d – Block Elements

d – and f – Block Elements

Introduction :

→ The elements of the groups 3-12 in periodic table are known as d-block elements. In these elements valence electron enters to the penultimate d-subshell (.e.(n-1) d-subshell). These lie in between s-block and p block elements. The outer two orbitals of these elements are incompletely filled. These elements are known as transition elements.

Table 8.1: The position of transition elements in periodic table

→ In other words we can say that transition element is the one which has incompletely filled d-orbitals in its ground state or in any its oxidation states. The general electronic configuration of these elements is (n – 1)d^1-10 ns^{0, 1 or 2}

There are four transition series in the d-block. These are as follow :

→ 3d-series : In this series the last electron enters in 3d-subshell and its electronic configuration is 3d^1-10 4s^1-2. It includes the elements from atomic number 21 to 30. There are 10 elements in the series, which starts from Scandium (₂₁Sc) and ends at Zinc (₃₀Zn). It is also known a first transition series.

→ 4d-series : In this series the last electron enters in 4d-subshell and its electronic congfiguration is 4d^1-105s^1-2. It includes the elements having atomic number 39 to 48. There are 10 elements in this series, which starts from Yattrium (₃₉Y) and ends at Cadmium (₄₈Cd). It is also know as second transition series.

→ 5d-series : In this series the last electron enters in 5d^1-106s^1-2. It includes the elements having atomic number 57 and 72 to 80. Thus there are 10 elements in this series, which has Lanthanum (₅₇La), Hafnium (₇₂Hf) to Mercury (₈₀Hg). It is also known as third transition series.

→ 6d-series : In this series the last electron enters in 6d-subshell and its electronic congfiguration is 6d^1-10 7s^1-2. It includes the elements having atomic number 89 and 104 to 112.

→ Thus there are 10 elements in this series which has Actinium (₈₉Ac), Rutherfordium (₁₀₄Rf) to Ununbium (₁₁₂Uub). It is also known as fourth transition series. The elements with atomic number 104 to 112 are synthesised recently. These elements are knwon as trans actinoid sereis.

Summary and glossory

• Cerium is the most occuring lanthanides. It exists about 3 × 10^-4 % on earth crust. It is twentysixth most abundant of all the elements.
• Monazite sand is the most common mineral of lanthanides.
• The E° value of Ce⁴⁺/Ce is +1.74 V so it can oxidise water but the reaction is very slow hence Ce (IV) is a good analytical reagent.
• Lathanides show limited number of oxidation atates because the energy gap between of and 5d subshells is large.
• It is very interesting to note that lanthanide ions with xf electrons have a similar colour to those with (14- x)f electrons e.g., La³⁺ and Lu³⁺ are colourless. Sm³⁺ and Dy³⁺ are yellow and Eu³⁺ and Th³⁺ are pink.
• Actinides show a large number of oxidation states. This is because of very small energy gap between 58, 6d and 78 subshells. Hence all their electrons can take part in bond formation.
• Th is used in atomic reactor and treatment of cancer.
• U and Pu are used as fuel in nuclear reactor.
• Misch metal (n = 95%, Fe = 5%, S, C, Ca, Al = traces). It is used in making ug based alloy. It is pysophoric alloy (emits spark when struck) used in making bullets, shells, ligher flints etc.
• Actinides are silvery white metals. Their cations are coloured due to f-f transition.
• The element, whose atom in ground state or ion in one of its common oxidation state has incomplete d-subshell, is known as transition element.
• The general electronic configuration of transition elements is (n-1)d^1-10ns^1-2.
• Tungstun (w) has the highest melting point among the d-block elements.
• Technetium (TC) is a synthetic transition element.
• All transition elements are d-block elements but all d-block element are not transition element.
• For example group-12 elements i.e. Zn, Cd, Hg are not considered as transition elements yet they belong to d-block because they have completely filled (n-1)d orbitals and they do not show typical transition elements properties.
• Group-3 elements i.e. Sc, Y, La, Ac are also differ from other transition elements as they do not show variable oxidation state. They show only +3 oxidation states. So their compounds are colourless and dimagnetic.
• From the above given reasons group-3 and group-12 elements are called ‘non-typical transition elements’ while the rest are called ‘typical transition elements’.
• Ruthenium (Ru) and Osmium (Os) show highest oxidation state i.e. +8 in their compounds.
• Transition metal compounds show isomorphism due to similarity in the size of their metal ions.
  eg.FeSO₄ 7H₂O and ZnSO₄ . 7H₂O.
• Transition metal are generally coloured both in solid as well as in aqueous state. The colour of compounds is due to presence of unpaired electron and d-d transition. The colour of some common ions are as follow

• The paramagnetism of transition metal ions can be calculated with the help of spin-only formula – µ = √n(n + 2) B.M. (where n = no. of unpaired electrons)

Chemistry Notes