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D-block Elements


Three series of elements are formed by filling the 3d, 4d and 5d shells of electrons. Together these comprise the d-block elements. They are often called transition elements because their position in the periodic table is between the s-block and p-block elements. Their properties are transitional between highly reactive metallic elements of the s-block which typically form ionic compounds and the elements of the p-block which are largely covalent.

Transition elements are those which either as neutral atoms or in any of their common oxidation states, have partly filled d-orbitals. According to this definition the elements Zn, Cd and Hg are excluded from the list of transition elements. However for the sake of completion of discussion on the d-block elements the elements Zn, Cd and Hg may be considered.

D Block on Periodic Table

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The d-block is found in the center of the periodic table. The transition elements are known as d-block elements. In the periodic table the elements belonging to groups 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 are together known as d-block elements.
The d-block elements are elements in which the differentiating electron enters an orbital in the (n-1)d sub shell. Most of the d-block elements have partly filled d orbitals. In the periodic table the d-block elements fill the central block constituting Groups 3 to 12. They are also called transition metals because their remarkably similar physical properties are characteristic of metals.

D Block on Periodic Table

Three series of d-block elements

The d-block elements form three horizontal series of 10 elements each in the periods 4, 5 and 6 wedged between groups 2 and 13 in the periodic table.
  • First transition series - involves the filling of 3d sub shell. It is therefore also called the 3d series. It consists of ten elements from 21Sc to 30Zn. These elements belong to the period 4 of the periodic table.
  • Second transition series - involves the filling of 4d sub shell. It is therefore also called the 4d series. It consists of ten elements from 39Y to 48Cd. These elements form part of the period 5 of the periodic table.
  • Third transition series - This series results from the filling of 5d sub shell. It is therefore also called the 5d series. It consists of ten elements from 57La to 80Hg which form part of the period 6 of the periodic table.

D Orbital Shape

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For the d-orbitals l=2 and m can take values -2, -1, 0, +1 and +2. The orbitals are named as dxy, dyz, dxz, dx2-y2 and dz2. These are shown in the following diagram. The dxy, dyz, dxz and dx2-y2 orbitals have four lobes each.

In the absence of the magnetic and electrical fields they are all equivalent in energy and are said to be five fold degenerate. The shapes and features of these d-orbitals can be described as follows.
D Orbital Shape

The set of three orbitals dxy, dyz, dxz have their lobes lying symmetrically between the coordinate axes. For example, the lobes of dxy orbital are lying between x and y axes. The dx2-y2 and dz2 orbitals have their lobes along the axes. For example the lobes of dx2-y2 orbital are along the x and y axes and those of dz2 are along the x-axis. Besides the dz2 orbital has an annular ring in the xy plane.

Each of the dxy, dyz and dxz have double dump bell shape. In the case of dxy the lobes of xy component will be positive when both x and y are positive and xy will be negative when both x and y are negative. If one breaks the orbital shapes in the form of four quadrants the sign will be either positive or negative in the opposite quadrants. Similarly the other two dyz and dxz have the same description for the shape and signs.

D Orbital

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The d-orbitals are in general more complicated in shape than the p-orbitals. With the exception of dz2 orbital all the d-orbitals have four lobes alternating in sign. While p-orbitals have one nodal plane the d-orbitals have two nodal planes. The energy of an orbital increases as the number of nodal planes increases.

The d-orbitals can thus be divided into two different types. The dx2-y2 and dz2 belong to one type and these orbitals lie along the axial directions while the other type namely dxy, dyz and dxz point along 45o angle to the axial directions. Because of this difference in orientation the energies of the two types of orbitals are differently affected by the applied electric fields.

D Orbital Electrons

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Atoms are made up of even smaller particles called electrons, neutrons and protons. The neutrons and protons cluster together in the dense center or nucleus of the atom. The electrons revolve around the nucleus in orbits called electron shells which correspond to the energy of the electrons within them.

Only a certain number of electrons can occupy each electron shell. For example, up to two electrons can occupy the electron shell nearest the nucleus up to eight electrons can occupy the next electron shell, and up to 18 electrons can occupy the third electron shell. Electrons also travel in paths called orbitals within these electron shells. There are four different orbitals called s, p, d and f having different shapes which determine how many electrons they can hold. The d orbital can hold up to ten electrons.
The oxidation state of an atom in a compound is defined as the charge which it would carry in the most probable ionic formulation of the compound. This is decided on the basis of the electronegativities of the elements in the compound. The common oxidation states of the elements are related to their electronic configurations.
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Catalysis is homogeneous when the catalyst is soluble in the reaction medium and heterogeneous when the catalyst is existing in a phase distinctly different from the phase of the reaction medium. In most instances of heterogeneous catalysis the catalyst is a solid that is brought into contact with gas or liquid reactants to bring about a transformation.
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