Transition Metals

Transition element: it is collectively which has incompletely filled d orbitals in its ground state or in any one of its oxidation states. Electronic configuration of these elements varies from (n-1)d¹ns1-2 to (n-1)d10 ns1-2. Elements of groups 3 to 12 are included in the d-block element. These elements are situated at the middle portion of the periodic table, between the s and p block elements. Since the d-block elements are placed between s and p block elements and are called transition elements.

The d-block elements are further classified into 4 series, depending upon filing of 3d, 4d, 5d, 6d, orbital :-

3d-series: 10 elements are in this series from Sc (Z=21) to Zn (Z=30).

4d-series:10 elements are in this series from Y (Z=39) to Cd (Z=48).

5d-series: 10 elements are in this series from La(Z=57) and from Hf (Z=58) to Hg (Z=80).

6d-series: Ac (Z=89) and from Rf (Z=104) to Uub (Z=112).

Why are d-Block Elements Called Transition Elements?

There are 2 reasons:

They have elements that are ionic (like S blocks) and covalent (like P blocks). Since they require partial attributes, they are placed between s & p  block elements. Elements or elements placed between or intermediate stages that form new blocks are called transitions. Hence they are called transition elements. There are also elements placed between these transition elements, called inner transition elements.

Definition of Transition Element

A transition element is defined as the element which has incompletely filled d orbitals in its ground state or in among any one of its oxidation states. Zn, Cd and Hg aren’t typical transition elements because they need full d10 configuration in their ground state also as in their common oxidation state. However, due to the last members of the three transition series, their chemistry is studied alongside the chemistry of transition metals.

Inner Transition Metals

The f-block elements (numbers 57 to 70 and numbers 89 to 102) are called the innermost transition elements because their position in the periodic table is due to their electron configuration. Atom-filled orbitals basically have lower energy levels than outermost electrons. Therefore, the electron configuration for Nd (Z=60) is [Xe] 6s2 4f4 and the last electron that goes into a 4f orbital is inside the 6s orbital.

General Characteristics of transition elements:

Transition metals form reaction intermediates due to the presence of empty orbitals or their tendency to form different oxidation states. These intermediates provide reaction pathways with lower activation energies, thus increasing reaction rates. These reaction intermediates are easily decomposed to generate products and regenerate original materials. Transition elements form an ample number of coordination complexes. In these complexes, transition metal ions are bound to many anions or neutral molecules. The high tendency of transition metal ions to form complexes is due to 

(i) the small size of atoms and ions. 

(ii) high nuclear charge and 

(iii) availability of empty d orbitals with the correct energy to accept lone electron pairs provided by ligands.

Transition metals make interstitial compounds with elements such as hydrogen, boron, carbon, and nitrogen. Small atoms of these non-metallic elements (H, B, C, N, etc.) are trapped in the interstices of the transition metal atomic lattice. The consequences of filling in the gaps. Transition metals become hard and hard. These interstitial compounds have similar chemical properties to the parent metal, but their physical properties are significantly different, especially density, hardness, and electrical conductivity.

Conclusion

Transition metal collectively which has incompletely filled d orbitals in its ground state or in any one of its oxidation states. General Electronic configuration of d-block : (n – 1)d1-10 ns0-2 , the melting point increases up to the middle then decreases. Hg exists during a liquid state at room temperature. While moving from left to right, Ionisation energy increases but the trend isn’t regular. Successive ionisation enthalpies don’t increase as steeply because of the main group elements with increasing atomic numbers. These elements show variable oxidation states. Usually, these elements and their compounds are coloured because of the presence of unpaired electrons, these are generally paramagnetic. KMnO4 and K2Cr2O7 are good oxidising agents. KMnO4 is prepared from MnO2.