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Technetium, the lightest radioactive element! Technetium, the lightest radioactive element! Among all transition elements technetium (Tc, Z=43, A=98 for most stable isotope) is the only element that does not exists in nature. It is the lowest atomic number element without any stable isotopes; every form of it is radioactive. Its unstability is explained by Mattauch's rule which states that if two elements with consecutive atomic numbers each have an isotope of the same weight, one of the isotopes will be unstable and radioactive. Elements Mo (Z=42) and Ru (Z=44), which are adjacent to Tc in periodic table have stable isotopes with mass number 98. So, Tc has only unstable radioactive isotopes. And also atomic nuclei with an odd number of protons are less stable than those with even numbers, even when the total number of nucleons (protons + neutrons) is even. This is due to unsymmetrical arrangement of nucleons in the nucleus.

Learning Objectives

After completing the topic, the student will be able to:

  • List the d‐block elements and identify their position in periodic table.
  • Write the electronic configuration of d‐block elements and give the reasons for anomalous electronic configuration of some elements.
  • Define transition metals and recognize the difference in transition metals and d‐block elements.
  • Discuss the general physical and chemical properties of d‐block elements.
  • Appreciate the relative stability of oxidation states of transition metals.
  • Calculate the spin only magnetic moments of transition elements.
  • Discuss in detail about preparation methods, properties and uses of potassium dichromate (K2Cr2O7) and potassium permanganate (KMnO4).
  • Describe the methods of extraction of iron and copper.
Peculiar elements of d-block Peculiar elements of d-block Ruthenium is a rare transition metal belonging to the platinum group of the periodic table. Mercury is a liquid metal. Osmium is a hard, brittle, blush-white transition metal in the platinum family and is the densest naturally occurring element.
Periodic table
 Periodic table The transition elements are those elements having a partially filled d or f subshell in any common oxidation state. The term “transition elements” most commonly refers to the d–block transition elements.

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d-block elements

The discovery of elements started about 800 years ago, when people obtained shining materials from the rocks by heating. Iron, copper, silver and gold are the transition elements which played a very important role in the development of human civilization. Some inner‐transition elements (Th, Pa, and U) are the source of nuclear energy.

The elements in which the differentiating electrons enter into d‐subshell or called d‐block elements.

All d‐block elements exhibit (n−1) d1‐10 ns1‐2 electronic configuration. Some characteristic features of the electronic configurations of the transition elements are: Atoms of all transition elements consist of an inner core of electrons having noble gas configuration. For example, Sc : [Ar]3d14s2, Y : [Kr]4d15s2, La : [Xe]5d16s2. The half‐filled and completely filled d‐orbitals gain extra‐stability. So, such configurations are favored wherever possible.

Why the name 'transition elements'?

The properties of these elements are in between s‐block and p‐block elements i.e., d‐block elements represent change or transition in properties from most electropositive s‐block elements to least electropositive p‐block elements. Therefore these are called as transition elements.

Position of transition elements inthe periodic table:
The d–block elements are located between Group 2 and Group 13 starting from the fourth period in the form of four series of elements, as shown in the periodic table. Thus, the elements of Groups 3 to 12 belonging to the periods 4 to 7 are d–block elements.

The transition elements include, Coinage metals (such as, silver, gold and platinum and industrially important metals (such as iron, copper, vanadium, titanium, manganese, palladium etc).

Coinage metals

The three non-radioactive elements of group 11 of the periodic table: copper, silver and gold are usually known as coinage metals. These are longest-known and most familiar elements that are known for their soft, shiny and conducting properties. Because of their softness, these metals are easily molded as coins. Besides attractiveness, rare occurrence in Earth's crust made them a symbol of “wealth”. They are also easily identified by characteristic color [copper (reddish), silver (white) and gold (yellow)] and are often found in uncombined state. Among these elements, copper is mostly used in making electrical components and alloys (brass , bronze, etc). Gold and silver, due to their attractiveness and better resistance to oxidation, are used in jewelry and ornamental works. A small amount of gold can be pounded into a foil of extreme thinness. These metallic elements are considered as a precious part of transition elements since their di positive ions have partially filled d–subshells.

Zinc metals

The elements of Group 12 (zinc, cadmiun, mercury) posses completely filled d–subshells either in the ground or ionic state. Due to possessing a completely filled electronic configuration, these metals differ in certain properties like having low melting point, poorly forming metallic bond, etc. Zinc and cadmium are soft metals that easily oxidize to get +2 oxidation state. Mercury is a shiny liquid metal (at room temperature) that oxidizes with great difficulty.Zinc is used in making alloys and as galvanizing agent. Cadmium available as cadmium yellow (cadmium sulfide) and cadmium red (cadmium selenide) is used in paint manufacture.Mercury conducts electricity and has been used in thermometers for long time