Transition Metal Article Index for
Transition 		Articles about
Transition Metal 		Website Links For
Transition 		 

Information About

Transition Metal
  CATEGORIES ABOUT TRANSITION METAL
   
periodic table
   
transition metals
   
SHOPPER'S DELIGHT
 
Shop For:  
Department
Price Minimum:
Price Maximum:
      




  • More strictly, IUPAC defines the transition metals as any element with an incomplete ''d'' subshell or that may form stable ions only with an incomplete ''d'' subshell ( IUPAC definition : "An element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell."). By this definition, Zinc , Cadmium , and Mercury are excluded from the transition metals, as they have a ''d''10 configuration. Only a few transient species of these elements that leave ions with a partly filled ''d'' subshell have been formed, and mercury(I) only occurs as Hg22+, which does not strictly form a lone ion with a partly filled subshell, and hence these three elements are inconsistent with the latter definition.Cotton, F. Albert; Wilkinson, G.; Murillo, C. A. (1999). ''Advanced Inorganic Chemistry'' (6th ed.). New York: Wiley. They do form ions with a 2+ oxidation state, but these retain the 4''d''10 configuration. Element 112 may also be excluded although its oxidation properties are unlikely to be observed due to its radioactive nature. This definition includes groups 3 to 11 on the periodic table.


The first definition is simple and has been traditionally used. However, many interesting properties of the transition elements as a group are the result of their partly filled subshells from ''d'' orbitals, a property which all members of the d-block except Zinc , Cadmium and Mercury share.


THE 40 TRANSITION METALS

The (loosely defined) transition metals are the forty chemical elements 21 to 30, 39 to 48, 71 to 80, and 103 to 112. The name ''transition'' comes from their position in the Periodic Table of elements. In each of the four periods in which they occur, these elements represent the successive addition of electrons to the ''d'' Atomic Orbital s of the atoms. In this way, the transition metals represent the ''transition'' between Group 2 Element s and Group 13 Element s.


ELECTRONIC CONFIGURATION

Elements with atomic numbers 1 through 20 have only electrons in ''s'' and ''p'' orbitals, with no filled ''d'' orbitals in their ground states.

In the fourth period, elements with atomic numbers 21 to 29 ( Scandium to Copper ) have a partially filled ''d'' subshell or ions with partly filled ''d'' subshell. The outer n''s'' orbitals in the ''d''-block elements are of lower energy than the (n-1)''d'' orbitals. As atoms occur in their lowest energy state, the transition metals tend to have their n''s'' orbitals filled with electrons. Hence, these elements all have two Electron s in their outer ''s'' orbital, with the exception of Copper ( and Chromium ([Ar 4''s''13''d''5). These exceptions occur because half- and fully-filled subshells impart unusual stability to the atoms. Similar exceptions are more prevalent in the fifth, sixth and seventh period.


PROPERTIES

Transition elements tend to have high Tensile Strength , Density and Melting and Boiling points. As with many properties of transition metals, this is due to ''d'' orbital electrons' ability to Delocalise within the metal lattice.
In metallic substances, the more electrons shared between nuclei, the stronger the metal.

There are several common characteristic properties of transition elements:


VARIABLE OXIDATION STATES

As opposed to group 1 and group 2 metals, ions of the transition elements may have multiple, stable oxidation states, since they can lose ''d'' electrons without a high energetic penalty. Manganese, for example has two 4''s'' electrons and five 3''d'' electrons, which can be removed. Loss of all of these electrons leads to a 7+ oxidation state. Osmium and Ruthenium compounds are commonly isolated in stable 8+ oxidation states, which is among the highest for isolable compounds.

Certain patterns in oxidation state emerge across the period of transition elements:
  • The number of oxidation states of each ion increases up to Mn, after which they decrease. Later transition metals have a stronger attraction between Proton s and Electron s (since there are more of each present), which then would require more energy to remove the electrons.

  • When the elements are in lower oxidation states, they can be found as simple ions. However elements in higher oxidation states are usually bonded covalently to electronegative compounds such as O or F, often as a Polyatomic Ion such as Chromate , Vanadate , and Permanganate ions.


Other properties with respect to the stability of oxidation states:
  • Ions in higher oxidation states tend to make good oxidising agents, whereas elements in low oxidation states become reducing agents.

  • The 2+ ions across the period start as strong Reducing Agent s, and become more stable.

  • The 3+ ions start stable and become more Oxidizing across the period.



CATALYTIC ACTIVITY

Transition metals form good Homogeneous or Heterogeneous catalysts, for example Iron is the catalyst for the Haber Process .
Nickel or platinum is used in the hydrogenation of alkenes.


COLORED COMPOUNDS

We observe color as varying frequencies of electromagnetic radiation in the visible region of the electromagnetic spectrum. Different colors result from the changed composition of Light after it has been Reflected , transmitted or Absorbed after hitting a substance.
Because of their structure, transition metals form many different colored ions and complexes.
Color even varies between the different ions of a single element - MnO4− (Mn in oxidation state 7+) is a purple compound, whereas Mn2+ is pale-pink.

Coordination by Ligand s can play a part in determining color in a transition compound, due to changes in energy of the ''d'' orbitals. Ligand s remove degeneracy of the orbitals and split them in to higher and lower energy groups. The energy gap between the lower and higher energy orbitals will determine the color of light that is absorbed, as
electromagnetic radiation is only absorbed if it has energy corresponding to that gap. When a ligated ion absorbs light, some of the electrons are promoted to a higher energy orbital. Since, different frequency light is absorbed, different colors are observed.

The color of a complex depends on:
  • the nature of the metal ion, specifically the number of electrons in the ''d'' orbitals

  • the arrangement of the ligands around the metal ion (for example Geometric Isomer s can display different colors)

  • the nature of the ligands surrounding the metal ion. The stronger the ligands then the greater the energy difference between the split high and low 3''d'' groups.


The complex formed by the d block element zinc (though not strictly a transition element) is colorless, because the 3d orbitals are full - no electrons are able to move up to the higher group.


SEE ALSO



REFERENCE