1s22s22p63s23p63d10
Scandium is not included as a transition metal because its only common oxidation state is Sc3+ configuration: [Ar] but Scandium configuration:
[Ar]4s23d1
The distinction of scandium and zinc is made because the main features of the chemistry of the transition elements depend largely on this
partially filled d-subshell
Electronic Configurations of the d-block Elements and their Simple Ions
The stability of the half-filled subshell means that d5 and d10 configurations are particularly stable:
Cr - 1s22s22p63s23p64s13d5
Cu - 1s22s22p63s23p64s13d10
Notice that the 4s is half filled due to the extra stability mentioned above
In ions, the 4s electrons are always lost before the 3d electrons:
Fe2+ - 1s22s22p63s23p63d6
Fe3+ - 1s22s22p63s23p63d5
Fe3+ is more stable than Fe2+ because the electronic configuration of Fe3+ is [Ar]3d5 and Fe2+ is [Ar]3d6, therefore Fe3+ is more stable because of
the partially filled d-subshell
General Properties of Transition Metals
Transition metals have higher melting points, higher boiling points and higher densities than other metals, but transition metals do also show
the following characteristic properties:
• Variable Oxidation States – transition metals have electrons of similar energy in both the 3d and 4s levels and the elements can form
ions of roughly the same stability by losing different numbers of d-subshell electrons
• They can form Complex Ions – transition metals that have empty spaces in their 3d-orbitals, can receive lone pairs of electrons and
form dative covalent bonds and thus produce complex compounds
• They form Colour Compounds – when electrons move from a d-orbital (with lower energy) to another d-orbital (with higher energy),
energy is taken in, this energy is in the form of visible light – the transition metal appears the complementary colour to the light
absorbed, thus producing coloured compounds
• They have Catalytic properties – as T-M have variable oxidation states, they tend to have catalytic properties
Redox Chemistry of Vanadium
Vanadium can form four oxidation states, each with a different colour
Oxidation Number 5 4 3 2
Species Present VO2+ VO2+ V3+ V2+
Remember the colours as ‘you’d better get vanadium’ – VO2+ (yellow), VO2+ (blue), V3+ (green) and V2+ (violet)
Electrode Half Equation E/V
Zn2+ + 2e- ⇌ Zn - 0.76
V3+ + e- ⇌ V2+ - 0.26
Cu2+ + 2e- ⇌ Cu + 0.34
VO2+ + 2H+ + e- ⇌ V3+ + H2O + 0.36
I2 + 2e- ⇌ 2I- + 0.54
Fe3+ + e- ⇌ Fe2+ + 0.77
VO2+ + 2H+ + e- ⇌ VO2+ + H2O + 1.00
Br2 + 2e- ⇌ 2Br- + 1.07
MnO4- + 8H+ + 5e- ⇌ Mn2+ + 4H2O + 1.51
Which reagents can change VO2+ to VO2+ - I- or Fe2+ because their E value is more negative than the E value of VO2+
Which reagents can change VO2+ to V2+ - Zn because Zn’s E value is more negative than the E value VO2+ to VO2+ and VO2+ to V3+ and V3+ to V2+
, Taylor’s Notes Transition Metals and Reactions of Aqueous Ions Notes
Complex Ions
Water molecules, hydroxide ions, ammonia molecules and cyanide ions can all link to a transition metal to form complex ions, they do so by
donating a lone pair of electrons to form a bond, this is a dative covalent bond – the ions or molecules that form these bonds are called ligands
A complex ion is one in which a central positive ion is surrounded by ligands which are co-ordinately (datively) bonded to it
A ligand is a molecule or negative ion which has a lone pair of electrons and can use its lone pair of electrons to form co-ordinate bonds to a
metal ion
The coordination number is the number of co-ordinate/dative covalent bonds
A Lewis base is an electron pair donor whereas a Lewis acid is an electron pair acceptor
Transition metals are not unique in forming complexes, but they form a much wider range than other elements, this is because the transition
metals are small and polarising, since they attract ligands strongly
Naming Complex Ions
1st Part 2nd Part 3rd Part 4th Part
Number of each type of ligand Name of Ligand Name of Transition metal (ending in Charge on transition metal
-ate if it is a negative ion)
Ligand Name Ligand Name
H2O Aqua NH3 Ammine
Cl- Chloro OH- Hydroxo
CN- Cyano F- Fluoro
When writing formulae, the central ion is put first, then the negative ions and then follow any neutral molecules – everything is then put in
square brackets and the charge added:
[Pt(NH3)4]2+ = tetraammineplatinum (II) [Cr(H2O)6]3+ = hexaaquachromium (III) [Ag(NH3)2]+ = diamminesilver (I)
[Cu(NH3)4(H2O)2]2+ = tetraamminediaquacopper (II) [CrCl4]- = tetrachlorochromate (III) [Al(OH)4(H2O)2]- = tetrahydroxodiaquaaluminate (III)
Changes in Oxidation State in Transition Metals
The ease with which a transition metals can change oxidation state depends on the pH and the ligands present
In general, it is easier to: oxidise a transition metal in alkaline conditions and reduce a transition metal in acidic conditions
Types of Ligand
Monodentate ligands are ligands which form one co-ordinate/dative covalent bond to a metal ion such as H2O, Cl-, CN-, OH- and NH3
Bidentate ligands are ligands which form two co-ordinate/dative covalent bonds to a metal ion such as en (1,2-diaminoethane) and C2O42-
(ethanedioate ion)
1,2-diaminoethane (en) Ethanedioate ion (C2O42-)
Ligand
[Cr(en)3]3+
[Cr(C2O4)3]3-
[Cr(NH2CH2CH2NH2)3]3+
Example
Complex
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