Chemistry of Transition elements I

Note: My notes based on the order of learning outcomes presented in the syllabus.
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1) Definition of transtion elements
Transition elements are d block elements which form one or more stable ions with incompletely filled subshell of d electrons
Zn for example is not a transition element because the electronic configuration of Zn2+ is [Ar]3d10, i.e. its 3d subshells are completely filled

2) Electronic configuration of transition elements
The syllabus requires that students know the electronic configuration of transition metals from Sc to Zn. Remember that the 4s subshell is filled first before the 3d subshell. There are 5 orbitals in the 3d subshell. All 5 have to be singly filled before the electrons are paired
Special cases:
Cr: [Ar]3d5 4s1
Cu:[Ar]3d10 4s1

In both cases the 4s orbital is not completely filled due to the stability associated with a fully filled d shell and a half filled d shell

3) The atomic radii, ionic radii and first ionization energy of transition elements are similar.

4)Comparison between s block and transition element

Transition elements have higher melting points, higher densities and better conductivity than s block elements. This is due to the stronger metallic bonds present in transition elements. In transition elements, the d electrons and s electrons are available to take part in delocalisation. In contrast only the s electrons are able to delocalize in the s block element.

The atomic radius, ionic radius and first ionisation energy of d block elements are similar to s block element

5) Transition elements tend to have variable oxidation states

The difference in energy between the 3d and 4s electrons is much smaller than the difference in energy between the 3s and 3p electrons, hence the 3d and 4s electrons may be lost in chemical reactions.

6) Prediction of likely oxidation states given a particular electronic configuration

E.g. Fe is likely to have a +2 oxidation state due to the loss of the 2 outer most 4s electrons and a +3 oxidation state due to a loss of the 4s electrons and another 3d electrons giving rise to a stable half filled 3 d configuration

Note that some transition elements have oxidation state which are less obvious to predict. In the case of Ti, it is not easy to see why the main oxidation states of Ti are +3 and +4.

Continued in Chemistry of transition elements II
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