Chapter 2:- Transition Elements

B.sc 2nd year Book
(Page 1)

# Transition Elements

## What are transition Elements?

The elements located in groups 3-12 of the modern Periodic Table are called transition elements. These elements have partly filled d – sub-shell in their elementary form and are called d – Block elements. However, since Zn, Cd and Hg which completely fill the d orbital, are not regarded as transition elements due to their electronic configurations which correspond to the electronic configuration of (n-1)d10 ns2.
Approximately, 75 percent of the elements known are metals, and among these most important are transition metals. The industrial revolution began only after the development of extraction methods of transition metals.

These elements lying between s- and p-block elements of the periodic table, d-block elements are also termed as transition or ‘transitional elements’ (T. E’s.) because of the following reasons –

(i) We know s- block elements are more electropositive and have a strong tendency to transfer one or more electrons of their outermost shell whereas p – block elements are known to be more electronegative and have a strong tendency to gain electrons so as to attain a stable electronic configuration. On the other hand, d-block elements form various compounds in which they have properties either similar to s-block or p-block or of both the s- and p-block elements, For example, in the formation of FeCl3, iron transfers its three valence electrons to three chlorine atoms to carry +3 charge, in metal carbonyls such as Fe(CO)5, iron gains ten electrons from five carbonyl groups to attain an effective atomic number equal to the nearest noble gas i.e. Kr, but in the formation of complex ions of the type [Fe(CN)6)]4- ion, iron first loses two electrons and then to gain twelve electrons from six cyanide ions to attain stable nearest noble gas configuration. In these three different compounds FeCl3, Fe(CO)5 and [Fe(CN)6]4- ion, the central atom shows both the properties of s-block, p-block, s-block, and p-block, respectively. Thus, the Fe atom may have its position in the periodic table between s-and p-block and is considered a transitional element.

(ii) d- block members have a unique tendency to form complexes in which the central metals generally have incomplete (n-1)d-subshell. These complex compounds absorb visible light due to which d-d electronic transition may occur which is responsible for color of the complexes. Hence the term ‘transition‘ is used before the metal.

Classification of Transition Elements

We have therefore defined the transition elements as the series of 10 metals from scandium to zinc, yttrium cadmium, and lanthanum to mercury (omitting cerium to luteniam). Thus, d-block elements are classified into four series each containing ten elements.

1. First transition series or 3d-series: From Seandium (Z=21) to zinc (Z=30).
2. Second transition series or 4d-series: From Yttrium (Z=39) to cadmium (Z=48).
3. Third transition series or 5d – series: From Lanthanum( Z = 57), Hofnium (Z=72) to mercury (Z=80).
4. Fourth transition series or 6d- series: From Actinium(Z=89), Rutherfordium (Z=104) to Ununbium (Z=112) corresponding to the filling of 3 d-, 4 d-,5 d- and 6 d-orbitals of (n-1)th main shell.

In these elements the differentiating electron enters (n-1)d-orbitals of (n-1)th main shell. Thus, the outermost main shell of these elements is incomplete.

## What are the Properties of Transition Metals

The following are the properties of transition elements:

• Ductile: They are highly ductile i.e. they can be stretched into a very thin wire.
• Malleable: They are highly malleable which means It is the ability of a solid to bend or be hammered into other shapes without breaking.
• High electrical conductivity: They have the ability to conduct a large amount of electrical current.
• High thermal conductivity: They are able to effectively transfer heat and readily take up heat from their environment.
• High enthalpies of atomization: Due to having a highly effective nuclear charge and a large number of valence electrons, they form very strong metallic bonds which results in high enthalpies of atomisation.
• High density: They are usually robust and hard, with high densities.
• High melting and boiling point: They have high melting and boiling point.
• Oxidation states: Because transition metals have vacant (n-1)d orbitals that are closer to the outermost ns orbital in energy levels, they exhibit varying oxidation states. These orbitals never fill completely. Hence, (n-1)d orbitals can always accommodate additional electrons.
• Density: The density of d-block elements is high because of their small atomic size and high metallic bonding.
• Catalytic properties: Due to the presence of unpaired electrons that can form complexes, the transition elements have catalytic characteristics. The most vital catalysts are iron and vanadium. For eg., Ammonia is produced with the aid of iron, which serves as a catalyst.

## What are the General Characteristics of Transition Metals

Compounds with a variety of transition elements are distinguished by their capacity for having a wide range of vibrant colours. The d-orbitals of a transition metal complex immersed in water absorb light of different energy as it passes through. An unabsorbed form of visible light at a certain energy level results in a transparent coloured solution.

Transitional metals have a shiny, metallic appearance. Gold and copper have colours that are not present in any other element on the periodic table, unlike the majority of transition metals (such as iron or silver, which are often greyish or white).
Many paramagnetic compounds are formed by these elements, because of the unpaired electrons in the d orbital.

1. What are transition metals?

Transition elements, also called transition metals, are defined by the International Union of Pure and Applied Chemistry (IUPAC) as elements that have partially filled d orbitals or the ability to form stable cations with an incompletely filled d orbital. In simpler terms, transition elements are those that have electrons in their d subshell that are not completely filled or have the ability to form positive ions with partially filled d orbitals.

2. What is unique about transition elements?

Transition metals exhibit high melting points and densities compared to other metals, and they are known to possess catalytic properties.

3. Uses of Transition Metal in Daily Life?

Iron used as a catalyst in the production of ammonia through Haber’s process. Cobalt is utilized in the production of paints and pigments due to its vivid blue color, and it is commonly employed in rechargeable batteries. Copper is regarded as the most efficient conductor of electricity and is utilized in electronics as wires.

4. Which is the most abundant transition?

Iron (Fe) is the most abundant transition metal on earth and has significant roles in natural processes. It was among the first transition metals successfully employed in chemical synthesis.
5. Does transition elements react with water?
The majority of transition elements have little or no reaction with cold water, whereas iron reacts with water and oxygen at ambient temperature to create hydrated iron(III) oxide, commonly known as rust.