What are D Block Elements?
D block elements are the elements which can be found from the third group to the twelfth group of the modern periodic table. The valence electrons of these elements fall under the d orbital.
These elements typically display metallic qualities such as malleability and ductility, high values of electrical conductivity and thermal conductivity, and good tensile strength.
The first three rows of the d block elements which correspond to the 3d, 4d, and 5d orbitals respectively are given below. These elements are also referred to as transition elements or transition metals.
General Electronic Configuration of d Block Elements
The electronic configuration of the d-Block elements can generally be written as (n-1)d1-10ns1-2. These elements can find stability in half-filled orbitals and completely filled d orbitals. An example of this would be the electronic configuration of chromium, which has half filled d and s orbitals in its configuration – 3d54s1.
The electronic configuration of copper is another such example. Copper displays an electronic configuration of 3d104s1 and not 3d94s2. This can be attributed to the relative stability of the completely filled d orbital.
Zinc, Mercury, Cadmium, and Copernicium exhibit completely filled orbitals in their ground states and in their general oxidation states as well. For this reason, these metals are not considered as transition elements whereas the other d block elements are.
Properties of d Block Elements
The physical and chemical properties of the d block elements are discussed below. It can be noted that Zinc, Cadmium, and Mercury generally do not exhibit properties that are similar to the other elements belonging to the d block and have been mentioned as exceptions wherever applicable.
Physical Properties of d Block Elements
As mentioned earlier, these elements typically exhibit metallic qualities such as metallic luster and are good conductors of heat and electricity. These elements have at least one metallic structure at room temperature (excluding Zinc, Cadmium, Mercury, and Manganese).
The d-Block elements are hard, non-volatile and have high melting and boiling points. The melting points of the d block elements increase as we progress from the 3d to the 5d orbitals. They have relatively high atomization enthalpies.
Atomic Size and Ionic Size
Due to the increase in effective nuclear charge along the row, the ionic radii of these elements decreases from left to right in a given row. In a similar fashion, the atomic radii of the d block elements are also found to shrink as we progress through a given series.
Since the 4f orbitals are filled before the 5d orbitals, there arises a regular decrease in the radii of the atoms. This decrease in atomic radii is referred to as lanthanoid contraction.
Enthalpy of Ionization
The enthalpy of ionization increases along the series from left to right. This is due to the increase in effective nuclear charge which occurs as the inner d orbitals are filled.
The ionization enthalpies of the first three series of the d block elements suggest that the successive enthalpies do not increase as steeply as they do in the case on non-transition metals.
Oxidation States of the d Block Elements
These elements generally exhibit a large variety of oxidation states. In a given series, the element with the highest number of oxidation states can be found towards the middle. In the first series of the transition metals, manganese is found in the 5th position and exhibits the greatest number of oxidation states (all states from +2 to +7).
The incomplete filling of the d orbital in the case of these elements causes them to vary in their oxidation states by 1. This is highlighted in the list of oxidation states of the first row of d block elements provided below:
It can be noted that the number of oxidation states exhibited by these elements is relatively low at the beginning and at the end of a given series due to there being only a few d electrons and too many d electrons respectively.
Chemical Reactivity and Magnetic Properties
These elements differ in their chemical reactivity. For example, many of these transition metals can be dissolved by mineral acids. However, a few more inert metals belonging to this category such as copper remain unaffected.
When compared to the other series of the transition metals, the elements belonging to the first series (excluding copper) are considered more reactive.
Many ions of transition metals exhibit paramagnetic properties, i.e. CHEMICAL PROPERTIES OF D-BLOCK ELEMENTS AND THEIR COMPOUNDS ASSIGNMENTthey are attracted by applied magnetic fields.
Formation of Complexes and Interstitial Compounds
Complex compounds are compounds wherein a number of neutral molecules or anions are bound to a metal. Metals which are a part of the d block elements form many complex compounds owing to their small ionic size, high charge, and relative availability of d orbitals for the formation of bonds.
Sometimes, smaller atoms like carbon, nitrogen, or hydrogen get trapped in the crystal lattices of metals with atoms which are comparatively larger in size. These resulting compounds are called interstitial compounds and they have the following properties:
- Their melting points are very high.
- They are extremely hard.
- They have similar conductivity properties when compared to other metals
- They are unreactive and tend to be chemically inert.
Examples for the interstitial compounds that are formed with transition metals are TiC and Fe3H.
Important Compounds of d Block Elements
The transition metals form some compounds of vital industrial importance. Some such compounds include:
1. K2Cr2O7 (Potassium Dichromate)
This compound is considered very important in the leather industry. It is also used as an oxidant in most azo compound preparing processes.
The structure of the dichromate ion is made up of two tetrahedra that share a single corner with a Chromium-Oxygen-Chromium bond angle of 1260. Potassium dichromate is a strong oxidizing agent.
Potassium dichromate is also used as a primary standard in the process of volumetric analysis.
2. KMnO4 (Potassium Permanganate)
The physical appearance of KMnO4 has an intense purple color. It exhibits diamagnetic properties and also weak paramagnetic properties which are reliant on the temperature. The permanganate ion exhibits diamagnetism due to the absence of unpaired electrons in it.
Potassium permanganate is also used as an oxidant in the preparation of various products in organic chemistry. It also finds use in the bleaching of cotton, silk, and wool. It can also be used for the decolorization of oils owing to its strong oxidizing ability.