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The d-block elements, also known as transition metals, are the elements that have partially filled d-orbitals. 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.
Electronic Configuration of d-Block Elements
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The electronic configuration of the transition elements follows the rules and configuration like (n-1) d5 ns1 or (n-1) d10ns1. These are highly stable elements in both their half-filled states and filled states of the D orbitals. The configuration of common d-Block elements is given below:
Position of d-Block Elements in the Periodic Table
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The d-block elements are placed at the center of the periodic table, as shown in pink in the figure. Since they are transition elements (or metalloids), they are placed in between metals(s block) and non metals (p block). The fourth row of elements has not been fully filled yet.
Position of d-Block Elements in the Periodic Table
General Properties Of d-Block Elements
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- 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
Trends in Atomic and Ionic Radii
In case of d-block elements, there an interesting phenomena, known as lanthanoid contraction which affects the overall atomic radii of d-block elements. The result of lanthanoid contraction is that the 2nd and 3rd d-block series have similar radii (For instance Zr 160 pm, Hf 159 pm). They have similar physical and chemical properties, more than expected. The trend is given in the figure below:
Trends in Atomic and Ionic Radii
Things to Remember
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Elements with partially filled d-orbitals are known as transition metals.
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This group of elements are placed in the middle of the periodic table (between s-block and p-block elements).
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These elements have a tendency to exhibit multiple oxidation states, form complex compounds, are tough and have high density.
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They exhibit lanthanoid contraction.
Sample Questions
Ques: Why are transition metals also termed ‘noble metals’? (1 mark)
Answer: The reason behind this is that these have low enthalpies of hydration and high enthalpy of ionization. As a result, these metals are highly resistant to acids. However, they react to acidic mixtures like aqua regia (a mixture of hydrochloric acid and nitric acid). But silver doesn’t dissolve in aqua regia too.
Ques: What are the uses of transition metals? (2 marks)
Answer - Some of the uses of transition metals are listed below
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Transition metals are highly used in the construction industry. This is because these have high tensile strength and show a lot of versatility
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Iron can also be used as a catalyst because it undergoes the Haber process and can be industrially produced
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Another transition element or metal like titanium are also used in aircraft and the nuclear power plants
- One of the most important transition elements which are very widely used is copper. This is used in the electrical wiring of houses because it has high tensile strength, and it’s very malleable and ductile. This is also highly electrically conductive, increasing the chances of it being used in the electrical wiring.
Ques: Transition metals generally form colored compounds.(DELHI 2017)
Answer: Transition elements are very reactive, and they form colored compounds. Transition elements have unpaired electrons. These unpaired electrons undergo d-d transition by absorption of energy, and they have a visible region, and then they emit light and show complementary colors. This is the reason why transition elements form colored compounds.
Ques: Zinc is not regarded as a transition metal. (DELHI 2017)
Answer: The Reason why zinc is not considered as a transition element or a transition metal is that zinc in its common oxidation state is +2, which shows that it has filled d orbitals. Since transition metals general electronic configuration doesn’t match with that of zinc, so zinc is not considered or not regarded as the transition element
Ques: Copper-I ion can’t be described in an aqueous solution? (2 marks)
Answer - Copper in its aqueous solution is more stable as compared to normal copper. It can explain such behavior because although Cu2+ in an aqueous solution that is the second ionization enthalpy of copper is very high, the hydration enthalpy of copper is also very negative, compensating for the high second ionization enthalpy. This results in the formation of unstable compound copper compounds in aqueous solution, and therefore this enables copper to undergo disproportionation reaction, which is explained below
2Cu+ = Cu2+ + Cu
Ques: Why do transition elements behave as a good catalyst? (CBSE 2012)
Answer: Transition elements have many features like high melting and boiling point, they are hard, they form colored compounds, and they are good catalysts. The reason behind there being a good catalyst is explained here. Transition elements have unpaired electrons in their incomplete d orbitals. Due to these unpaired electrons, they show high levels of oxidation States and therefore are regarded as good catalysts.
Ques: What do you understand by the term lanthanoid contraction? What are its consequences, if any? (3 marks)
Answer: The term lanthanide contraction is the overall decrease in the atomic and ionic radii when the atomic number increases. In the periodic table, when we go from La3+ to Lu3+, the size of the iron decreases. This decrease in the size of the iron in the lanthanide series is known as lanthanide contraction. Such behavior is imported because of the presence of the shielding effect of the electrons. Such behavior arises when a 14f electron is shielded by a different electron present in the same subshell.
There are the following characteristic features and consequences which are explained as a result of lanthanide contraction:-
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The similarity in properties: Because of the lanthanide contractions, the size of the elements Hf and Hg are almost similar concerning the previous row elements like Zr and Cd. Due to this similarity in size, it becomes difficult to separate the elements of these two rows since their atomic radii change very little. Thus, the chemical properties of the lanthanides are very similar, and the separation between the different lanthanide elements becomes difficult.
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The difference in basicity: Since the lanthanide contraction takes place, the covalent character increases. Because of the increase in the covalent characters, the basic characters of hydroxides also decrease, so La(OH)3 is the most basic while Lu(OH)3 is the least basic.
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