Question:

$Ti ^{3+}$ transition metal ion is purple in colour while $Ti ^{4+}$ metal ion is colourless due to

Updated On: Jun 14, 2022
  • vacant d-orbitals
  • unpaired electrons in d orbitals
  • completely filled d-orbitals
  • None of these
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The Correct Option is A

Solution and Explanation

Transitional metal ions having completely filled or empty d-orbitals,
ie, $(n-1) d^{10}$
or $(n-1) d^{0}$
configuration are colourless while transitional metal ions having $(n-1) d^{1-9}$
configuration are coloured due to $d - d$ transition.
$T i(22):[A r] 3 d^{2} A s^{2}$
$T i^{3+}:[A r] 3 d^{1} 4 s^{o}:$ purple
$T i^{4+}:[A r] 3 d^{0} 4 s^{o}:$ colourless
Hence, $T i^{4+}$ metal ion is colourless due to vacant d-orbitals.
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Concepts Used:

d block elements

The elements, in the columns of the periodic table in which d subshells are being occupied are known as d block elements. 

These are the elements that have the capability of forming stable cations with incompletely filled d orbitals. Elements like mercury and Zinc are not considered transition metals because they have electronic configurations: (n-1)d10 ns2. These elements have filled d-orbitals in their ground state and, therefore, even in some of their oxidation states. 

General Properties Of d-Block Elements

  • Multiple oxidation states- The oxidation states of d block elements show very few energy gaps; therefore, they exhibit many oxidation states. Also, the energy difference between s and d orbital is very less. Therefore both the electrons are involved in ionic and covalent bond formation, which ultimately leads to multiple oxidation states.
  • Formation of complex compounds- Ligands show a binding behaviour and can form so many stable complexes with the help of transition metals. This property is mainly due to:
    • Availability of vacant d orbitals.
    • Comparatively small sizes of metals.
  • Hardness- Transition elements are tough and have high densities because of the presence of unpaired electrons.
  • Melting and boiling points- Melting and boiling points of transition are very high. This is because of the presence of unpaired electrons and partially filled d orbitals. Because of these two things, they form strong bonds and therefore have high melting and boiling points.
  • Atomic radii- The atomic and ionic radius of the transition elements decreases as we move from Group 3 to group 6. However, it remains the same between group 7 and group 10, and from group 11 to group 12 increases.
  • Ionization enthalpy- The ionization enthalpies of the transition elements are generally on the greater side as compared to the S block elements