Summary AQA A Level Chemistry - Transition Metals Chemsheets Booklet

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, SECTION 1 – Introduction
1) Electron structure

Remember that:
1s 1s

2s 2p • 4s fills before 3d
3s 3p • 4s also empties before 3d (in ions)
4s 3d • Cr is [Ar] 4s1 3d5
•
Cu is [Ar] 4s1 3d10



• Give the electron structure of the following atoms / ions.


Fe [Ar] ……………………………………… Cu [Ar] ………………………………………

Fe3+ [Ar] ……………………………………… Cu+ [Ar] ………………………………………

Sc [Ar] ……………………………………… Cu2+ [Ar] ………………………………………

Sc3+ [Ar] ……………………………………… Zn [Ar] ………………………………………

V [Ar] ……………………………………… Zn2+ [Ar] ………………………………………

V2+ [Ar] ……………………………………… Cr [Ar] ………………………………………



2) What is a transition metal?


transition metal = element that has an incomplete d sub-shell in either its atoms or one its common ions



metal atom Common ions Transition metal?

Sc Sc [Ar] ………………. Sc3+ [Ar] ……………….

Cu Cu [Ar] ………………. Cu+ [Ar] ………………. Cu2+ [Ar] ……………….

Zn Zn [Ar] ………………. Zn2+ [Ar] ……………….


NB – This is the latest IUPAC definition, but some exam boards incorrectly state that it is an element that has an incomplete
d sub-shell in one of its common ions (and excludes the atoms part) – this only affects scandium in reality but make
sure you are aware if your exam board does this.


3) Properties of transition metals

The incomplete d sub-shell is responsible for a number of general properties of transition elements:

1) variable oxidation states
2) catalytic action
3) coloured compounds
4) formation of complexes


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, SECTION 2 – Complex ions

1) Some definitions

Ligand = particle with lone pair of electrons that bonds to metals by a co-ordinate bond
Complex = metal ion with co-ordinately bonded ligands
Co-ordination number = number of co-ordinate bonds from ligands to metal ion
Lewis base = lone pair donor
Lewis acid = lone pair acceptor



2) Formation of complexes

Common, simple ligands include H2O, NH3 and Cl– ions, all of which have a long pair
of electrons. Complexes are formed when ligands such as these form co-ordinate
bonds using their lone pairs to a metal ion.

In this example, 4 chloride ions (Cl-) act as ligands, each forming a single co-ordinate
bond to the Cu2+ ion using a lone pair, forming the [CuCl4]2- ion.

Ligands are acting as Lewis bases when they bond to transition metals as they
donate a lone pair to form a co-ordinate bond. The metal ion acts as a Lewis acid as
it accepts lone pairs.



3) Shapes of complexes


The table shows the most common shapes of complexes.


linear square planar tetrahedral octahedral

co-ordination
2 4 4 6
number



shape M M M 109.5 M
180 90 90



With larger ligands
(e.g. Cl–) Most complexes
Pt2+ and Ni2+
occurrence Ag+ complexes with small ligands
complexes
(when ligands are (e.g. H2O, NH3)
too big for six to fit)


[Ag(NH3)2]+
example [PtCl4]2- [CuCl4]2- [Cu(H2O)6]2+
(in Tollen’s reagent)




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, 4) Types of ligands

All ligands must have one (or more) lone pair(s) of electrons to form the co-ordinate bond(s) to the metal ion.


Unidentate ligands – ligands which form one co-ordinate bond to a metal ion

Ligand :Cl– :OH– :CN– H2O: :NH3

Example complex [CuCl4]2- [Cr(OH)6]3- [Ag(CN)2]- [Fe(H2O)6]2+ [Cr(NH3)6]3+


Bidentate ligands – ligands which form two co-ordinate bonds to a metal ion


1,2-diaminoethane (en) ethanedioate ion (C2O42-)
Ligand O O
CH2 CH2 C C
- -
H2N: :NH2 O: :O

O
NH2 O C
Example 3+ C O 3-
complex H2N NH2 O O C O
Cr Cr
H2N NH2 O O C O

NH2 C NH
O 2
O C
O
[Cr(NH2CH2CH2NH2)3]3+
[Cr(C2O4)3]3-


Multidentate ligands – ligands which form more than two co-ordinate bonds to a metal ion


EDTA4- forms 6 bonds porphyrin forms 4 bonds
Ligand

-
:OOC CH2 CH2 COO:-

:N CH2 CH2 N:
-
:OOC CH2 CH2 COO:-




How it globin
bonds
N:
N: Fe2+ :N
:N
O2 or H2O


Example [Cu(EDTA)]2- haemoglobin


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