Properties of transition elements (A-level inorganic chemistry)
Transition elements, general properties
Definition
Transition elements are elements with partially filled d-orbital
Members
| Elements | Atomic number | Electronic configuration |
| Sc Ti V Cr Mn Fe Co Ni Cu Zn |
21 22 23 24 25 26 27 28 29 30 |
[Ar] 3d1 4s2 [Ar] 3d2 4s2 [Ar] 3d3 4s2 [Ar] 3d5 4s1 [Ar] 3d5 4s2 [Ar] 3d6 4s2 [Ar] 3d74s2 [Ar] 3d8 4s2 [Ar] 3d10 4s1 [Ar] 3d10 4s2 |
Properties of transition metals
(a) Physical properties
They are hard metals, with high melting and boiling points due to strong interatomic bonding that involves the participation of both the 4s- and 3d-electrons.
They are good conductors of heat and electricity due a big number of delocalized electrons in s- and d- orbitals.
They have high densities are due to small atomic radii and high atomic masses.
(b) Paramagnetism
Due to presence of unpaired electrons transition metals are weakly attracted by a magnet but they lose their magnetism in the absence of magnetic field.
Those that are strongly attracted by a magnet are said to be ferromagnetic, e.g., iron, cobalt and nickel.
(c) Formation of colored ions
Most compounds and complexes of transition metal ions are colored, with the actual color depending on the oxidation states of the central ions.
For example
Fe2+ is green
Fe3+ is brown
Reason for formation of colored ions
Transition metals form colored ions because electron transitions in their ions or complexes produce or absorb radiations within the visible part of the spectrum.
(d) Complex ions formation
Transition metals form many complex ions; e.g. [Fe(CN)6]3-
Definitions
A complex ion is the one that contains a central ion linked to other atoms, ions or molecules called ligands through dative bonds.
A dative bond is a covalent bond in which the shared electron pair is contributed by a single atom.
Why transition element form complexes
- The ions of transition elements have a high charge density to attract electrons.
- The ions of transition elements have vacant d-orbitals that can accommodate electron pairs to form dative bonds
A coordination number is the number of ligands that form dative bonds with the central ions. For example; [Fe(CN)6]3- has a coordination number 6
Trial 1
Determine the oxidation states and co-ordination numbers of the central metal ions in each of the following complexes.
| Complex | Oxidation state | Coordination number |
| Cu(NH3)4(OH)2 | ||
| [Cr(H2O)5Cl]Cl2.H2O | ||
| [Co(CN)]3- | ||
| Cr2O72- |
Trial 2
One of the properties of transition metals is complex ion formation
(a)(i) Define the term ‘complex ion’. (2 marks)
(ii) Explain why transition metals form complexes (2 marks)
(b) Fe(CN)63- and [CuCl4]2- are complexes formed by iron and copper respectively.
State;
(i) The oxidation states of;
Iron
Copper
(ii) The co-ordination numbers of;
Iron
Copper (2marks)
(e) Variable oxidation states
Most transition metals exhibit variable positive oxidation states. For example, iron has Fe2+ and Fe3+.
Transition metals form variable oxidation state because they have many electrons in the outermost shell with almost the same energy
(f) Catalytic activity
Transition metals have high catalytic activity. The transition metals use their variable oxidation states to provide alternative mechanisms to the reactions that require low activation energies thus speeding up chemical reactions.
Definition
A catalyst is a substance that speeds up a chemical reaction without taking part in the reaction.
Example:
V2O5, in Contact process
(g) The formation of interstitial compounds
The sizes of transition metal atoms and their crystal structures are such that small atoms like hydrogen, boron, carbon and nitrogen can occupy the spaces within the crystal and form interstitial compounds. No definite chemical formula can be attached to these substances since they are nonstoichiometric.
Trial 3
With reference to transition metals, explain what is meant by the following:
(a) Complex-ion, (5 marks)
(b) Catalytic activity, (3 marks)
(b) Colored ion formation. (5 marks)
Scandium
It is the first element in the first transition series. Apart from having partially filled d-orbital; it shows no other property of transition elements. It has a fixed oxidation state of +3.
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