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.
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.
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, (such as, silver, gold and platinum and (such as iron, copper, vanadium, titanium, manganese, palladium etc).