The Transition Metals

The Transition Metals are the elements found between the Group IIA Elements and the Group IIB Elements in the periodic table. The GroupIIb are sometimes considered transition elements. The transition elements are also known as the d-block elements, because while the outermost level contains at most two electrons, their next to outermost main levels have incompletely filled d sub-orbitals, which are filled-up progressively on going across the periodic table from 8to 18 electrons. The filling of the d sub-orbitals of the transition elements across a row of the periodic table is not always regular.


Electron configuration of the Transition Metals

The electronic configuration of these elements are characterised as having full outer orbitals and as having the second outermost orbitals incompletely filled. Thus, in the case of the first transition metals series, the electronic configuration of the outer orbitals is 4s2, while the second outermost orbitals (i.e. the 3d level) are incompletely filled.

Because they are elements whose atoms have their next-to-outer most main levels incomplete at the inner d sub-levels, but are filling up progressively, while the outer most level contains at most two electrons, the filling of the d orbitals is not always regular.

There are four transition series :

  1. The first transition series : Scandium (Sc) through Copper (Cu): 3d subshell is filling.

    Irregularities are observed for Chromium, Cr, and Copper, Cu, because the listed electronic configurations are energetically favoured (i.e. 3d54s1 is more stable than 3d44s2, and 3d104s1 is more stable than 3d94s1 respectively.).

  2. The second transition series : Yttrium (Y) through Silver (Ag): 4d subshell is filling.

    Irregularities are observed for Nb which skips from 4d25s2 to 4d45s1, and Pd, which goes from 4d85s2 to 4d105s1.

  3. The third transition series : Lanthanum (La) to Hafnium (Hf) through Gold (Au)): 5d subshell is filling.

    Irregularities are observed for Pt which skips from 5d96s2 to 5d106s1.

  4. The forth transition series which is incomplete : Actinium (Ac) to element 104 through element 109: 6d subshell is filling , If elements 110 and 111 are found then this will complete this series..


Properties of Transition Metals

The Properties of Transition Metals are largely dependent on the electronic configuration of the electrons in the outer shell and in the penultimate outer shell.

The transition elements readily form alloys with themselves and with other elements (e.g. a copper-tin alloy is used for mirrors, brass is a copper-zinc alloy). Tungsten, is used to make tools and filaments in light bulbs.

The atomic size is fairly constant since the electrons in the outer most shells have similar environments.

The low ionisation potentials mean that the elements show variable valency states by loss of electrons from the s and 3d orbitals.

The elements in this group can have different oxidation states which makes them useful as catalysts.

Compounds of the transition elements can be paramagnetic (i.e. attracted by a magnetic field) or diamagnetic (i.e. not attracted by a magnetic field). Paramagnetism in the transition elements is caused by the presence of unpaired electrons in the d sub-orbital. Diamagnetism is characteristic of compounds where all the electrons are paired in the d sub-orbitals.


Physical Properties of Transition Metals

Apart from Copper, the transition metals are all white lustrous metals. They vary widely in abundance (e.g. Iron, Fe, and Titanium, Ti, are plentiful, Scandium, Sc, is rare). They have high melting points and high densities. This suggests that the electrons which enter the d orbitals are being used to bind the atoms together in the crystal lattice.

The transition elements form Complex Ions.

Examples of these compound ions include

(a) Ferrocyanide Ion, Fe(CN)6(4 -) in Potassium Ferrocyanide, K4Fe(CN)6, and,

(b) Chromate Ion, CrO4(2 -), in Barium Chromate, BaCrO4.

Most compounds of the transition metal are coloured. There are variations in colour for compounds of the same valency, and with different valency (oxidation) states. For example,

A Coordination Complex is a compound in which molecules or ions form coordinate bonds to a central metal atom or ion. The complex may contain positive ions, negative ions or neutral molecules. The formation of such coordination complexes is typical behaviour of transition metals.

Diamagnetism is magnetic characteristic of those transition metals where all the electrons in the d sub-orbitals of the atoms are paired, and results in these elements not attracted by a magnetic field.

The Sub-Group Ib Elements are the transition metals Copper, Silver and Gold.

The Group III Elements in the periodic table are divided into two Sub-Groups.

The Sub-Group IIIa Elements, which are also called the main group elements, are Boron, Aluminium, Gallium, Indium and Thallium. The main group is essentially a group of weak metals, which have two s-electrons and one p-electron in their valence shells. Unlike the elements found in Groups I and in Group II, the Group III elements have more than one oxidation state, being the first members of the p block.

The Sub-Group IIIb Elements are the transition metals Scandium, Yttrium, Lanthanum, which is generally classified with the Lanthanoids and Actinium, which is generally classified with the Actinoids.

The Group IV Elements in the periodic table are divided into two Sub-Groups.

The Sub-Group IVa Elements, which are also called the main group elements, are Carbon, Silicon, Germanium, Tin, and Lead. These elements have two s electrons and two p electrons in their valence shells. The p electrons give rise to a +2 oxidation state while the s and p electrons give rise to a +4 oxidation state. The +4 oxidation state is formed due to an s electron being promoted to a vacant p orbital when the atom attains an excited state.

The Sub-Group IVb Elements consists of the three elements Titanium, Zirconium, and Hafnium. These three elements are generally classified with the transition elements.

The Group V Elements in the periodic table are divided into two Sub-Groups.

The Sub-Group Va Elements, which are also called the main group elements, are Nitrogen, Phosphorus, Arsenic, Antimony, and Bismuth. There are five electrons in the valence shells of these elements (i.e. two s orbital electrons and three p orbital). Thus, the principal oxidation state of these elements are +3 and +5 for the main group elements.

The Sub-Group Vb Elements are Vanadium, Niobium, and Tantalum. These three elements are generally classified with the transition elements.

The Group VI Elements in the periodic table are divided into two Sub-Groups.

The Sub-Group VIa Elements, which are also called the main group elements, are Oxygen, Sulphur, Selenium, Tellurium, and Polonium. These elements have two electrons short of the electronic configuration of a Nobel Gas. Thus, the oxidation states +2, +4, and +6 are found in the elements of this group.

The Sub-Group VIb Elements are Chromium, Molybdenum and Tungsten. These three elements are generally classified with the transition elements.

The Group VII Elements in the periodic table are divided into two Sub-Groups.

The Sub-Group VIIa Elements, which are also known as the Halogens (i.e. the main group elements), are Fluorine, Chlorine, Bromine, Iodine and Astatine. These elements are non-metals and are too reactive to occur on their own in nature. Thus, they are usually found combined with other elements in a salt.

The Sub-Group VIIb Elements are the metallic transition elements Manganese, Technetium, and Rhenium. These three elements are generally classified with the transition elements.

The Group VIII Elements in the periodic table are a group of nine transition elements consisting of the platinum metals. This group consists of three triads of elements Iron, Ruthenium, Osmium, Cobalt, Rhodium, Iridium, and Nickel, Palladium Platinum. These elements are generally classified with the transition elements.

Inner Transition Metals

The Inner Transition Metals are the series of elements

(a) from Cerium (Atomic Number 58) to Lutetium (Atomic Number 71), which are called the Lanthanoids, and

(b) from Thorium (Atomic Number 90) to Lawrencium (Atomic Number 103), which are called the Actinoids.

The inner transition elements are found between Group 2 and the transition elements in the fifth row of the periodic table. The transition elements are also known as the f-block elements.

These two series make up the f-block elements in the periodic table, and their chemical properties of the elements derive from the filling of the f atomic sub-orbitals. The electronic configuration of these elements are characterised as having full outer orbitals and full second outermost orbitals, while the second outermost orbitals are incompletely filled. Thus, in the case of the first inner transition metals series, the electronic configuration of the outermost and second outermost orbitals is 4s2 3d10, while the third outermost orbitals (i.e. the 4f level) are incompletely filled.

The Main Group Elements in the periodic table can be classified as either being metals or non-metals. The vertical columns in the table are called groups. Elements within the same group all have the same number of electrons in their outer shell. Group 1 are known as Alkali metals. Group II are known as the Alkaline earth metals and the group of elements between group II and III are known as the transition metals.

Paramagnetism in the transition elements is caused by the presence of unpaired electrons in the d sub-orbital, and results in these elements being attracted by a magnetic field.



Compound			Formula		        Colour

Anhydrous Copper Sulphate	Cu(II)SO4,		White

Hydrated Copper Sulphate	Cu(II)SO4.5H2O 	        Light 
							Blue
Ammoniacal Copper Sulphate     [Cu(II)(NH3)4]SO4	Dark 
							Blue
Potassium Permanganate	        KMnO4	               	Purple

Potassium Dichromate		KCrO4		        Orange

Potassium Chromate		K2Cr2O4		        Green

V(+++++) is pale yellow, 
V(++++) is blue, 

The colour exhibited by the transition metal ions is due to their ability to absorb light in the visible region of the electromagnetic spectrum. This causes unpaired d electrons to rise from a lower to a higher energy state. Ions which have the electronic configuration 3d(10), including the Scandium (III) Ion, Sc(+++) and the Copper (I) Ion, Cu(+), are colourless, because they have no unpaired d electrons.

Compounds of the transition elements can be paramagnetic (i.e. be attracted by a magnetic field) or diamagnetic (i.e. not be attracted by a magnetic field). Paramagnetism in the transition elements is caused by the presence of unpaired electrons in the d orbitals. Diamagnetism is characteristic of compounds where all the electrons are paired in the d orbitals.

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