General Properties of Transition Elements (d-block)

Elements with partially filled d orbitals are known as transition elements (sometimes known as transition metals). Transition elements are defined by IUPAC as elements with a partially full d subshell or elements capable of forming stable cations with an incompletely filled d orbital. 

In general, any element that corresponds to the contemporary periodic table’s d-block (groups 3-12) is considered a transition element. Even the lanthanides and actinides, which are part of the f-block elements, can be classified as transition metals. However, because f-block elements contain partially full f-orbitals, they are frequently referred to as inner transition elements or inner transition metals.

Placement of Transition Elements

The transition metals are still present between the s and p block elements. They are primarily classified into three groups.

1. First transition series (Sc to Cu)
2. Second transition series (Y to Ag)
3. Third transition series (La and the elements from Hf to Au)

Lanthanides and actinides are f-block elements found in the sixth and seventh series. Lanthanides are the fourteen elements ranging from Cerium to Lutetium. Actinides, on the other hand, are the fourteen elements ranging from nuclear number 90 (Thorium) to 103 (Lawrencium). The elements of actinides are radioactive, and those over Z=92 are usually created by humans in accelerators or nuclear reactors. Copper, iron, and silver are all significant transition elements. Furthermore, titanium and iron are the most prevalent.

General Properties of Transition Elements

The configuration of electrons corresponds to (n-1)d⁵ ns¹ or (n-1)d¹⁰ ns¹. This is because of the stability provided by the half-filled or completely filled electron orbitals. Because their electrical configurations differ from those of other transition metals, zinc, cadmium, and mercury are not considered transition elements. However, the characteristics of the remaining d-block elements are somewhat similar, and this resemblance can be seen down each row of the periodic table. 

If we proceed from left to right through the periodic table, the properties of the second and third-row elements gradually alter. These elements’ outer shells have low shielding effects, which increase the effective nuclear charge as more protons are added to the nucleus. These transition element attributes are listed below.

1. These elements combine to generate colored compounds and ions. This color is explained by the electron d-d transition.
2. The energy gap between these elements’ potential oxidation states is relatively small. As a result, the oxidation states of transition elements are diverse.
3. Because of the unpaired electrons in the d orbital, these elements create a large number of paramagnetic compounds.
4. These elements can be bound by a wide range of ligands. As a result, transition elements generate a wide range of stable complexes.
5. These elements have a high charge-to-radius ratio.
6. Transition metals are hard and have relatively high densities when compared to other elements.
7. Because delocalized d electrons participate in metallic bonding, the boiling and melting temperatures of these elements are high.
8. Because of the metallic bonding of the delocalized d electrons, the transition elements are also strong conductors of electricity.

Several transition metals possess catalytic capabilities that are extremely useful in the commercial manufacture of certain compounds. Iron, for example, is employed as a catalyst in the Haber process for producing ammonia. Vanadium pentoxide, on the other hand, is utilized as a catalyst in the commercial synthesis of sulfuric acid.

• Oxidation State: Because transition elements exist in various oxidation states, their atoms might lose a varied number of electrons. Because the energies of the ns and (n – 1)d-subshells are nearly comparable, this is owing to the participation/contribution of inner (n – 1) d-electrons in addition to outer ns-electrons. When both of its 4s- electrons are used for bonding, the oxidation state of sc is +2. When it employs its two s- electrons and one d- electron, it can also indicate the oxidation state of +3. The other atom has oxidation states of ns and (n – 1) d- electrons as well. Zn has an oxidation state of +2. The oxidation states of chromium range from +2, +3, +4, +5, +6. Chromium has the highest oxidation state of +6.
• Atomic Ionic Radii: Because of the inadequate shielding provided by the tiny amount of d-electrons, the atomic and ionic radii of the transition elements decrease from group 3 to group 6. Those placed between groups 7 and 10 have atomic radii that are roughly similar, but those placed between groups 11 and 12 have bigger radii. This is because electron-electron repulsions balance out the nuclear charge. As you move down the group, you’ll see an increase in the atomic and ionic radii of the elements. The presence of a greater number of subshells can explain the rise in radius.
• Ionization Enthalpy: The amount of energy required to remove a valence electron from an element is referred to as its ionization enthalpy. The larger the effective nuclear charge acting on electrons, the greater the element’s ionization potential. As a result, the ionization enthalpies of transition elements are often higher than those of s-block elements.
• Metallic Radii and Densities: The transition metals are denser than the s-block metals, and the density increases from scandium to copper. This density factor varies because of the uneven decrease of metallic radii and the increase of atomic mass. As a result, the ionic radius reduces while the atomic number increases.
• Boiling and Melting Points: Because of the overlapping of (n – 1)d orbital and d orbital unpaired electrons in covalent bonding, these elements have high boiling and melting temperatures. Metals with entirely full (n-1)d orbitals include Hg, Cd, and Zn. Because they cannot form covalent bonds, their boiling points are lower than those of the other d-block elements.
• Metallic Nature: Because the transition elements have fewer electrons in their outermost shells, they are all metals. As a result, they have all of the properties of a metal, such as a malleability and ductility. They are also excellent heat and electricity conductors. Except for mercury, which is liquid and more akin to alkali metals, all of these elements are hard and fragile.
• Chemical Reactivity: Transition elements exhibit a variety of chemical properties. Some metals have high reductivity based on their reduction potentials, while others have low reductivity. For example, all lanthanides produce 3+ aqueous cations. Metals with high reductivity, such as gold and platinum, on the other hand, can resist oxidation and are excellent for producing jewelry and circuits.

Sample Problems

Question 1: What are the metallic qualities of the transition metals?

Solution:

Transition metals have typical metallic qualities such malleability, ductility, high tensile strength, and metallic lustre. They tend to crystallize and are generally good conductors of heat and electricity. Trends in the metallic characteristics of the transition elements, on the other hand, can be seen. Because they contain a large number of unpaired electrons, elements such as chromium and molybdenum are among the hardest transition metals.

Question 2: Why are some transition metals referred to as noble metals?

Solution: 

Noble metals are elements in the lower right corner of the contemporary periodic table’s d-block (such as gold, silver, and platinum). Because of their low hydration enthalpies and high ionisation enthalpies, these metals are very unreactive.

Question 3: What are the uses of transition metals?

Solution: 

The transition element nickel is mostly used in the manufacturing of stainless steel. Copper, a transition metal, is often used in electrical wire due to its high tensile strength, malleability, ductility, and electrical conductivity.

Question 4: Why are all the transition elements metals?

Solution:

Because all transition elements have only two electrons in their outermost shells, they are all metals. They are also malleable, hard, and ductile due to strong metallic connections.

Question 5: What are inner transition elements?

Solution:

Lanthanides and actinides are two groupings of elements in the periodic table. These groups have a total of 30 elements known as inner transition elements. They are usually placed behind the core area of the periodic table.