Write the important properties of transition metal
Answers
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...
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Densities and Metallic Radii
The transition elements are much denser than the s-block elements and show a gradual increase in density from scandium to copper. This trend in density can be explained by the small and irregular decrease in metallic radii coupled with the relative increase in atomic mass.
Variations of the melting point (blue curve) and boiling points (red) in the first row transition metals.
Ionization Energies
In moving across the series of metals from scandium to zinc a small change in the values of the first and second ionization energies is observed. This is due to the build-up of electrons in the immediately underlying d-sub-shells that efficiently shields the 4s electrons from the nucleus and minimizing the increase in effective nuclear charge Zeff from element to element. The increases in third and fourth ionization energy values are more rapid. However, the trends in these values show the usual discontinuity half way along the series. The reason is that the five d electrons are all unpaired, in singly occupied orbitals. When the sixth and subsequent electrons enter, the electrons have to share the already occupied orbitals resulting in inter-electron repulsions, which would require less energy to remove an electron. Hence, the third ionization energy curve for the last five elements is identical in shape to the curve for the first five elements, but displaced upwards by 580 kJ mol-1.
Oxidation States
Transition metals can form compounds with a wide range of oxidation states. Some of the observed oxidation states of the elements of the first transition series are shown in Figure 23.1.5 . As we move from left to right across the first transition series, we see that the number of common oxidation states increases at first to a maximum towards the middle of the table, then decreases. The values in the table are typical values; there are other known values, and it is possible to synthesize new additions. For example, in 2014, researchers were successful in synthesizing a new oxidation state of iridium (9+).
A table is shown with 10 columns and 8 rows. The first row is the header, which shows element symbols with atomic numbers as superscripts to the upper left of the element symbols. The following element symbols and numbers are shown in this manner; S c 21, T i 22, V 23, C r 24, M n 25, F e 26, C o 27, N i 28, C u 29, and Z n 30. The second row shows the value 1 plus under C u. The third row shows the value 2 plus under V, C r, M n, F e, C o, N i, C u, and Z n. The fourth row shows the value 3 plus under S c, T i, V, C r, M n, F e, C o, N i, and C u. The fifth row shows the value 4 plus under T I, V, C r, and M n. The sixth row shows the value 5 plus only under V. The seventh row shows the value 6 plus under C r, M n, and F e. The eighth row shows the value 7 plus under Mn.
Figure 23.1.5 :Transition metals of the first transition series can form compounds with varying oxidation states.
For the elements scandium through manganese (the first half of the first transition series), the highest oxidation state corresponds to the loss of all of the electrons in both the s and d orbitals of their valence shells. The titanium(IV) ion, for example, is formed when the titanium atom loses its two 3d and two 4s electrons. These highest oxidation states are the most stable forms of scandium, titanium, and vanadium. However, it is not possible to continue to remove all of the valence electrons from metals as we continue through the series. Iron is known to form oxidation states from 2+ to 6+, with iron(II) and iron(III) being the most common. Most of the elements of the first transition series form ions with a charge of 2+ or 3+ that are stable in water, although those of the early members of the series can be readily oxidized by air.
The elements of the second and third transition series generally are more stable in higher oxidation states than are the elements of the first series. In general, the atomic radius increases down a group, which leads to the ions of the second and third series being larger than are those in the first series. Removing electrons from orbitals that are located farther from the nucleus is easier than removing electrons close to the nucleus. For example, molybdenum and tungsten, members of group 6, are limited mostly to an oxidation state of 6+ in aqueous solution. Chromium, the lightest member of the group, forms stable Cr3+ ions in water and, in the absence of air, less stable Cr2+ ions. The sulfide with the highest oxidation state for chromium is Cr2S3, which contains the Cr3+ ion. Molybdenum and tungsten form sulfides in which the metals exhibit oxidation states of 4+ and 6+.