Write about variable oxidation state and magnetic properties of d-block elements
Answers
Transition Elements
Transition elements are those elements that have partially or incompletely filled d orbital in their ground state or the most stable oxidation state. The partially filled subshells of d-block elements incorporate (n-1) d subshell. All the d-block elements carry a similar number of electrons in their furthest shell. Hence, they possess similar chemical properties.
Placement of Transition Elements in the Periodic table
transition elements
(Source: Wikimedia)
The transition elements are placed between S and P block elements. They are divided as first transition series (the elements from Sc to Cu), the second transition series (the elements from Y to Ag), and the third transition series (the element La and the elements from Hf to Au).
Actinium (Ac) is the first member of the fourth transition element series, which also consists elements from Rf to Rg. II- B Zn, Cd, and Hg and III- A Sc, Y, La, and Ac are non-typical transition elements while the remaining are typical transition elements.
General Properties
All transition elements exhibit similar properties because of the identical electronic configuration of their peripheral shell. This happens as each additional electron enters the penultimate 3d shell. This creates an effective shield between the nucleus and the outer 4s shell. The peripheral shell configuration of these elements is ns2. The general properties of the transition elements are as follows:
form stable complexes
Have high melting and boiling points
Contain large charge/radius ratio
Form compounds which are often paramagnetic
Are hard and possess high densities
Form compounds with profound catalytic activity
Show variable oxidation states
form coloured ions and compounds.
Metallic Nature
As there is less number of electrons in the peripheral shell, all the transition elements are metals. They demonstrate the qualities of metals, such as ductility and malleability they are excellent conductors of electricity and heat. Apart from Mercury, which is fluid and delicate like alkali metals, all the transition elements are hard and fragile.
Melting and boiling points
They show high melting and boiling points. This is due to the overlapping of (n-1)d orbitals and covalent bonding of the unpaired d orbital electrons. Zn, Cd, and Hg have totally filled (n-1)d orbitals. They cannot frame covalent bonds. Thus, they have a lower melting point than other d-block elements.
Ionic Radii
The transition elements are highly denser than the s block elements. Their densities gradually decrease from scandium to copper because of an irregular decrease in metallic radii and a relative increase in atomic mass. The pattern of the ionic radius is same as that of the atomic radii pattern. Hence, for ions of a given charge, the ionic radius gradually decreases with an increment in atomic number.
Ionization Potential
The ionization potential of transition elements lies between s and p block elements. They are less electropositive than the S-block elements. Henceforth, they do not frame ionic compounds but covalent compounds. They possess high ionization energy because of their small size.
The ionization potential of d-block elements increases from left to right. The ionization energies of the primary transition elements increase with the increase in the nuclear number. For example, Cr and Cu have high energies than their neighbours.
Electronic configuration
The external electronic configuration is consistent. There is a gradual filling of 3d orbitals across the series starting from scandium. However, this filling is not regular, since, at chromium and copper, the population of 3d orbitals increases by acquiring an electron from the 4s shell. At chromium, both the 3d and 4s orbitals are occupied, but neither of the orbitals is completely filled. This indicates that the energies of the 3d and 4s orbitals are relatively close for atoms in this row.
These three series of elements depend on the n-1 d orbital that is being filled. An orbital of lower energy is filled first. Therefore, 4s orbital with lesser energy is filled first to its full degree. After 4s, the 3d orbital with higher energy is filled. The precisely, half-filled and totally filled d-orbitals are
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