A transition element is one whose atom has a partially filled d or f sub-shell
or which can give rise to cations with a partially filled d or f sub-shell. This therefore, includes
the f-block elements (also known as the inner transition elements)
Transition elements are located in between the s-block and p- block elements in the periodic table of elements. They area also known as the d- block elements.
1) They are all metals with good thermal and electrical conductivity due to presence of delocalized electrons.
2) They have high tensile strength, density, melting point and boiling point – this is attributed to the ability of the d-orbital to delocalise with the metallic lattice in metallic bond formation.
3) Most display numerous oxidation states which vary in steps of 1 rather 2 as is usually the case with those main group elements which exhibit more than one oxidation state.
The d block elements show variable oxidation state because of their valence electrons in two different sets ,that is , (n-1) d and ns .
The energy difference between the orbitals is less , so both energy levels can be used for bond formation, thus transition elements have variable oxidation states .
Mn – have the highest number of unpaired electrons in the d subshell, it shows high oxidation state of +7 .
4) They have unparalleled propensity for forming coordination compounds with lewis bases due to their small size and high nuclear charge and availability of vacant d-orbitals .
5) Atleast one of their compound has an incomplete d-electrons subshell.
6) Transition elements and their compounds are often good industrial and biological catalysts. They are good heterogeneous and homogeneous catalysts.
This is because they are able to form numerous oxidation states and are able to form unstable intermediate compounds during a reaction providing an alternative route with a lower activation energy.
7) They form compounds which are paramagnetic.
Paramagnetism is where a substance contains one or more unpaired electrons. The unpaired electrons in (n-1) d orbital are responsible to magnetic properties. The magnetic property decrease with decrease in number of unpaired electrons>>> metals which contains paired electrons depicts diamagnetism.
8) Majority of transition elements form coloured compounds due to variable oxidation states . The colour of a complex complex compound depends on ;
i) The nature of the metal ion , specifically the oxidation state of the metal e.g Fe²+ – pale green , Fe ³+ – brown
ii) Arrangement of ligands around the metal ion e.g geometric isomer can display different colours.
iii) Nature of ligand surrounding the metal ion ( The stronger the ligand the greater the energy difference between the split high and low d groups .
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